,transcriber's ,notes3 ,underscores 80 before and after a word or phrase indicate italics in the original text4 ,small capitals have been converted to ,,solid capitals4 ,illustrations have been moved so they do not break up paragraphs4 ,illustration3 ,,ski-,,optometer ,,master ,,model #bae ,embodying in a ,single ,instrument1 in ,convenient ,form1 ,cylindrical and ,spherical ,lenses1 in ,combination with ,appliances for ,testing and ,correcting ,muscular ,imbalance4 ,refraction and ,muscular ,imbalance ,as ,simplified ,through the ,use of the ,ski-optometer ,by ,,daniel ,,woolf ,,woolf ,,instrument ,,corporation ,,new ,,york3 #eaf ,,fifth ,,avenue ,copyright #aiba ,by ,,woolf ,,instrument ,,corporation ,published by ,,theodore ,s4 ,,holbrook ,,new ,,york ,,contents ,,chapter ,i ,page ,,ski-,,optometer ,,construction #a ,convex ,spherical ,lenses #b ,operates and ,indicates ,automatically #f ,concave ,spherical ,lenses #g ,,chapter ,,ii ,,cylindrical ,,lenses #aj ,obtaining ,correct ,focus #aa ,why ,concave ,cylinders ,are ,used ,exclusively #ad ,transposition of ,lenses #ad ,,chapter ,,iii ,,how ,,the ,,ski-,,optometer ,,assists ,,in ,,refraction #ag ,the ,use of the ,ski-optometer in ,skioscopy #ag ,a ,simplified ,skioscopic ,method #bj ,employing ,spheres and ,cylinders in ,skioscopy #bb ,use of the ,ski-optometer in ,subjective ,testing #bc ,a ,simplified ,subjective ,method #bd ,procedure for ,using ,minus ,cylinders ,exclusively #bf ,constant ,attention ,not ,required #bi ,,chapter ,,iv ,,important ,,points ,,in ,,connection ,,with ,,the ,,use ,,of ,,the ,,ski-,,optometer #cj ,elimination of ,trial-,frame ,discomfort #cj ,rigidity of ,construction #ca ,how to ,place the ,ski-optometer in ,position #cb ,cleaning the ,lenses #cc ,accuracy ,assured in ,every ,test #cd ,built to ,last a ,lifetime #ce ,,chapter ,v ,,condensed ,,procedure ,,for ,,making ,,sphere ,,and ,,cylinder ,,test ,,with ,,the ,,ski-,,optometer #cg ,subjective ,distance ,test #cg ,subjective ,reading ,test #dj ,,chapter ,,vi ,,muscular ,,imbalance #da ,the ,action of ,prisms #db ,the ,phorometer #dc ,the ,maddox ,rod #dd ,procedure for ,making the ,muscle ,test #de ,binocular and ,monocular ,test #dg ,,chapter ,,vii ,,the ,,binocular ,,muscle ,,test #dh ,made with the ,maddox ,rod and ,phorometer #dh ,esophoria and ,exophoria #ej ,making ,muscle ,test ,before and ,after ,optical ,correction #eb ,when to ,consider ,correction of ,muscular ,imbalance #ec ,four ,methods for ,correction of ,muscular ,imbalance #ed ,the ,rotary ,prism #ed ,use of the ,rotary ,prism in ,binocular ,muscle ,tests #ef ,,chapter ,,viii ,,the ,,monocular ,,duction ,,muscle ,,test #eh ,made with ,both ,rotary ,prisms #eh ,locating the ,faulty ,muscle #eh ,adduction #ei ,abduction #fa ,superduction #fb ,subduction #fc ,procedure for ,monocular ,muscle ,testing #fd ,diagnosing a ,specific ,muscle ,case #fe ,,chapter ,,ix ,,first ,,method ,,of ,,treatment--,,optical ,,correction #gj ,esophoria #gj ,treatment for ,correcting ,esophoria in ,children #gb ,how ,optical ,correction ,tends to ,decrease #f ,esophoria in a ,child #gd ,,chapter ,x ,,second ,,method ,,of ,,treatment--,,muscular ,,exercise #ge ,made with ,two ,rotary ,prisms and ,red ,maddox ,rod #ge ,exophoria #ge ,an ,assumed ,case #gh ,effect of ,muscular ,exercise #hj ,home ,treatment for ,muscular ,exercise--,square ,prism ,set ,used in ,conjunction with the ,ski-optometer #hb ,,chapter ,,xi ,,third ,,method ,,of ,,treatment--,,prism ,,lenses #hd ,when and ,how ,employed #hd ,prism ,reduction ,method #he ,,chapter ,,xii ,a ,,condensation ,,of ,,previous ,,chapters ,,on ,,the ,,procedure ,,for ,,muscle ,,testing ,,with ,,the ,,ski-,,optometer #hg ,four ,methods of ,treating an ,imbalance ,case when the ,preceding ,one ,fails #ij ,prisms #ib ,cyclophoria #ib ,,chapter ,,xiii ,,cyclophoria #ic ,made with ,maddox ,rods and ,rotary ,prisms #ic ,,chapter ,,xiv ,,cycloduction ,,test #ii ,made with the ,combined ,use of the ,two ,maddox ,rods #ii ,treatment for ,cyclophoria #ajb ,,chapter ,,xv ,,movements ,,of ,,the ,,eyeballs ,,and ,,their ,,anomalies #aje ,monocular ,fixation #aje ,binocular ,fixation #ajf ,orthophoria #ajg ,heterophoria #ajg ,squint #ajh ,varieties of ,heterophoria and ,squint #aji ,,chapter ,,xvi ,,law ,,of ,,projection #aad ,suppression of ,image #aae ,monocular ,diplopia #aae ,table of ,diplopia #aaf ,movement of ,each ,eye ,singly #aag ,subsidiary ,actions #aah ,field of ,action of ,muscles #abj ,direction of the ,gaze #abj ,primary ,position--,field of ,fixation #aba ,binocular ,movements #aba ,parallel ,movements #abb ,lateral ,rotators #abc ,eye ,associates #abd ,movements of ,convergence #abe ,movements of ,divergence #abe ,vertical ,divergence #abf ,orthophoria #abf ,heterophoria #abf ,subdivisions #abf ,,chapter ,,xvii ,,symptoms ,,of ,,heterophoria #abh ,treatment #acj ,destrophoria and ,laevophoria #acb ,the demands of the day for maximum efficiency in the refracting world are largely accountable for the inception1 continuous improvement and ultimate development of the master model ,ski-optometer4 ,the present volume1 dealing with the instrument's distinctive operative features1 has been prepared not only for ,ski-optometer users1 but also for those interested in the simplification of refraction and muscular imbalance4 ,the author is indebted for invaluable counsel1 to ,louis ,j4 ,ameno1 ,m4,d41 ,new ,york4 ,e4 ,le,roy ,ryer1 ,o4,d41 ,new ,york4 ,jos4 ,d4 ,heitger1 ,m4,d41 ,louisville1 ,ky4 ,w4 ,b4 ,needles1 ,n4,d41 ,kansas ,city1 ,mo4 ,,introductory ,while in a measure the conventional trial-case still serves its purpose1 so much of the refractionist's time is consumed through the mechanical process of individually transferring the trial-case spheres and cylinder lenses1 that far too little thought is given to muscular imbalance1 notwithstanding its importance in all refraction cases4 ,dr4 ,samuel ,theibold1 of ,johns ,hopkins ,university1 in a recent address before the ,american ,medical ,association1 stated that the average refractionist was inclined to devote an excess of time to general refraction1 completely overlooking the important test and correction of muscular imbalance4 ,if the latter is to be at all considered1 general refraction must be simplified--without impairing its accuracy--a result that is greatly facilitated through the use of the ,ski-optometer4 ,one must admit that tediously selecting the required trial-case lens--whether sphere1 cylinder or prism--watching the stamped number on the handle--continual wiping and inserting each individual lens in a trial-frame is a time-consuming practise4 ,this is readily overcome1 however1 through the employment of the ,ski-optometer4 ,in a word1 the ,ski-optometer is practically an automatic trial-case1 bearing the same relation to the refracting room as the accepted labor and time-saving devices of the day bear to the commercial world4 ,the present volume has accordingly been published1 not alone in the interest of those possessing a ,ski-optometer1 but also for those interested in attaining the highest point of efficiency in the work of refraction and muscular imbalance4 ,illustration3 ,ski-optometer ,lens ,battery 7almost actual size7 showing how sphere and cylinder lenses are procured4 ,after obtaining ,,final results1 your prescription is automatically registered1 ,,all ,,ready for you to transcribe4 ,fig4 #a--,the three time-saving moves necessary in the operation of the ,ski-optometer4 ,,chapter ,i ,,ski-,,optometer ,,construction ,a far better understanding of the instrument will be secured if the refractionist possessing a ,ski-optometer will place it before him1 working out each operation and experiment step by step in its proper routine4 ,the three moves as outlined in ,fig4 #a should first be thoughtfully studied and the method of obtaining the spheres and cylinders carefully observed4 ,illustration3 ,fig4 #b--,to ,obtain ,plano4 #a--,set spherical indicator at 8#jjj0 as illustrated above4 #b--,set cylinder indicator to 8#j04 #c--,set pointer of supplementary disk at 8open04 ,the instrument should then be set at zero or 8plano10 a position indicated by the appearance of the three 8#j #j #j0 at the spherical register1 in conjunction with one 8#j0 or zero1 for the cylinder at its register1 marked 8,,cc ,cyl40 ,after this move1 the supplementary disk's pointer should be set at 8open0 7,fig4 #b74 ,illustration3 ,fig4 #c--,to obtain sphericals1 turn this ,single ,reel as shown by dotted finger4 ,this assures an automatic and simultaneous registration at sphere indicator of focus of lens appearing at sight opening4 ,,convex ,,spherical ,,lenses ,a careful study will show that the ,ski-optometer's spherical lenses are obtained by merely turning the smaller reel 7,fig4 #c74 ,the first outward turn of this reel1 toward the temporal side of the instrument1 draws into position in regular order the spherical lenses 4#be1 4#ej1 4#ge1 and #a4;,d41 as shown in ,fig4 #c;a4 ,illustration3 #c-;,a--,outer spherical reel containing ,cx4 sphericals from 4#jbe to #a4jj;,d and a blank4 ,illustration3 #c-;,b--,inner spherical disk containing ,cx4 sphericals1 automatically turns within #c-;,a4 ,illustration3 #c-;,c--,supplementary spherical disk4 ,by means of a concealed tooth gear1 an inner disk is automatically picked up1 placing its first lens #a4be;,d in position 7,fig4 #c;b74 ,this #a4be;,d spherical lens remains stationary while the outer disk again revolves1 adding to it the original 4#be1 4#ej1 4#ge and #a4;,d41 the latter totalling #b4be;,d4 ,at this point1 the instrument again automatically picks up its inner disk1 thereby placing its second lens1 #b4ej;,d1 in position4 ,illustration3 ,fig4 #d--,with the reappearance of 8#jj0 at sphere indicator1 a rapid increase or decrease of #a4be is accurately and speedily attained4 ,instead of using intermediate strengths in making an examination1 it is frequently desirable to make such extended changes as #a4be;,d to #b4ej;,d4 ,with the ,ski-optometer1 the refractionist will note that two white zeros appeared at the spherical register in connection with #a4be1 and again with #b4ej4 ,a rapid outward turn of the spherical reel toward the temporal side to the point of the reappearance of the two zeros will show #c4ge;,d2 or1 if increased power is still desired1 a rapid turn will draw #e4;,d4 into position 7,fig4 #d74 ,turning the reel inward toward the nasal side will likewise decrease its convex power4 ,in brief1 each one of these lenses1 showing their foci in conjunction with the two white zeros1 are signals indicating the rapid increase or decrease of one and one-quarter diopter4 ,after continuing to #f;,d41 the next turn automatically shows zero 7or 8plano071 the original starting point1 which is again indicated by the three white zeros4 ,through the turn of the single reel--an exclusive ,ski-optometer feature--all convex spherical lenses have now been attained in quarters up to #f4;,d1 practically covering ninety percent of all refraction cases4 ,illustration3 ,fig4 #e--,with supplementary disk pointer set at #f ,sph41 this places an additional #f4;,d spherical lens at sight opening1 extending instrument's total convex spherical power to #ab4;,d4 ,should still greater power be desired1 the small pointer at the outer edge of the instrument should be set at #f sphere 7,fig4 #e74 ,this controls a supplementary disk 7,fig4 #c;c7 which places an additional #f;,d4 lens before the original range of lenses previously referred to1 thus increasing the maximum power to #ab;,d4 ,if still greater strength is required1 any additional trial-case lens may be added1 a cell being provided for that purpose on the forward plate of the instrument4 ,,operates ,,and ,,indicates ,,automatically ,as previously explained1 in using the ,ski-optometer1 it is only necessary to remember that each outward turn of the single reel toward the temporal side of the patient increases the plus power1 while the reverse turn toward the patient's nose decreases it4 ,in fact1 no attention need ever be given the register until the required sum-total is secured1 it only being necessary to turn the single reel in order to be assured of the unvarying and accurate operation of the instrument4 ,for convenience1 the contour or upper edge of the plate covering the spherical reel has been made to fit the index finger 7,fig4 #c74 ,hence the operator should note that it requires but one complete turn from extreme side to side1 rather than a number of short turns1 in order to bring each individual lens into position1 thus obtaining the full advantage of the automatic spring-stop4 ,this likewise permits the refractionist to operate the ,ski-optometer even though the room is in total darkness4 ,,concave ,,spherical ,,lenses ,another simple and exclusive ,ski-optometer advantage worthy of note is the method employed in obtaining concave1 spherical lenses4 ,instead of employing a battery of concave lenses similar to the convex battery previously described1 the instrument's operation is greatly simplified through the use of a neutralizing process4 ,in short1 the ,ski-optometer only contains two concave lenses to obtain its entire series--namely1 a -#f4;,d and a -#ab4;,d sphere 7,fig4 #c;c7--first setting the pointer of the supplementary disk at -#f4 sphere1 then setting the indicator of the spherical battery at #f4 ,thus zero 7or plano7 is obtained1 the plus neutralizing the minus4 ,by merely turning the plus or convex spherical reel inward1 or toward the patient's nose1 the convex power is then decreased1 naturally increasing the concave value or total minus lens power4 ,for example1 if the spherical indicator shows #e4;,d1 when the -#f;,d4 lens is placed behind it1 the lens value at the sight opening will be -#a;,d 7,fig4 #f74 ,if required1 the refractionist may continue on this plan until only the -#f;,d4 lens remains4 ,illustration3 ,fig4 #f--,with this indicator of supplementary disk1 set at -#f4;,d4 ,sph4 and spherical indicator at #e4;,d--lens value at sight opening is -#a4;,d4 ,sph4 ,this simple arrangement makes it possible to operate the ,ski-optometer with but ,single ,reel for both plus and minus sphericals4 ,should concave power stronger than -#f;,d4 be desired1 by placing the pointer of the supplementary disk at -#ab;,d4 ,sph4 and proceeding to neutralize as before1 all the concave powers up to -#ab;,d4 in quarters are similarly obtained4 ,for the convenience of the operator1 all minus or concave spherical powers are indicated in red2 while plus1 or convex powers1 are indicated in white4 ,the instrument is also provided with an opaque or blank disk which is brought into position before the sight opening by setting the pointer of the supplementary disk at 8shut0 7,fig4 #c;c47 ,summing up1 all plus and minus spherical powers have been attained from zero to #ab;,d4 in quarters1 practically through the turn of the single reel--a simplicity of operation largely responsible for ,ski-optometer supremacy4 ,,chapter ,,ii ,,cylindrical ,,lenses ,it is commonly admitted that setting each trial-case cylindrical lens at a common axis is the most tedious part of refraction4 ,the automatic cylinder1 one of the ,ski-optometer's latest and distinctly exclusive features1 not only overcomes this annoyance but also avoids the need of individually transferring each cylindrical lens according to the varying strengths4 ,illustration3 ,fig4 #g--,once you set the axis indicator as shown by dotted fingers1 each cylindrical lens in the instrument automatically positions itself exactly at that axis1 as indicated by the arrow4 ,by merely setting the ,ski-optometer's axis indicator 7,fig4 #g71 each cylindrical lens in the instrument automatically positions itself1 so that it will appear at the opening at the exact axis indicated4 ,this is readily accomplished by placing the thumb on the small knob1 or handle of the axis indicator1 drawing it outward so as to release it from spring tension4 ,the indicator may then be set at any desired axis2 and1 on releasing the handle1 every cylinder in the instrument becomes locked1 making it impossible for any lens to appear at an axis other than the one specified by the indicator4 ,this insures the absolute accuracy of the axis of every cylinder as it appears before the patient's eye4 ,subsequent shifting of the axis even to a single degree is impossible1 although it is a common occurrence where trial-case lenses are employed4 ,,obtaining ,,correct ,,focus ,after setting the axis indicator1 the only remaining move is to obtain the correct cylindrical strength or focus4 ,this is readily accomplished by merely turning the ,ski-optometer's larger or extreme outer single reel1 which contains concave cylindrical lenses from 4#be;,d to #b;,d in quarters 7,fig4 #h;a74 ,it should again be borne in mind that a downward turn increases concave cylinder power1 while an upward turn decreases it4 ,the operation of the cylinder reel is greatly facilitated by carefully noting position of thumb and index finger 7,fig4 #h74 ,thus accuracy of result1 simplicity of operation and the saving of much valuable time is invariably assured4 ,illustration3 ,fig4 #h;,a--,inner cog-wheel construction1 showing arrangement of ,ski-optometer cylinders4 ,this simple construction assures accuracy and avoidance of the slightest shifting of axes4 ,as each cylinder appears before the patient's eye1 it simultaneously registers its focus at the indicator marked 8,,cc ,,cyl0 shown in ,fig4 #h4 ,examinations of greater accuracy could not possibly be made than those obtained through the ,ski-optometer1 hence no refractionist should hesitate to employ it throughout an entire examination--wherever trial-case lenses are used4 ,the range of the ,ski-optometer's cylinder lens battery includes up to #b;,d4 in quarters4 ,an axis scale and a cell is located at the back of the instrument for insertion of an additional trial-case cylinder lens1 when stronger cylindrical power is required4 ,for example1 if an additional -#b;,d4 cylinder is added1 it will increase the range up to #d;,d4 cylinder2 or if twelfths are desired1 a #j4ab;,d4 cylinder lens may be inserted4 ,in this connection1 it is interesting to note that considerable experimenting with twelfths in the ,ski-optometer proved them to be needless1 inasmuch as the instrument's cylindrical lenses set directly next to the patient's eyes overcome all possible loss of refraction1 as explained in a later paragraph4 ,illustration3 ,fig4 #h--,turn this ,single ,reel as shown by dotted finger to obtain cylindrical lenses1 which simultaneously register their focus as they appear4 ,each lens also automatically positions itself at axis designated4 ,,why ,,concave ,,cylinders ,,are ,,used ,,exclusively ,the ,ski-optometer contains only concave cylinders1 as it is universally admitted that convex cylinders are not essential for testing purposes4 ,in fact1 concave cylinders should alone be used in making an examination1 even where a complete trial-case is employed4 ,to repeat one of the first rules of refraction3 8,as much plus or as little minus spherical power as patients will accept1 combined with weakest minus cylinder1 simplifies the work of refraction and insures accuracy without time-waste40 ,after an examination with the ,ski-optometer is completed1 the total result of plus sphere and minus cylinder may be transposed if desired1 though in most instances it is preferable to prescribe the exact findings indicated by the instrument4 ,this will also avoid every possibility of error1 eliminating responsibility where one is not familiar with transposition--since1 after all1 it is the duty of the optician to thoroughly understand that part of the work4 ,,transposition ,,of ,,lenses ,it is commonly understood that transposition of lenses is merely change of form1 but not of value4 ,for example1 a lens #a4jj sph4 -4#ej cyl4 axis #ahj may be transposed to its equivalent1 which is 4#ej sph4 4#ej cyl4 axis #ij4 ,the accepted formula in this special instance is as follows3 ,algebraically add the two quantities for the new sphere1 retain the power of the original cylinder1 but change its sign and reverse its axis #ij degrees4 ,applying this rule1 a lens 4#ge sph4 -4#be cyl4 axis #ahj1 is equivalent to 4#ej sph4 4#be cyl4 axis #ij4 ,similarly1 a lens #a4jj sph4 -#a4jj cyl4 axis #ahj is equivalent to #a4jj cyl4 axis #ij4 ,one of the difficulties in transposing is in reversing the axis4 ,in such cases1 it is well to memorize the following simple rule3 ,to reverse the axis of any cylindrical lens containing three numerals--add the first two together and carry the last4 ,for example1 from #aje to #ahj degrees1 etc43 #aje ,add--one and 8#j0 equals #a ,then carry the #e #ae #abj ,add--one and two equals #c ,then carry the #j #cj #acj ,add--three and one equals #d ,then carry the #j #dj #aej ,add--five and one equals #f ,then carry the #j #fj #afe ,add--six and one equals #g ,then carry the #e #ge #ahj ,add--eight and one equals #i ,then carry the #j #ij ,to transpose where there are but two numerals1 #ij should be added4 ,in using the ,ski-optometer1 it is absolutely unnecessary to transpose the final result of an examination2 merely write the prescription as instrument indicates4 ,the idea that plus sphere combined with minus cylinder1 or the reverse1 is an incorrect method of writing a prescription1 has long since been disproved4 ,,chapter ,,iii ,,how ,,the ,,ski-,,optometer ,,assists ,,in ,,refraction ,the construction of the ,ski-optometer has now been fully explained1 and the reader realizes that since the instrument contains all the lenses necessary in making an examination1 greater operative facility is afforded through its use than where the trial-case lenses are employed4 ,the ,ski-optometer is 8an automatic trial-case0 in the broadest sense of the term1 wholly superseding the conventional trial-case4 ,it should therefore be employed throughout an entire examination1 wherever trial-case lenses were formerly used4 ,to fully realize its labor saving value in obtaining accurate examination results1 it is only necessary to recall the tedious method of individually handling and transferring each lens from the trial-case to the trial-frame1 watching the stamped number on each lens handle1 wiping each lens and in the case of cylindrical lenses setting each one at a designated axis--all being needless steps where the ,ski-optometer is employed4 ,,the ,,use ,,of ,,the ,,ski-,,optometer ,,in ,,skioscopy ,in skioscopy1 the ,ski-optometer offers the refractionist assistance of the most valuable character4 ,for example1 assuming that extreme motion in the opposite direction with plane or concave mirror is obtained with a #a4be;,d4 spherical lens before the patient's eye2 by quickly turning the ,ski-optometer's single reel until the two white zeros again appear1 #b4ej;,d is secured1 as explained in the previous chapter4 ,if this continues to give too much 8against motion10 the lens power should be quickly increased to #c4ge or #e4jj;,d if necessary 7,fig4 #d74 ,should the latter reveal a shadow in the reversed direction1 the refractionist is assured that it is the weakest lens that will cause its neutralization4 ,practically but few lenses have been used to obtain the final result proving the instrument's importance and time-saving value in skioscopy1 and demonstrating the simplicity with which tedious transference of trial-case lenses is avoided4 ,furthermore1 it should be noted that where the ,ski-optometer is used in skioscopy1 it is not necessary to remove the retinoscope from the eye or to constantly locate a new reflex with each lens change4 ,this permits a direct comparison of the final lens and eliminates the usual difficulty in mastering skioscopy4 ,the chief cause of this difficulty is due to the fact that the transferring of the trial-case lenses makes it practically impossible for the student to determine whether the previous lens caused more 8with0 or 8against0 motion4 ,illustration3 ,fig4 #i--,the ,woolf ophthalmic bracket4 ,a convenient and portable accessory in skioscopy and muscle testing2 can be used with or without ,greek cross4 ,where the indirect method is employed in skioscopy1 best results are secured through the use of the ,woolf ophthalmic bracket and concentrated filament lamp1 together with an iris diaphragm chimney4 ,the latter permits the reduction or increase of the amount of light entering the eye1 as it is agreed that a large pupil requires less light1 a small pupil requiring more light4 ,the bracket referred to permits the operator to swing the light into any desired position 7,fig4 #i71 while the iris diaphragm chimney serves as a shutter4 ,this apparatus may also be employed for muscle testing1 as described in a subsequent paragraph4 ,a ,,simplified ,,skioscopic ,,method ,in using the ,ski-optometer1 instead of working forty inches away from the patient in skioscopy and deducting #a4;,d41 the refractionist will find it more convenient to work at a twenty inch distance1 deducting #b4;,d4 ,this working distance may be accurately measured and maintained by using the reading rod accompanying the instrument4 ,instead of deducting #b4;,d4 from the total findings1 however1 it is preferable to insert a #b4;,d4 trial-case lens in the rear cell of the instrument directly next to the patient's eye4 ,after determining the weakest lens required to neutralize the shadow in both meridians1 the additional #b4;,d4 lens should be removed and the total result of the examination read from the instrument's register4 ,to illustrate a case in skioscopy where spherical lenses are employed to correct both meridians1 assume that the vertical shadow requires a #a4be;,d lens to cause its reversal1 while the horizontal requires #b4jj;,d4 ,employment of the customary diagram1 illustrated in ,fig4 #aj1 would show the patient required #a4be sph4 4#ge cyl4 axis #ij1 which when transposed is equivalent to #b4jj sph4 -4#ge cyl4 axis #ahj4 ,illustration3 ,fig4 #aj--,where spherical lenses are employed in skioscopy1 above indicates patient requires #a4be ,sph4 4#ge ,cyl4 ,axis #ij or #b ,sph4 -4#ge ,cyl4 ,axis #ahj ,it should be noted that the total spherical power is #b4jj;,d1 as the ,ski-optometer's register shows1 while the difference between the two meridians is #ge1 which is the required strength of the cylinder4 ,by then turning the cylinder reel to 4#ge1 and setting the axis indicator at #ahj 7because by using minus cylinders1 the axis must be reversed7 the patient should read the test-type with ease if the skioscopic findings are correct4 ,thus with the ,ski-optometer1 it is not even necessary to learn transposition1 since the instrument automatically accomplishes the work1 avoiding all possibility of error4 ,,employing ,,spheres ,,and ,,cylinders ,,in ,,skioscopy ,another commonly used objective method may be employed with even greater facility through the combined use of both the ,ski-optometer's spherical and cylindrical lenses4 ,as previously suggested1 insert the #b4jj spherical trial-case lens in the rear of the instrument1 working at a twenty inch distance1 then proceed to correct the strongest meridian first4 ,it was assumed that it required a #b4jj spherical to neutralize the strongest1 or horizontal meridian1 as shown in ,fig4 #aj4 ,the refractionist should then set the axis indicator therewith1 which is the axis of the cylinder1 or #ahj4 ,it is then merely a matter of increasing the ,ski-optometer's cylindrical lens power until the reversal of the shadow in the weakest meridian is determined4 ,assuming this proves to be -4#ge cylinder1 axis #ahj1 the patient's complete prescription #b4jj sph4 -4#ge cyl4 axis #ahj1 would be registered in the ,ski-optometer without any further lens change other than the removal of the #b4jj working distance lens4 ,however1 regardless of the method employed1 the ,ski-optometer greatly simplifies skioscopy4 ,in fact1 the instrument was originally intended to simplify retinoscopy or skioscopy1 as the subject should be termed1 the name 8,ski-optometer0 having been derived from the latter4 ,,use ,,of ,,the ,,ski-,,optometer ,,in ,,subjective ,,testing ,in subjective refraction1 especially where the 8better or worse0 query must be decided by the patient1 it is commonly understood that the refractionist is compelled to first increase and then decrease a quarter of a diopter before the final lens is decided4 ,with the ,ski-optometer1 the usual three final changes are made in far less time than it takes to make even one lens change from trial-case to trial-frame4 ,for example3 ,assuming1 with a #a4be;,d spherical lens before the patient's right eye1 he remarks that he 8sees better0 with a #a4;,d4 while 4#ge;,d is not as satisfactory4 ,the refractionist can then quickly return to #a4;,d41 simply turning the ,ski-optometer's single reel outward to increase1 or backward to decrease1 the lens strength4 ,so rapidly have these lens changes been made1 that the patient quickly sees the difference of even a quarter diopter1 and quickly replies1 8better0 or 8worse40 ,this is made possible because the eye does not 8accommodate0 as quickly as the lens change made with the ,ski-optometer4 ,it should also be noted that the eye receives an image on its retina within one-sixteenth of a second2 otherwise1 the patient is forced to accommodate1 making it difficult to see the difference of even a quarter diopter4 ,on the other hand1 in transferring trial-case lenses1 with its slow1 tedious procedure1 the patient1 being unable to detect the slight difference of only a quarter diopter1 unhesitatingly replies1 8no difference10 merely because they are compelled to accommodate4 ,a ,,simplified ,,subjective ,,method ,the following simplified method of procedure is suggested for subjective testing with the ,ski-optometer1 although as previously explained1 the refractionist may employ his customary method1 overcoming the annoyance of transferring trial-case lenses and the setting of each cylinder individually4 ,the ,ski-optometer has been constructed and based upon the golden rule of refraction3 8,as much plus or as little minus spherical1 combined with as little minus cylinder power as the patient accepts40 ,by applying this rule as in the above method and starting with #e4;,d4 spherical1 watching the two zeros 7,fig4 #d7 and rapidly reducing #a4be;,d each time1 we will assume that #a4be;,d gives #bj_/cj vision2 as a final result #a4;,d4 will possibly give #bj_/be vision4 ,the patient's attention should next be directed to the most visible line of type1 preferably concentrating on the letter 8,e0 or the clock dial chart--either of which will assist in determining any possible astigmatism4 ,since the ,ski-optometer contains concave cylinders exclusively1 the next move should be the setting of its axis indicator at #ahj1 commonly understood as 8with the rule40 ,one should then proceed to determine the cylinder lens strength by turning the reel containing the cylindrical lenses 7,fig4 #h74 ,should the patient's vision fail to improve after the -4#ej;,d4 cylinder axis #ahj has been employed1 the refractionist1 in seeking an improvement1 should then slowly move the axis indicator through its entire arc4 ,with the cylinder added1 regardless of axis1 poor vision might indicate the absence of astigmatism4 ,if astigmatism exists1 vision will usually show signs of improvement at some point1 indicating the approximate axis4 ,once the latter is ascertained1 the refractionist may readily turn the ,ski-optometer's cylinder reel and obtain the correct cylinder lens strength1 after which the axis indicator should be moved in either direction in order to obtain the best possible vision for the patient4 ,the refractionist should always aim to obtain normal 7or #bj_/bj7 vision with the weakest concave cylinder1 combined with the strongest plus sphere1 or weakest minus sphere4 ,,procedure ,,for ,,using ,,minus ,,cylinders ,,exclusively ,for the benefit of those who have never used minus cylinders exclusively in making their examinations1 we will assume that the patient requires ,o4,u4 #a4;,d sph4 -#a;,d cyl4 axis #ahj for final correction2 the latter1 in its transposed form1 being equivalent to #a4;,d4 cylinder axis #ij4 ,unquestionably the best method is the one that requires the least number of lens changes to secure the final result4 ,to obtain this1 the following order of lens change should be made3 ,first1 #a4;,d4 sphere is finally determined and allowed to remain in place4 ,concave cylinders are then employed in quarters until the final results of #a4;,d4 spherical1 combined with -#a4;,d4 cylinder axis #ahj is secured4 ,this necessitates the change of but four cylindrical lenses as shown in routine 8,a0 as follows3 ,,routine 8,a0 ,,routine 8,b0 7,made with minus cylinder7 7,made with plus cylinder7 ,sph4 #a4;,d4 ,cyl4 ,axis ,sph4 #a4;,d4 ,cyl4 ,axis ,step #a #a4;,d4 -4#be ax4 #ahj equal to 4#ge 4#be ax4 #ij ,step #b #a4;,d4 -4#ej ax4 #ahj equal to 4#ej 4#ej ax4 #ij ,step #c #a4;,d4 -4#ge ax4 #ahj equal to 4#be 4#ge ax4 #ij ,step #d #a4;,d4 -#a ax4 #ahj equal to #j #a ax4 #ij ,in brief the method of using minus cylinders exclusively in an examination1 as explained in routine 8,a01 necessitates the change of the cylinder lenses only after the strongest plus sphere is secured4 ,on the other hand1 notwithstanding innumerable other methods where plus cylinders are used1 routine 8,b0 shows that the best spherical lens strength the patient will accept1 is also first determined4 ,then both spheres and cylinders are changed in their regular order by gradually building up in routine1 by increasing plus cylinder and next decreasing sphere1 a quarter diopter each time1 until the final result is secured4 ,while it is conceded that both routine 8,a0 and 8,b0 are of themselves simplified methods1 by comparing routine 8,a0 where minus cylinders are used with routine 8,b0 where plus cylinders are used in their corresponding steps1 the refractionist will note by comparison that one is the exact equivalent and transposition of the other4 ,where plus cylinders are employed1 eight lens changes are made before final results are secured2 while but four lens changes are necessary where minus cylinders are used4 ,the refractionist should also note by comparison that the use of minus cylinders reduces focus of the plus sphere1 but only in the meridian of the axis4 ,it has not made the patient myopic4 ,furthermore1 a plus cylinder will bring the focal rays forward1 while minus cylinders throw them backward toward the retina4 ,this is but another reason for the exclusive use of minus cylinders in refraction4 ,the method of using minus cylinders exclusively in an examination1 necessitates the change of the cylinder lenses only4 ,on the other hand1 the method of using plus cylinders makes it necessary to change spheres and cylinders in routine4 ,in brief1 since using the minus cylinder is merely a matter of mathematical optics1 their use even in a trial-case examination is strongly urged4 ,the maximum value of the ,ski-optometer is fully realized only when the advantages of using minus cylinders exclusively in every examination is clearly understood4 ,,constant ,,attention ,,not ,,required ,with the ,ski-optometer1 when the examination is completed1 the sum-total of final results--whether spherical1 cylinder1 axis1 or all combined--are automatically indicated or registered ready to write the prescription4 ,until then1 the foci of the various lenses that may be employed are of no importance4 ,in short1 in using the ,ski-optometer1 it is not necessary to constantly watch the registrations during examinations4 ,the automatic operation of the instrument is an exclusive feature1 so that the refractionist should unhesitatingly employ it4 ,hence1 by eliminating the perpetual watch on the lenses in use1 the refractionist is enabled to give his undivided attention to the patient rather than to the trial lenses4 ,where a special dark-room is used for skioscopic work1 an additional wall bracket or floor stand will necessitate only the removal of the instrument itself4 ,this enables the refractionist to use the ,ski-optometer for subjective or objective work1 without disturbing the patient's correction4 ,,chapter ,,iv ,,important ,,points ,,in ,,connection ,,with ,,the ,,use ,,of ,,the ,,ski-,,optometer ,the ,ski-optometer is equipped with an adjustable head-rest1 permitting its lenses to be brought as close as possible to the eye without touching the patient's lashes1 a matter of importance in every examination4 ,illustration3 ,fig4 #aa--,the nasal lines of the ,ski-optometer fit the contour of face with mask-like perfection1 patient remaining in comfortable position4 ,,elimination ,,of ,,trial-,,frame ,,discomfort ,where the ,ski-optometer is correctly fitted to the face1 the patient invariably remains in a comfortable position 7,fig4 #aa74 ,the instrument is shaped to fit the face like a mask1 so that even with a pupillary distance of but #ej m_/m 7that of a child7 there still remains1 without pinching1 ample room for the widest nose of an adult4 ,before making an examination1 the correct pupillary distance should always be obtained by drawing an imaginary vertical line downward through the center of each eye from the #ij point on the ,ski-optometer axis scale4 ,the pupillary distance will then register in millimeters on the scale of measurements for each eye separately4 ,if the ,ski-optometer is correctly adjusted1 the patient is securely held in position1 the cumbersome trial-frame being entirely eliminated4 ,,rigidity ,,of ,,construction ,illustration on following page 7,fig4 #aa;a7 shows the reinforced double bearing arms which hold the ,ski-optometer lens batteries at two points4 ,this eliminates possibility of the instrument getting out of alignment1 and prevents wabbling or loose working parts4 ,the broad horizontal slides shown in the cut1 move in and out independently so that the pupillary distance is obtained for each eye separately by turning the pinioned handle on either side of the instrument4 ,the scale denotes in millimeters the ,p4,d4 from the median line of the nose outward1 the total of both scales being the patient's pupillary distance4 ,fig4 #aa;a also serves to show the staunch construction of the base of the ,ski-optometer4 ,illustration3 ,fig4 #aa;a--,showing staunch construction of ,ski-optometer base4 ,,how ,,to ,,place ,,the ,,ski-,,optometer ,,in ,,position ,the patient should be placed in a comfortable position with 8chin up10 as though looking at a distant object4 ,the instrument should then be raised or lowered by the adjustable ratchet wheel of the bracket4 ,the wall bracket gives best results when suspended from the wall1 back of the patient1 as shown on page #ace4 ,this bracket should be placed about ten inches above the head of the average patient4 ,when the ,ski-optometer is placed in position for use1 its lower edge will barely touch the patient's cheeks4 ,it is sometimes advisable to request the patient to lightly press toward the face the horizontal bar supporting the instrument4 ,particularly good results are secured where a chair with a head-rest is employed in conjunction with the ,ski-optometer4 7,see illustration of ,model ,refraction ,room1 ,page #aab74 ,,cleaning ,,the ,,lenses ,the time-waste of perpetually cleaning lenses is overcome where the ,ski-optometer is employed4 ,for the convenience of the operator and protection of ,ski-optometer lenses1 the latter are concealed in a dust-proof cell1 overcoming all dust and finger-print annoyances4 ,when not in use1 the instrument should be covered with the standardized hood forming part of the equipment4 ,the instrument should not be taken apart under any circumstances4 ,to clean its lenses1 not a single screw need be removed1 as the lenses of each disk may be cleaned individually through the opening of the other disks4 ,these openings are conveniently indicated by the white zeros 7,fig4 #b74 ,the ,ski-optometer contains but eleven spherical and eight cylindrical lenses on each side1 so that the actual work of cleaning should not require over ten minutes at the most1 cleaning the lenses every other week proving quite sufficient4 ,,accuracy ,,assured ,,in ,,every ,,test ,loss of refraction is completely eliminated through the use of the ,ski-optometer4 ,the most casual examination of the trial-frame or any other instrument shows that the construction necessitates the placing of the spherical lens next to the eye with the cylinder lens outermost--a serious fault wholly overcome in the ,ski-optometer4 ,not only do the cylindrical lenses of the ,ski-optometer set directly next to the patient's eye1 thus overcoming any possible loss of refraction1 but the strong spherical lenses of the supplementary disk are set directly next to the cylinder4 ,there is apparently but a hair's distance between these lenses2 the two disks containing the spherical lenses of the ,ski-optometer likewise setting close together4 ,in a word1 the ,ski-optometer's cylinder lenses set directly next to the patient's eye1 followed by the stronger sphericals1 so that the weakest spherical or 4#be 7the lens of least importance7 sets farthest away4 ,this is #c m_/m closer than any trial-frame manufactured1 however1 and at least #aj m_/m closer than any other instrument--another reason for implicitly relying on the ,ski-optometer for uniformly accurate results4 ,,built ,,to ,,last ,a ,,lifetime ,illustration3 ,fig4 #ab--7;,a4 and ,b47--,this unique1 patented split-spring device of screwless construction1 securely holds all movable parts4 ,in case of repair1 they may be removed with the blade of a knife4 ,the ,ski-optometer is built on the plan of _/1 insuring absolute rigidity and accuracy and a lifetime of endurance4 ,particular and detailed attention has been given to the novel means of eliminating screws which either bind1 create friction or continually work loose1 causing false indications of findings on scales of measurements2 hence correct and accurate indications are insured in the ,ski-optometer by means of a split-spring washer construction similar to that of an automobile tire's detachable rim 7,fig4 #ab74 ,this patented spring washer construction securely holds the phorometer lenses1 the rotary prism and the revolving cylinder lens cells4 ,whenever necessary1 or in case of repair1 these parts may be readily removed with the blade of a knife4 ,,chapter ,v ,,condensed ,,procedure ,,for ,,making ,,sphere ,,and ,,cylinder ,,test ,,with ,,the ,,ski-,,optometer ,notwithstanding various methods employed1 for both subjective and objective refraction1 the following synopsis of the previous chapters will unquestionably prove most valuable to the busy refractionist1 enabling him to make error-proof examinations in practically every case without resorting to the transference of trial-case sphere or cylinder lenses4 ,a careful reading of chapters one and two should be made however1 so that one may gain an understanding as to how spheres and cylinders are obtained with the ,ski-optometer4 ,,subjective ,,distance ,,test #ast--,place ,ski-optometer in position1 employing spirit level1 thus maintaining instrument's horizontal balance4 #bnd--,adjust the pupillary distance for each eye individually1 by drawing an imaginary vertical line downward through the center of each eye from the #ij point on the ,ski-optometer's axis scale4 ,the opaque disk should be placed before the patient's left eye by setting the supplementary disk handle at 8shut40 #crd--,the ,ski-optometer lens battery before the patient's right eye should be set at 8open0 7figure #b71 whereupon the first turn of spherical lens battery toward the nasal side places a #f4;,d sphere in position4 ,this should blur vision of average patient4 #dth--,it is now only necessary to remember that an outward turn toward temporal side of the instrument increases plus sphere power1 while a nasal turn decreases it4 ,therefore continue to reduce convex spherical lens power until the large letter 8,e0 on the distant test card is clear4 ,then request patient to read as far down as possible1--a rapid turn of a quarter diopter being readily accomplished with the ,ski-optometer 7,fig4 #d74 #eth--,in the event of working down to 8zero0 with spheres1 the supplementary disk handle or indicator should next be set at -#f4;,d sphere1 while the spherical reel should be turned toward the nasal side--thus building up on minus spheres 7,fig4 #f74 ,in short1 the strongest plus sphere or weakest minus sphere should always be determined before employing cylinders4 #fth--,with the best spherical lens that the patient will accept left in place1 direct attention to the letter ,e or ,f in the lowest line of type the patient can see on the distant test letter chart4 ,then set axis indicator at #ahj 7,fig4 #g74 #gth--,next increase concave cylinder power until vision is improved4 ,if vision is not improved after increasing cylinder strength to -4#ej axis #ahj1 merely reverse the axis to #ij4 ,if vision is improved1 cylinder lens strength should be increased4 ,if not1 it should be decreased 7,fig4 #h74 #hth--,slowly move axis indicator through entire arc of axis1 thus locating best possible axis 7,fig4 #g74 #ith--,after sphere and cylinder test of right eye has been made1 place supplementary disk handle at 8shut40 ,then repeat procedure in testing left eye4 #ajth--,after completing examination for each eye separately1 then1 with both of the patient's eyes open1 direct attention to lowest line of type he can see1 concentrating on the ,e or ,f1 simultaneously increasing or decreasing spherical power before both eyes4 ,the refractionist merely recalls that by turning the ,ski-optometer's single reel toward the temporal side1 convex spherical power is increased1 by turning toward the nasal side for either eye1 spherical power is decreased4 ,cylinder lens strength may be changed in a like manner before both eyes simultaneously4 #aath--,after making the distance test1 then only is it necessary to copy the result of the examination as recorded by the ,ski-optometer4 ,,subjective ,,reading ,,test ,tilt ,ski-optometer forward in making reading test4 ,the wide groove in the horizontal bar supporting the instrument1 permits it to be slightly tilted4 #abth--,place ,ski-optometer reading rod in position with card at about #ad inches4 ,close off one eye4 ,direct patient's attention to the name 8,benjamin0 printed at top of card4 #acth--,leave cylinder lens in place4 ,proceed as in distance test with #f4;,d sphere1 fogging down until the first word 8laugh0 on the reading card1 in line #ge,m1 is perfectly clear1 this being slightly smaller than the average newspaper type4 #adth--,after completion of examination for each eye separately1 then with both eyes direct patient's attention to word 8laugh40 ,move reading card in or out a few inches either side of #ad inch mark4 ,this will determine any possibility of an over-correction4 ,then record prescription just as ,ski-optometer indicates4 ,for a detailed description of above1 as well as for objective testing with the ,ski-optometer1 read chapter three4 ,,chapter ,,vi ,,muscular ,,imbalance ,the purpose of the present chapter is to acquaint the refractionist with the operation of the ,ski-optometer as 8a scientific instrument for muscle testing0--the subject being treated as briefly and comprehensively as is practicable4 ,as the reader progresses in the subject of muscular anomalies1 he may carry his work to as high a plane as desired1 increasing his professional usefulness to an enviable degree4 ,through the use of the ,ski-optometer1 muscle testing may be accurately accomplished in less time than a description of the operation requires4 ,furthermore1 tedious examinations may be wholly overcome through the discontinuance of the consecutive transference of the various degrees of prisms from the trial-case4 ,in fact1 the latter method has long been quite obsolete1 owing to the possibility of inaccuracy4 ,the muscle action of the eye is usually quicker than the result sought through the use of trial-case prisms2 hence muscle testing with the ,ski-optometer is accomplished with far greater rapidity and accuracy1 thus making the instrument an invaluable appliance in every examination4 ,,the ,,action ,,of ,,prisms ,students in refraction--and one may still be a student after years of refracting--are sometimes puzzled as to just what a prism does when placed before an eye4 ,they refer to every available volume and are often confused between ductions and phorias1 finally dropping the subject as an unsolvable problem4 ,in view of this fact1 it is suggested that the refractionist should read the present volume with the actual instrument before him4 ,before proceeding1 one should first understand the effect of a prism and what it accomplishes4 ,to determine this1 close one eye1 looking at some small1 fixed object2 at the same time1 hold a ten degree prism base in before the open eye1 noting displacement of the object4 ,this will clearly show that the eye behind the prism turns toward the prism apex4 ,to carry the experiment further1 the following test may be employed on a patient4 ,covering one eye1 direct his attention to a fixed object1 placing the ten degree prism before the eye1 but far enough away to see the patient's eye behind it4 ,as the prism is brought in to the line of vision1 it will be seen that the eye turns towards the apex of the prism4 ,when the prism is removed1 the eye returns to its normal position4 ,similar experiments enable the refractionist to make the most practical use of treating phorias and ductions1 as well as to comprehend all other technical work4 ,illustration3 ,fig4 #ac--;,an important part of the equipment for muscular work4 ,,the ,,phorometer ,as previously stated1 it is practically impossible to accurately diagnose a case of muscular imbalance with trial-case prisms4 ,for this reason the phorometer forms an important part of the equipment for muscle testing in the ,ski-optometer1 having proven both rapid and accurate4 ,it consists of two five-degree prisms with bases opposite1 each reflecting an object toward the apex or thin edge4 ,the patient whose attention is directed to the usual muscle-testing spot of light1 will see two spots4 ,aside from the instrument itself1 and in further explanation of the phorometer's principle and construction1 when two five-degree prisms are placed together so that their bases are directly opposite1 they naturally neutralize2 when their bases are together1 their strength is doubled4 ,thus while the prisms of the phorometer are rotating1 they give prism values from plano to ten degrees1 the same being indicated by the pointer on the phorometer's scale of measurements4 ,as a guide in dark-room testing1 it should be noted that the handle of the phorometer in a vertical position is an indication that the vertical muscles are being tested2 if horizontal1 the horizontal muscles are undergoing the test4 ,,the ,,maddox ,,rod ,the ,maddox rod 7,fig4 #ad7 consists of a number of red or white rods1 which cause a corresponding colored streak to be seen by the patient4 ,this rod is placed most conveniently on the instrument1 being provided with independent stops for accurately setting the rods at #ij or #ahj degree positions4 ,the ,maddox rod has proven of valuable assistance in detecting muscular defects1 particularly when used in conjunction with the phorometer4 ,thus employed1 it enables the patient to determine when the streak seen with one eye crosses through the muscle-testing spot-light observable by the other eye1 as hereafter described4 ,illustration3 ,fig4 #ad--,the ,maddox ,rod1 a valuable aid in making muscular tests4 ,,procedure ,,for ,,making ,,the ,,muscle ,,test ,the ,ski-optometer should be equipped with two ,maddox rods1 one red and one white4 ,their combined use is of the utmost importance since they assist in accurately determining cyclophoria and its degree of tortion as designated on the degree scale1 and fully described in a later chapter4 ,when the ,maddox rods are placed in a vertical position1 it is an indication that the vertical muscles are being tested2 when placed horizontally1 the horizontal muscles are being tested4 ,it should be particularly noted that the streaks of light observable through the ,maddox rods always appear at right angles to the position in which they lie4 ,the ,ski-optometer should be placed in a comfortable position before the patient's face with the brow-rest and pupillary distance adjusted to their respective requirements4 ,the instrument should be levelled so that the bubble of the spirit level lies evenly between its two lines1 thus insuring horizontal balance4 ,the muscle test light should be employed at an approximate distance of twenty feet on a plane with the patient's head4 ,best results in muscle testing are secured through the use of the ,woolf ophthalmic bracket1 with iris diaphragm chimney and a specially adapted concentrated filament electric lamp 7,fig4 #i74 ,this gives a brilliant illumination which is particularly essential4 ,the test for error of refraction should be made in the usual manner1 using the spherical and cylindrical lenses contained in the ,ski-optometer1 thus obviating the transference of trial-case lenses and the use of a cumbersome trial-frame4 ,the time-saving thus effected enables the refractionist to include a muscle test in every examination and without tiring the patient--a consideration of the utmost importance4 ,,binocular ,,and ,,monocular ,,test ,the test for muscular imbalance may be divided in two parts4 ,first1 binocular test1 or combined muscle test of the two eyes2 second1 monocular test1 or muscle test of each eye separately4 ,the latter does not signify the shutting out of vision or closing off of either eye1 since muscular imbalance can only be determined when both eyes are open4 ,these two tests are fully explained in the following chapter4 ,,chapter ,,vii ,,the ,,binocular ,,muscle ,,test ,,made ,,with ,,the ,,maddox ,,rod ,,and ,,phorometer ,directing the patient's attention to the usual muscle testing spot of light1 the red ,maddox rod should be placed in operative position before the eye1 with the single white line or indicator on red zero 7,fig4 #ae74 ,the rods now lie in a vertical position4 ,illustration3 ,fig4 #ae--,the ,maddox rods placed vertically denote test for right or left hyperphoria1 causing a horizontal streak to be seen by patient4 ,the pointer of the phorometer should likewise be set on the neutral line of the red scale1 causing the handle to point upward 7,fig4 #af74 ,a distance point of light and a red streak laying in a horizontal position should now be seen by the patient4 ,illustration3 ,fig4 #af--,the phorometer handle placed vertically1 denotes vertical muscles are undergoing test for right or left hyperphoria--as indicated by 8,r4 ,h40 or 8,l4 ,h40 ,instead of memorizing a vast number of rules essential where trial case prisms are employed for testing ocular muscles1 the pointer of the phorometer indicates not only the degree on the red scale1 but the presence of right hyperphoria 7,r4 ,h47 or left hyperphoria 7,l4 ,h474 ,illustration3 ,fig4 #ag--,the horizontal streak caused by ,maddox rod bisecting muscle testing spot-light for vertical imbalance1 as patient should see it4 ,assuming that the patient finds that the streak cuts through the point of light1 the refractionist instantly notes the absence of hyperphoria4 ,should the point of light and the red streak not bisect1 prism power must be added by rotating the phorometer's handle to a position that will cause the streak to cut through the light 7,fig4 #ag74 ,while testing for hyperphoria1 the red scale should alone be employed1 the white scale being totally ignored4 ,illustration3 ,fig4 #ah--,the ,maddox rods placed horizontally test esophoria or exophoria1 causing a vertical streak to be seen by the patient4 ,,esophoria ,,and ,,exophoria ,the next step is to set the white lines of the red ,maddox rod either at white zero1 or #ahj line1 with the rods in a horizontal position 7,fig4 #ah7 and the phorometer on the white neutral line1 with handle horizontal 7,fig4 #ai71 thus making the test for esophoria or exophoria1 technically known as lateral deviations4 ,the red streak will now be seen in a vertical position4 ,should it bisect the spot of light1 it would show that no lateral imbalance exists4 ,should it not bisect1 the existence of either esophoria or exophoria is proven1 necessitating the turning of the phorometer handle4 ,should the refractionist rotate the handle in a direction opposing that of the existing imbalance1 the light will be taken further away from the streak1 indicating that the rotation of the prisms should be reversed4 ,illustration3 ,fig4 #ai--,the phorometer handle placed horizontally denotes horizontal muscles are undergoing test for esophoria or exophoria indicated by 8,es40 or 8,ex40 ,at the point of bisection 7,fig4 #bj71 the phorometer will indicate on the white scale whether the case is esophoria or exophoria and to what amount4 ,in testing esophoria 7,,es7 or exophoria 7,,ex71 the white scale is alone employed1 no attention being given to the red scale4 ,illustration3 ,fig4 #bj--,the vertical streak bisecting muscle testing spot-light for horizontal imbalance1 as patient should see it4 ,,making ,,muscle ,,test ,,before ,,and ,,after ,,optical ,,correction ,it is considered best to make the binocular test before regular refraction is made1 making note of the findings2 and again repeating the test after the full optical correction has been placed before the patient's eye4 ,this enables the refractionist to definitely determine whether the correction has benefited or aggravated the muscles4 ,furthermore1 by making the muscle test before and after the optical correction1 a starting point in an examination is frequently attained4 ,for example1 where the phorometer indicates esophoria it is usually associated with hyperopia1 whereas exophoria is usually associated with myopia1 thus serving as a clue for the optical correction4 ,assuming for example that the binocular muscle test shows six degrees of esophoria without the optical correction1 and with it but four degrees1 it is readily seen that the imbalance has been benefited by the optical correction4 ,under such conditions it is safe to believe that the optical correction will continue to benefit as the patient advances in years1 tending to overcome muscular defect4 ,,when ,,to ,,consider ,,correction ,,of ,,muscular ,,imbalance ,in correcting an imbalance1 it is also a good plan to adhere to the following rule3 ,in case of hyperphoria1 either right or left1 consider for further correction only those cases that show one degree or more4 ,in exophoria1 those showing three degrees or more4 ,in esophoria1 correct those showing five degrees or more1 except in children1 where correction should be made in cases showing an excess of #c of esophoria4 ,these rules are naturally subject to variation according to the patient's refraction and age1 but they are generally accepted as safe4 ,,four ,,methods ,,for ,,correction ,,of ,,muscular ,,imbalance ,there are four distinct methods for correcting muscular imbalance1 each of which should be carried out in the following routine3 #a4 ,optical correction made with spheres or cylinders1 or a combination of both4 #b4 ,muscular exercising or 8ocular gymnastics40 ,this is accomplished on the same principle as the employment of other forms of exercises1 or calisthenics4 #c4 ,the use of ,prisms3 ,when the second method fails1 prisms are supplied1 with base of prism before the weak muscle1 for rest only4 #d4 ,operation3 ,if the above three methods1 as outlined in the following chapters1 have been carefully investigated1 nothing remains but a tetonomy or advancement1 or other operative means for relief and satisfaction to the patient4 ,,the ,,rotary ,,prism ,the rotary prism of the ,ski-optometer1 7,fig4 #ba7 consists of a prism unit1 having a total equivalent of thirty degrees4 ,it is composed of two fifteen-degree prisms1 back to back1 so that the turn of its pinion or handle causes each of its lenses to revolve1 one on the other4 ,when its bases are opposite1 they neutralize2 when directly together1 they give a total value of thirty degrees4 ,while revolving from zero to maximum strength1 they give prism values which are indicated on the scale of measurements1 the red line denoting the total prism equivalent4 ,illustration3 ,fig4 #ba--,turning rotary prism's pinioned handle gives prism value from zero to #cj as indicated by prism's red line indicator4 ,it is obviously essential to know where the base of the rotary prism is located4 ,therefore if prism in or out is desired1 the zero graduations should be placed vertically and the red line or indicator set at the upper zero 7,fig4 #ba74 ,a rotation inward to #aj would give a prism equivalent of ten degrees1 base in4 ,a rotation from zero to #aj outward would give a prism equivalent of ten degrees1 base out1 etc4 ,with zero graduations horizontal and the red line or indicator set therewith1 a rotation upward to ten on the scale would give a prism equivalent of ten degrees1 base up4 ,a rotation from zero downward to #aj would give a prism equivalent of ten degrees1 base down4 ,an understanding of the foregoing will show that a rotation of the red line1 or indicator1 will give prism value from zero to #cj1 with base up1 down1 in or out4 ,,use ,,of ,,the ,,rotary ,,prism ,,in ,,binocular ,,muscle ,,tests ,should a case be one of esophoria1 exceeding the ten degree range of the phorometer1 the rotary prism should be brought into operative position with cypher 7#j7 graduations vertical 7,fig4 #ba71 while the red line or indicator should be set at #aj on the outer or temporal scale4 ,the phorometer's indicator should again be set on the center or neutral line on the white scale4 ,the rotary prism will then add ten degrees to the esophoria reading indicated on the phorometer4 ,should the case be one of exophoria1 exceeding ten degrees1 the indicator should be set at ten degrees upon the inner or nasal scale and the indicator of the phorometer should then be set at the white center or neutral line1 as in the previous test4 ,should prism power ever be required to supplement the phorometer in hyperphoria1 the rotary prism should be employed with zero graduations horizontal1 and the red line or indicator set at ten degrees on upper or lower scale1 as required4 ,,chapter ,,viii ,,the ,,monocular ,,duction ,,muscle ,,test ,,made ,,with ,,both ,,rotary ,,prisms ,while the previously described binocular muscle test made with the phorometer and ,maddox rod1 only determines the existence and amount of esophoria1 exophoria1 and hyperphoria1 neither the faulty nor the deviating muscle is located1 hence a monocular muscle test is essential in order to determine whether the muscles of the right or left eye are faulty4 ,furthermore1 an imbalance may possibly be due to either a faulty muscular poise1 or lack of nerve force in one or both eyes4 ,a 8duction test0 should accordingly be made of each muscle of each eye separately1 followed by a comparison of the muscular pull of both eyes collectively4 ,these tests are commonly termed adduction1 abduction1 superduction and subduction1 and are defined in the order named4 ,they include tests of the vertical and horizontal muscles of each eye1 made individually by means of the rotary prisms1 each being placed before the eye undergoing the test4 ,,locating ,,the ,,faulty ,,muscle ,the phorometer and the ,maddox rod should be removed from operative position1 discontinuing the use of the muscle-testing spot-light1 employed in the previously described binocular test4 ,the optical correction1 if one is required1 should be left in place1 while the patient's attention should be directed1 with both eyes open1 to the largest letter on the distant test chart2 or if preferable1 the ,greek cross in the ,woolf ophthalmic1 chimney may be used4 ,either one1 however1 should be located on a plane with the patient's head4 ,as a guide for the operator1 it might be well to remember that when the handle of the rotary prism is in a horizontal position1 the lateral or horizontal muscles are being tested4 ,on the other hand1 when the handle is in a vertical position1 the vertical muscles are undergoing the test4 ,,adduction ,adduction1 or relative convergence1 is the power of the internal muscles to turn the eyes inward2 prism power base out and apex in1 is employed4 ,illustration3 ,fig4 #bb--,to test adduction1 base out is required4 ,rotary prism's line or indicator should be rotated from zero outwardly4 ,to test abduction1 base in is required4 ,indicator should be rotated inwardly from zero4 ,to test adduction of the patient's right eye1 the rotary prism should be placed in position before the right eye1 the red line or prism indicator being registered at zero upon the prism upper scale4 ,the two cyphers 7#j7 should be placed in a vertical position with the handle pointed horizontally 7,fig4 #ba74 ,the rotary prism should then be rotated so that its red line or indicator is rotated outward from zero until the large letter--preferably the largest letter1 which is usually 8,e0--on the distance test-type or the ,greek cross previously referred to1 first appears to double in the horizontal plane4 ,the reading on the scale of measurements should accordingly be noted4 ,this test should be repeated several times1 constantly striving for the highest prism power that the patient will accept without producing diplopia4 ,the prism equivalent thus obtained will indicate the right adduction and should be so recorded1 as designated in ,fig4 #bd4 ,the amount of adduction ranges from #f to #bh1 prism diopters1 the normal average being #bd4 ,,abduction ,abduction is the relative power of the external muscles to turn the eyes outward4 ,prism power base in and apex out is employed4 ,to determine abduction1 or the amount of divergence of the external rectus muscle of the right eye1 prism power with base in or toward the nasal side should be employed4 ,the rotary prism will therefore remain in the same relative position as in making the adduction test 7,fig4 #bb71 with the two cyphers 7#j7 or zero graduations vertical1 but the indicator or red line should be rotated inward from zero1 or towards the patient's nose4 ,with the patient's attention again directed to the large letter 8,e10 or the ,greek cross1 this inward rotation should be continued until diplopia or double vision occurs4 ,like the former1 this test should be repeated several times1 the refractionist continuing to strive for the highest prism power which the eye will accept4 ,this will indicate abduction of the right eye and should be so recorded as designated in ,fig4 #bd4 ,the amount of abduction ranges from #c to #aj prism diopters4 ,the normal average is #h4 ,the ratio of adduction to abduction is normally rated at about three to one4 ,in other words1 it is conceded that the power of the eye to converge is normally three times as great as its power to diverge1 the usual measurements being eight to twenty-four respectively4 ,while applicable in most instances1 this may vary in different cases4 ,,superduction ,superduction1 sometimes termed sursumduction1 is the relative power of the superior recti to turn the eyes upward4 ,prism power base down and apex up is employed4 ,to test superduction1 the rotary prism should be placed in position with the two cyphers lying horizontally1 with the handle pointed vertically 7,fig4 #bc74 ,the patient's attention should again be directed to the large letter 8,e01 and the indicator or red line should be rotated downward from zero4 ,the highest prism power that the patient will accept before the object appears to double in the vertical plane will indicate the degree of right superduction4 ,this should be recorded accordingly4 ,conditions of this kind do not usually exceed two or three degrees4 ,the test1 however1 should be repeated several times before the final result is recorded1 as indicated in ,fig4 #bd4 ,the amount of superduction ranges from #a to #d prism diopters4 ,the normal average is #b4 ,illustration3 ,fig4 #bc--,to test superduction1 base down is required4 ,rotary prism's line or indicator should be rotated downward from zero4 ,to test subduction1 base up is required4 ,indicator should be rotated upward from zero4 ,,subduction ,subduction1 sometimes termed infraduction or deorsumduction1 is the relative power of the inferior recti to turn the eyes downward4 ,prism power base up and apex down is employed4 ,to test subduction1 the rotary prism should be operated with zero graduations placed horizontally1 as in the superduction test 7,fig4 #bc71 but the indicator should be slowly rotated in the reverse direction1 or upward from zero4 ,with the patient's attention again directed to the large letter 8,e10 or the ,greek cross1 the strongest degree prism thus secured without diplopia will indicate the right subduction4 ,the amount of subduction ranges from #a to #d prism diopters4 ,the normal average is #b4 ,any difference between superduction and subduction1 usually denoting the existence of hyperphoria1 should be given careful consideration4 ,,procedure ,,for ,,monocular ,,muscle ,,testing ,as previously explained1 after a duction test of each of the four muscles of the right eye1 the rotary prism before that eye should be placed out of position and the procedure for adduction1 abduction1 superduction and subduction repeated by means of the rotary prism before the left eye4 ,in case of an existing imbalance1 after testing the muscle of both right and left eyes1 the refractionist can quickly determine which muscle or muscles may be lacking in strength 7,fig4 #bd74 ,in practically every instance muscle exercises or correcting prisms may then be prescribed with definite knowledge of requirements1 as further described in the following paragraphs4 ,a binocular muscle test made with the phorometer1 ,maddox rod and distant muscle-testing point of light might quickly indicate six degrees of exophoria1 both before and after the optical correction is made4 ,while this would doubtless be the correct amount of the manifest imbalance1 it would be a difficult matter to ascertain which muscles caused the disturbance4 ,to determine this important question1 the monocular or duction test should be invariably employed4 ,,diagnosing ,a ,,specific ,,muscle ,,case ,assuming1 for example1 a specific case where six degrees of exophoria was determined in the binocular test that the muscle findings in the duction test show right adduction of twenty-four degrees1 with an accompanying abduction of eight degrees2 likewise a superduction and subduction of two degrees for each eye4 ,with the aid of a chart or diagram--which should be made in every case--a comparison of these figures would indicate an exophoria of approximately six degrees1 with a corresponding weak left internus 7,fig4 #bd74 ,this not only shows the muscle pull of each eye individually1 but a comparison of the two eyes as indicated by the dotted lines4 ,thus the relationship of the two eyes1 and their corresponding muscles is quickly indicated4 ,illustration3 ,fig4 #bd--;,duction chart should be made in every case4 ,above readily shows existence of muscular imbalance and proves subduction and superduction for both eyes are equal2 otherwise hyperphoria would be disclosed4 ,also note abduction for both right and left eye are equal1 otherwise esophoria would be disclosed4 ,also note adduction for right eye is #bd while left is but #ah1 proving a case of #f of exophoria with a left weak internus4 ,a glance at the above diagram discloses the following three important facts1 all of which should be known to the refractionist before a single thought can be devoted to the correcting of the case3 #a4 #f exophoria is the amount of the insufficiency4 #b4 #ah adduction 7which should be #bd74 #c4 ,left weak internus4 ,as previously stated1 the power to converge is normally rated #c to #a1 or #h to #bd1 as shown above1 while the power of the eye to look upward1 is equal to the power to look downward4 ,the diagram accordingly proves that the muscles of the right eye are in perfect balance1 having equal muscular energy4 ,a comparison of the left eye shows adduction of #ah degrees with an abduction of #h degrees1 proving a lateral insufficiency because the ratio is less than #c to #a2 and the muscles of the left eye are at fault4 ,the power of #b degrees superduction and #b degrees subduction1 proves that no weakness exists in the vertical muscles4 ,after making the duction test for each eye individually1 a comparison of both eyes in relationship to each other may be more readily determined by following the dotted lines 7,fig4 #bd74 ,as previously stated1 it is the inability of the two eyes to work together that causes the imbalance1 so that if both eyes were normal1 the adduction1 abduction1 superduction and subduction of the two eyes would agree4 ,the duction chart 7,fig4 #bd47 also shows that the corresponding muscles of each eye agree--with the exception of the adduction of the right eye and the left eye4 ,this proves that the left internus is weak1 measuring only #ah degrees instead of #bd degrees2 it further proves the #f degrees of exophoria in the monocular test1 as was quickly and more readily determined in the binocular test4 ,likewise1 in cases of esophoria1 hyperphoria1 or cataphoria1 the making of definite muscle measurements independently through the prescribed method would show through the merest glance at a similar diagram which muscle or muscles were relatively out of balance4 ,heterphoria of almost any type1 or tendencies other than normal1 may be fully investigated by making a thorough and separate test of each muscle4 ,where an imbalance exists1 a rapid test may be employed to distinguish a pseudo or false condition from a true condition4 ,this is accomplished by first placing the two ,maddox rods 7both the red and white7 so that the rods lie in a vertical position4 ,if the two lines fuse1 we have determined the existence of a false condition caused by a possible error of refraction or nerve strain4 ,if the lines separate1 we have determined a true muscular condition1 and then only should the second method of muscular treatment follow4 ,illustration3 ,same as ,model #bae but ,automatic ,cylinder ,arrangement omitted4 ,,ski-,,optometer ,,model #bje ,embodying ,spherical ,lenses ,combined with ,appliances for ,testing and ,correcting ,muscular ,imbalance4 ,,chapter ,,ix ,,first ,,method ,,of ,,treatment ,,optical ,,correction ,the mere determination of the degree of an imbalance1 or even the diagnosis of a patient's trouble1 is not sufficient4 ,if relief is to be secured1 something more must be accomplished4 ,as previously stated1 muscular imbalance may be corrected through one of the four following rules or methods1 each explained in their relative order3 #a--,optical ,correction #b--,muscular ,exercise #c--,use of ,prism ,lenses #d--,operative ,methods ,,esophoria ,to correct a case of muscular imbalance1 where six degrees of esophoria has been determined1 the first rule of making the test for optical correction with the ,ski-optometer's spherical and cylindrical lenses1 would be in the line of routine4 ,the binocular test made with the phorometer and combined use of the red ,maddox rod would have determined the six degrees of esophoria4 ,the reason for making the binocular muscle test before and after the optical correction is because an imbalance is often aggravated or benefited by the correcting lenses4 ,the optical correction frequently eliminates the need for further muscular treatment4 ,for example1 we will assume that the optical correction tends to decrease the degree of esophoria from six degrees to four degrees4 ,according to the previously mentioned rule for correcting cases exceeding one degree in hyperphoria1 three degrees in exophoria and five degrees in esophoria1 the condition would indicate that of being 8left alone40 ,just what is taking place should be fully understood--its cause as well as its effect4 ,illustration3 ,fig4 #be--;,comparative diagram showing how a decentered lens before a centered eye has the same effect as a centered lens before a decentered eye4 ,when not otherwise specified1 accurately centered lenses are of primary importance4 ,the pupil of the eye should be directly behind the center of each lens 7,fig4 #be74 ,figure 8,a0 of the latter sketch illustrates a perfectly centered lens--its center indicated by a cross1 the circle representing an eye directly behind it4 ,figure 8,b0 illustrates a perfectly centered pupil behind a prism1 with its center designated by a cross4 ,to ascertain how the centered spherical lens takes the place of a prism1 ,figure 8,c0 should be compared with ,figure 8,b02 this will show that the eye is decentered1 while the lens is centered4 ,a further comparison will prove that the results in ,figures 8,b0 and 8,c0 are identical1 the correcting lenses having practically the same effect through the decentration of the eye as if a prism were prescribed1 nature supplying its own decentration4 ,,treatment ,,for ,,correcting ,,esophoria ,,in ,,children ,in case of esophoria1 regardless of amount1 slightly increased spherical power is frequently prescribed for children4 ,this will naturally blur or fog the patient's vision1 but in their effort to overcome the blur1 accommodation is relaxed1 usually tending to correct the muscular defect4 ,in such cases1 as a rule1 a quarter diopter increased spherical strength may frequently be added for each degree of esophoria as determined before the optical correction was made4 ,in a case of #f degrees of esophoria1 the refractionist may prescribe #a4ej diopter spherical added to the optical correction1 which1 let us assume1 is #a4jj sph4 -#a4jj cyl4 ax4 #ahj1 so that the treatment glasses would be #b4ej sph4 -#a4jj ax4 #ahj 7,see ,procedure on ,page #gd74 ,at the end of each three months' period1 the patient should be requested to return1 when the binocular and the duction test should again be made1 comparing results with the work previously accomplished4 ,an improvement tending to build up the left weak externus will possibly permit of a decrease of the excessive spherical power1 so that excessive spherical power is reduced until completely removed1 in all probability overcoming the muscular defect4 ,esophoria is almost invariably a false condition and frequently is outgrown under this treatment as the child advances in years4 ,on the other hand1 esophoria uncared for in the child may tend to produce exophoria in the adult4 ,,how ,,optical ,,correction ,,tends ,,to ,,decrease #f ,,esophoria ,,in ,a ,,child ,illustration3 ,assume binocular muscle test made before optical correction shows #f ,esophoria4 #a4 ,sph4 -#a4 ,cyl4 ,ax4 #ahj4 ,next1 locate faulty muscle by making a duction test1 which shows how abduction of left eye is made to equal that of right eye1 change being made quarterly with treatment lenses in accordance with following rule4 ,note as abduction is increased1 esophoria is reduced4 ,rule--prescribe a quarter diopter increased sphere for each degree of imbalance or #j4be #f equals3 #a4ej added to optical correction4 #a_/a_/ai 7assumed date7 prescribed treatment lenses equal3 #b4ej -#a4 #ahj4 #d_/a_/ai 7#c months later7 assuming abduction has increased from #b to #c showing difference of #e ,es4 or #j4be #e4 equals #a4be added to optical correction1 prescribed treatment lenses equal3 #b4be -#a4 #ahj4 #g_/a_/ai 7#c months later71 assuming abduction has increased from #c to #d showing difference of #d ,es4 or #j4be #d equals #a4jj which added to optical correction would make prescribed treatment lenses equal3 #b4jj -#a4 #ahj4 ,and so on1 every three months treatment lenses are prescribed until both right and left eye show #h of abduction4 ,in this way the treatment lenses are reduced to original correction of #a4jj -#ajj #ahj4 ,this would have required six changes of lenses1 three months apart--thus consuming #ah months time4 ,,chapter ,x ,,second ,,method ,,of ,,treatment--,,muscular ,,exercise ,,made ,,with ,,two ,,rotary ,,prisms ,,and ,,red ,,maddox ,,rod ,,exophoria ,if a case is one of exophoria of six degrees1 where the second method of treatment or muscular exercise is in line of routine1 it is essential to first determine through a duction test and the preparation of the diagram exactly which one of the four muscles are faulty 7,fig4 #bd74 ,having determined1 with the aid of the diagram1 first1 the existence of #f degrees of exophoria2 second1 #ah degrees of adduction2 third1 a weak left internus--the next procedure is to determine what degree of prism will enable the patient to obtain single binocular vision1 with both eyes looking 8straight40 ,to determine this1 place both of the ,ski-optometer's rotary prisms in position with the handle of each pointing outward horizontally4 ,the red line or indicator of each prism should then be placed at #cj of the outer scale 7,fig4 #bf74 ,the red ,maddox rod should be horizontally positioned before the eye1 the white line on indicator pointing to #ahj of the scale 7,fig4 #bg74 ,the strength of the rotary prism before the right eye should thereupon be reduced by rotating the prism indicator or red line toward the upper zero 7#j7 to a point where the patient first sees the red streak--assuming that the red line appears at #db degrees1 that is #cj degrees before the left eye and #ab degrees before the right4 ,illustration3 ,fig4 #bf 7,a and ,b7--,first position of rotary prisms to determine amount of prism exercise to be employed for building up the weak muscle4 ,the prism should then be still further reduced until the vertical streak produced by the ,maddox rod directly bisects the muscle testing spot of light4 ,assuming that this point be thirty-eight degrees1 which is four degrees less1 single binocular vision is produced4 ,illustration3 ,fig4 #bg--,position of red ,maddox rod used in conjunction with ,fig4 #bf for prism exercising4 ,for example1 sixty degrees of prism power 7the combined power of the two rotary prisms7 will usually cause complete distortion4 ,therefore1 as outlined in ,figure #bh1 the patient1 seeing only out of the right eye1 will detect nothing but a white light4 ,by gradually reducing the strength of the prism before the right1 which is the good eye1 the patient will eventually see a red streak off to the left4 ,a continued and gradual reduction to a point where the red streak bisects the white light1 will determine how much prism power is required for the patient to obtain single binocular vision1 thus establishing the same image at the same time on each fovea or retina 7,fig4 #bj74 ,this has taught the patient to do that which he has never before accomplished4 ,therefore1 after having been taught how to make the two eyes work in relation to each other1 the natural tendency thereafter will be to strive for the same relationship of vision with both eyes4 ,the refractionist should then aim to reduce the excessive amount of prism required to give binocular vision1 which can be accomplished by muscular exercise4 ,it must always be remembered before the refractionist is ready to employ the muscular exercise or second method1 that the degree of prism required to give the patient single binocular vision must be determined with the optical correction in place4 ,the exercise must be practised daily in routine1 a daily record being essential4 ,,an ,,assumed ,,case ,we will assume a case where #db degrees is required to enable the patient to first see the red streak as produced by the ,maddox rod to the extreme left4 ,through a continued gradual reduction of #d degrees 7or to #ch degrees71 we next learn that the streak was carried over until it bisected the white spot of light1 giving single binocular vision and producing a position of rest4 ,illustration3 ,fig4 #bh--,simplified chart showing the prism action employed in developing a weak ocular muscle through alternating prism exercise4 ,either side of #ch in excess of #d causing diplopia4 ,the patient has now established the limitation of the exercise1 which is four degrees1 this limitation being determined by the difference between the point where the streak was first seen to the extreme side and where it bisected the spot4 ,the same amount of four degrees should then be used for the opposite side1 thus reducing the prism strength to #cd degrees4 ,this again produces diplopia1 because of the lesser amount of prism power employed to give single binocular vision4 ,the refractionist should then return to #ch degrees1 where single binocular vision had originally been determined 7,fig4 #bh71 alternating back to #db1 returning to #ch1 over to #cd1 back to #ch1 and so on4 ,this procedure should be employed once a day just after meals for about five minutes1 and repeated ten times1 constantly striving for a slight reduction of prism power from day to day4 ,,effect ,,of ,,muscular ,,exercise ,this muscular treatment1 or constructive exercising1 should enable the patient to overcome his amount of four degrees in either direction in about a week4 ,hence in the case showing #ch degrees for single binocular vision1 results may be looked for in about nine weeks--four degrees divided into #ch degrees4 ,while the patient is undergoing the treatment1 which is nothing more than the strengthening of the interni muscles or developing adduction1 it is natural to believe that the amount of imbalance is likewise being conquered4 ,this1 however1 is readily determined from time to time by making the binocular muscle test with the phorometer and ,maddox rod1 as well as the duction chart test 7,fig4 #bd71 as previously outlined4 ,to fully appreciate the effect of this muscular treatment1 the reader need only hold his head in a stationary position1 casting his eyes several times from the extreme right to the extreme left1 not failing to note the apparent muscular strain4 ,on the other hand1 with the aid of the ,ski-optometer's rotating prisms1 the refractionist not only has complete control of the patient's muscles at all times1 but scientifically accomplishes muscular exercise without any tiresome strain1 overcoming all possible exertion4 ,after the case in question has been reduced to #cj degrees1 having no further use for the rotary prism1 it may be removed from before the right eye and the same exercising procedure continued as before with the remaining left side rotary prism by reducing its power1 until it is likewise down to zero4 ,having reduced both prisms to zero1 each prism should again be placed in position with zero graduations vertical and the prism indicator on upper zero4 ,both prisms should then be turned simultaneously about four degrees toward the nasal side of the patient1 thus tending to jointly force corresponding muscles of both eyes4 ,,home ,,treatment ,,for ,,muscular ,,exercise--,,square ,,prism ,,set ,,used ,,in ,,conjunction ,,with ,,the ,,ski-,,optometer ,where a patient is unable to call each day for this muscular treatment or exercise1 the work will be greatly facilitated by employing a specially designed set of square prisms ranging in strength from to #bj degrees for home treatment4 ,as in the case previously cited1 it is necessary to carefully instruct the patient that the interni muscles must be developed1 hence prism base out with apex in must be employed4 ,attention should then be directed to a candle light1 serving as a muscle testing spot of light and stationed in a semi-dark room at an approximate distance of twenty feet4 ,having determined through the ,ski-optometer the strength of the prism required after each office treatment1 its equivalent should then be placed in a special square prism trial-frame which permits rotation of the prism1 although the patient is frequently taught to twirl the lens before the eye4 ,this exercise may be continued for about five minutes each day4 ,the patient should also be instructed to call at the end of each week1 when the work may be checked by means of the ,ski-optometer's rotary prisms1 making the duction test as previously explained and outlined in ,fig4 #bd4 ,it is then possible to determine whether or not satisfactory results are being obtained4 ,otherwise the exercise should be abandoned4 ,should the second method employed in the work of muscular imbalance not prove effective1 the third method requiring the use of prisms would be next in routine4 ,,chapter ,,xi ,,third ,,method ,,of ,,treatment--,,prism ,,lenses ,,when ,,and ,,how ,,employed ,as stated in the preceding chapter1 on ascertaining the failure of the second muscular treatment or method1 prisms are employed for constant wear4 ,when prism lenses are used1 whether the case is exophoria or esophoria1 or right or left hyperphoria1 it is always safe to prescribe one-quarter degree prism for each degree of prism imbalance for each eye4 ,for example1 in a case of #f degrees of esophoria1 a prism of #a degree base out should be prescribed for each eye2 or in #f degrees of exophoria1 employ the same amount of prism1 but base in4 ,in right hyperphoria1 place the prism base down before the right eye and up before the left1 and vice versa for left hyperphoria4 ,it is not always advisable1 however1 to allow the patient to wear the same degree of prism for any length of time4 ,many authorities suggest a constant change with the idea that a prism is nothing more than a crutch4 ,should the same degree be constantly worn1 even though it afforded temporary relief1 the eye would become accustomed to it and the purpose of the prism entirely lost4 ,prisms should be prescribed with extreme care1 their use being identical with that of dumb-bells1 where weight is first increased to maximum and subsequently reduced1 viz43 ,,prism ,,reduction ,,method ,where prisms are prescribed1 it is considered good practice to make a binocular muscle test and the duction test 7,fig4 #bd7 at the end of each three months' period1 employing the phorometer1 ,maddox rod1 and rotary prisms1 as already explained4 ,if the condition shows any decrease1 the prism degree should be proportionately decreased4 ,for example1 in the case originally showing #f degrees of exophoria1 one-quarter degree prism for each degree of imbalance was prescribed1 or #a degree for each eye4 ,if the same case subsequently indicated #d degrees1 only one degree for each eye should be prescribed--and so on1 a gradual reduction of prism value being constantly sought4 ,except in rare cases1 prisms should not be prescribed with the base or apex at oblique angles1 as the eye is rarely at rest with such a correction4 ,an imbalance may be caused by a false condition in one rectus and a true imbalance in the other1 giving one the impression that cyclophoria exists1 as explained in a following chapter4 ,having now employed the three methods1 the refractionist can readily understand that a marked percentage of muscular imbalance cases may be directly benefited through the aid of the ,ski-optometer4 ,if these three methods of procedure fail1 there is nothing left but the fourth and last method--that of operative procedure4 ,,chapter ,,xii ,a ,,condensation ,,of ,,previous ,,chapters ,,on ,,the ,,procedure ,,for ,,muscle ,,testing ,,with ,,the ,,ski-,,optometer ,the present chapter1 intended for those desiring a synopsis or condensed summary of muscular imbalance work1 should prove of the utmost assistance to the busy refractionist4 ,muscular imbalance work can be successfully conducted if the following routine is studied and memorized1 with the ,ski-optometer constantly before the reader4 ,the chapters containing the corresponding figures and diagrams or illustrations will then be readily comprehended4 ,it is also important to carefully note the captions under each diagram4 #a4 ,without any testing lenses before patient's eyes1 direct attention to a #bj-;foot distant muscle testing spot of light 7,fig4 #i74 #b4 ,place phorometer handle vertically 7,fig4 #af74 ,place red ,maddox rod vertically 7,fig4 #ae74 ,patient should see a white spot of light1 and a red horizontal streak 7,fig4 #ag74 ,simply turn phorometer handle until horizontal streak bisects white spot of light4 ,pointer then indicates amount of deviation on red scale4 ,ignore cases less than #a hyperphoria1 whether right or left designated by 7,r4 ,h4--,l4 ,h474 #c4 ,place phorometer handle horizontally 7,fig4 #ai74 ,place red ,maddox rod horizontally 7,fig4 #ah74 ,patient should see a white spot of light and a vertical red streak 7,fig4 #bj74 ,simply turn phorometer handle until red streak bisects spot of light4 ,pointer indicates amount of deviation on white scale1 whether esophoria or exophoria designated by 7,es--,ex74 #d4 ,ignore all exophoria cases1 less than #c4 ,ignore all esophoria cases1 less than #e--;except in children1 ignore less than #c of esophoria4 #e4 ,always make the above or binocular muscle test--with phorometer and red ,maddox before optical correction or 7test for spheres and cylinders7 and again after optical correction where case shows more than #a-c-e rule1 to determine whether muscles are aggravated or benefited4 #f4 ,in cases showing more than the #a-c-e rule1 shown in above ,no4 #d1 make monocular duction test first with rotary prism before patient's right eye1--then with rotary prism before left eye to find faulty muscle and determine which eye is affected4 #g4 ,to test adduction1 prism base out is required4 ,rotary prism's red line or indicator should be rotated from zero outwardly4 ,to test abduction1 base in is required4 ,indicator should be rotated inwardly from zero 7,fig4 #bb74 ,power of adduction as compared with abduction1 is normally #c to #a--usually rated #bd to #h4 #h4 ,to test superduction1 base down is required4 ,rotary prism's line or indicator should be rotated downward from zero4 ,to test subduction1 base up is required4 ,indicator should be rotated upward from zero4 ,power of superduction as compared with subduction1 is normally equal--usually rated #b for each 7,fig4 #bc74 #i4 ,direct patient's attention to largest letter on distant chart1 usually letter 8,e10 rotating red line indicator of rotary prism outlined in above ,no4 #g and ,no4 #h1 until diplopia is first procured4 #aj4 ,the use of a duction chart on a record card1 quickly designates pull for each of four muscles 7,fig4 #bd71 illustrating an assumed case of-- #ast--#f;,d of ,exophoria4 #bnd--#ah adduction 7which must be developed to #bd74 #crd--,patient has a left weak internus4 #aa4 ,employ ,first ,method--,optical ,correction--to effect treatment4 #ab4 ,assuming a case of a child with #f of esophoria--#h of right abduction and #b left abduction indicating a left weak externus1 prescribe a quarter diopter increased plus spherical power for each degree of imbalance1 thus adding #a4ej;,d spherical to optical correction4 ,this is the first method of treatment4 ,this requires a thorough reading of ,chapter ,,ix on ,treatment for ,correcting ,esophoria in ,children and a careful study of the formula4 ,for synopsis see ,page #gd4 ,,four ,,methods ,,of ,,treating ,,an ,,imbalance ,,case ,,when ,,the ,,preceding ,,one ,,fails #ast--,optical correction2 #bnd--,muscular exercise or treatment2 #ge ,,are ,,curable ,,with ,,first ,,and ,,second ,,methods4 #crd--,prisms2 #e ,,are ,,curable ,,with ,,third ,,method4 #dth--,operation2 #bj ,,are ,,curable ,,with ,,fourth ,,method4 #ac4 ,when first method of treatment fails1 ,,employ ,,second ,,method--,muscular ,exercise--to effect treatment4 #ast--,find degree of prism patient will accept to produce single binocular vision with optical correction on1 placing both rotary prisms in position1 handles horizontal1 red line on #cj of temporal scale of each1 giving total value to #fj 7,fig4 #bf;a and b74 #bnd--,also place red ,maddox rod before patient's eye 7rods horizontal7 7,fig4 #ah71 calling patient's attention to usual muscle testing spot of light4 #crd--,reduce prism before good eye until red streak appears1 noting degree 7which we assume shows #db the combined total value of both prisms7 slowly continue to decrease prism until streak bisects spot4 ,assume this shows total of #ch4 ,either side of #ch in excess of #d 7#ch to #db7 produces diplopia4 ,prisms must only be rotated from #ch to #db back to #ch over to #cd--;back to #ch over to #db--;back again to #ch and so on--exercise to be continued daily ten times for five minutes 7,fig4 #bh74 #dth--,at end of each week1 duction test should again be made4 ,duction chart should show a tendency to reduce exophoria by a gradual building up of adduction1 approximately one week is usually sufficient to teach patient to hold streak within the spot 7between #ch and #db74 ,exercise to be continued until both prisms are worked down to zero4 ,exercise tends to teach patient how to establish same image on each fovea or retina at same time4 #eth--,if patient is unable to call daily for treatment1 employ home treatment4 7,read 8,home ,treatment for ,muscular ,exercising10 ,page #hb74 ,employ ,,third ,,method--,use of ,prisms for ,constant ,wear to effect treatment4 ,,prisms #ast4 ,where a case cannot be reduced through use of first two methods1 as for example in a case of #f of exophoria1 prescribe of amount of imbalance 7 #f #a7 for each eye--base in--or esophoria base out1 hyperphoria base up on eye affected4 #bnd4 ,advise patient to call every three months and make duction test 7,fig4 #bd74 ,if no improvement in condition1 after wearing prisms six months1 operative means is suggested4 ,assume a case is benefited1 reduce prism power according to rule2 ,d prism for each degree of imbalance4 ,,cyclophoria ,this work being of a technical nature1 it is deemed best for the reader to study ,chapter ,,xiii and ,,xiv4 ,,chapter ,,xiii ,,cyclophoria ,,made ,,with ,,maddox ,,rods ,,and ,,rotary ,,prisms ,cyclophoria1 a condition affecting the oblique muscles of the eye1 is caused by its rotation4 ,it is detected in the following manner by the combined use of the red and white ,maddox rods and the rotary prism4 ,illustration3 ,fig4 #bi--,position of rotary prism for producing diplopia in testing cyclophoria with prism placed at #h base up4 ,darken the room and direct the patient's attention to the usual muscle-testing spot of light1 located approximately twenty feet away and on a direct plane with the patient's eye4 ,the optical correction1 if one is required1 should always be left in place--just as in making other previously described muscle tests4 ,the rotary prism should then be brought before the patient's right eye with the handle-pointing upward and with zero graduations horizontal4 ,the indicator or red line should then be rotated upward from zero to eight upon the prism scale1 creating the equivalent of a prism of #h diopters with base up 7,fig4 #bi74 ,this normally caused diplopia1 although in some cases it may be necessary to place the prism at #aj or #ab degrees before diplopia is produced4 ,illustration3 ,fig4 #cj--7;,a4 and ,b47--,first position of both ,maddox rods used in conjunction with ,fig4 #bi for determining cyclophoria4 ,the red ,maddox rod should then be brought into operative position before the patient's left eye 7,fig4 #cj;a7 and the white ,maddox rod before the patient's right eye1 7,fig4 #cj;b7 setting each one so that the rods lie in a vertical position with their white line on the large red zero 7#j74 ,the patient should now see two separate and distinct streaks of light1 one appearing below the other4 ,illustration3 ,,determining ,,cyclophoria ,,right ,,eye ,,left ,,eye ,fig4 #ca ,fig4 #cd ,,no ,,cyclophoria ,,no ,,cyclophoria ,illustration3 ,fig4 #cb ,fig4 #ce ,,cyclophoria ,,cyclophoria ,illustration3 ,fig4 #cc ,fig4 #cf - ,,cyclophoria - ,,cyclophoria ,figs4 #ca-cf--;,diagram showing how streaks appear to patient1 as produced by the ,maddox rods in testing for cyclophoria4 ,should there be no cyclophoria of the right eye1 the streaks will appear in a horizontal plane parallel to each other 7,fig4 #ca74 ,should the red streak appear horizontally to the left eye1 and the white streak seen by the right eye appear at an angle therewith1 cyclophoria of the right eye would be indicated 7,fig4 #cb74 ,in brief1 should the white streak dip towards the patient's left side1 the case would be one of right plus cyclophoria 7,fig4 #cb72 whereas right minus cyclophoria would be indicated should the white streak dip to the patient's right side 7,fig4 #cc74 ,next1 setting the rotary prism of #h degrees1 placed base up before the patient's left eye1 the red streak should appear below the white one4 ,should the two streaks appear horizontally1 parallel with each other1 there would be no cyclophoria of the left eye 7,fig4 #cd74 ,if1 however1 the upper or white streak should appear horizontal1 and the lower or red streak at an angle therewith dipping toward the patient's right side1 the left eye would be cyclophoric and the case would be one of left plus cyclophoria1 as the chart indicates 7,fig4 #ce74 ,should the red streak dip in toward the patient's left side1 left minus cyclophoria would be designated 7,fig4 #cf74 ,the patient would instinctively describe1 with pointed finger and hand motion1 the position of the 8dipping0 line just as one would describe a spiral staircase4 ,should this test determine that no cyclophoria exists in either eye1 there would be no necessity for further tests4 ,some authorities claim that both ,maddox rods should be of the same color1 so as to more readily assist the patient to fuse the two objects4 ,if the reader so desires1 he can readily place a red lens from the trial-case in the forward cell of the instrument4 ,the characters plus and minus in cyclophoria merely refer to plus as signifying a tendency toward the temporal side2 minus indicating a tendency toward the nasal side4 ,this has no bearing on 8convex0 and 8concave10 which are frequently designated as 8plus0 and 8minus40 ,the test for cyclophoria is particularly essential1 proving of utmost importance where the patient requires an astigmatic correction with the cylinder axis in oblique meridian4 ,the case should then be investigated in every instance by making a thorough and separate test of each eye for cyclophoria4 ,in a case where cyclophoria is determined1 the trouble may be caused by the functioning of other muscles1 through the drain of nerve force1 thus disturbing the harmony of every muscle action4 ,cyclophoria is frequently caused by an imbalance of two recti1 giving an oblique pull4 ,in most cases1 it is merely necessary to release the torsion1 as described in the following chapter4 ,,chapter ,,xiv ,,cycloduction ,,test ,,made ,,with ,,the ,,combined ,,use ,,of ,,the ,,two ,,maddox ,,rods ,having determined that cyclophoria exists1 as previously outlined1 the next step would be to make a cycloduction test1 or a test of the oblique muscles individually4 ,maddox rods1 both red and white1 should be placed in position with the rods horizontal--the plus and minus sign at #ij degrees on the scale 7,fig4 #cg74 ,the patient's attention should be directed to the usual muscle-testing spot of light1 when a vertical band of light will appear to the patient1 as shown in ,fig4 #ch4 ,illustration3 ,fig4 #cg--7;,a4 and ,b47--,primary position of combined use of both ,maddox rods for determining cycloduction test4 ,illustration3 ,,fig4 #ch ,,normal ,illustration3 ,,fig4 #ci ,,right ,,cycloduction ,,left -,,cycloduction ,illustration3 ,,fig4 #dj ,,right -,,cycloduction ,,left ,,cycloduction ,figs4 #ch-dj--;,diagram showing position of streaks produced by ,maddox rods as they appear to patients in making cycloduction tests4 ,to measure the duction range of the inferior oblique of the right eye1 it is merely necessary to slowly rotate the ,maddox rod before the right eye upward at its nasal end to the point where the band of light breaks so as to resemble a letter 8,x04 ,this gives in degrees the amount of right plus cycloduction1 as indicated on the temporal scale1 when it will appear to the patient1 as shown in ,fig4 #ci4 ,the ,maddox rod should then be restored to its original position1 with the plus and minus on the #ij degree line of the scale 7,fig4 #cg71 and rotated upward at the temporal end until it again takes the form of the letter 8,x04 7,fig4 #dj47 ,the position of the indicator will now denote the amount of right minus cycloduction1 or duction range of the right superior oblique muscles4 ,having determined the duction range of the oblique muscles of the patient's right eye1 both ,maddox rods should be placed in original position with rods horizontal and plus and minus sign on #ij of scale1 as shown in ,fig4 #cg4 ,the ,maddox rod before the left eye is then employed exactly in the same manner as before when the test for the right eye was made4 ,a plus cycloduction of the left eye would be indicated1 as shown in ,fig4 #dj1 while a minus cycloduction of the left eye would appear to the patient1 as shown in ,fig4 #ci4 ,by recording a comparison of each eye1 as explained1 it will be found that the range of duction usually averages five to twenty degrees on either side of the #ij degree line1 as indicated on the scale surrounding the ,maddox rods4 ,it will be recalled that cyclophoria was only to be looked for in oblique astigmatic cases4 ,it is frequently possible to correct the patient's trouble1 by changing the axis of the cylinder1 before one or both eyes1 a minus cycloduction signifying a change of axis towards #ahj while a plus toward #ij1 according to the amount lacking in full duction power4 ,it is also well to exercise the oblique muscles through a rotation of the ,maddox rod before the affected eye1 whether it be one or both that is lacking in full duction power1 until the required amount is reached to equal its fellow member4 ,for a more exhaustive treatise the author suggests a reading of ,dr4 ,savage's work on the subject4 ,,treatment ,,for ,,cyclophoria ,as previously stated1 it often proves of great benefit to employ a muscular exercise where a patient has an existing cyclophoria of either one or both eyes1 results derivable through the exercise of the recti muscles having been previously detailed4 ,to exercise the oblique muscles of the right eye1 both ,maddox rods should be placed in the original position employed for making cycloduction test1 as previously explained 7,fig4 #cg74 ,this causes the patient to see but one band or vertical streak 7,fig4 #ch74 ,the ,maddox rod1 placed before the right eye1 should be slowly rotated inward from ninety degrees to a point on the scale where the single streak of light breaks1 when it should again be returned to ninety degrees4 ,this causes a contraction and relaxation of the muscles in the form of an exercise and should be repeated ten times--about five minutes each day4 ,by employing the ,maddox rod before the left eye in precisely the same manner1 its oblique muscles will be exercised4 ,to determine whether or not this form of exercise is beneficial to the patient1 the weekly cycloduction test1 as previously described1 should be made and compared with the original findings4 ,illustration3 ,a ,compact ,phorometer and ,trial-,frame4 ,,ski-,,optometer ,,model #bce ,for ,testing and ,correcting ,muscular ,imbalance--,providing a ,comfortable ,form of ,trial-,frame4 ,,chapter ,,xv ,,movements ,,of ,,the ,,eyeballs ,,and ,,their ,,anomalies ,after a careful study of the foregoing chapters1 the refractionist may desire further knowledge concerning muscular imbalance--a matter in which the ,ski-optometer plays an exceptionally important part4 ,it should be remembered that it is only the general utility of the instrument1 plus one's knowledge of refraction and individual diagnosis that enables the refractionist to attain maximum efficiency in every examination1 a fact which largely accounts for the following chapter4 ,,monocular ,,fixation ,when we view an object directly1 so that it appears to be more distinct than surrounding objects1 we are said to 8fix0 or 8fixate0 it4 ,as the fovea is normally the most sensitive part of the retina1 affording by far the most distinct vision1 8fixation10 in the great majority of cases1 is so performed that the image of the object that is 8fixated0 falls upon the fovea of the eye that is 8fixing40 ,this is known as central or muscular 8fixation40 ,when central vision is absent1 however1 the patient is compelled to see with a portion of the retina outside of the fovea4 ,the eye must then be so directed as to cause the image of the object to fall on this outlying portion of the retina4 ,this is termed 8eccentric fixation10 and usually denotes that vision is exceptionally poor4 ,the ability to 8fix0 is apparently acquired in early infancy by constant practice in looking at objects4 ,any marked interference with vision1 particularly with central vision--present at birth or soon thereafter--will tend to prevent the acquisition of this ability1 and in extreme cases the eye does not learn to 8fix0 at all1 but aimlessly wanders in all directions4 ,,binocular ,,fixation ,we habitually use the eyes together1 fixating with both at once2 that is1 we direct the eyes in such a way that the image of the object to which the attention is directed falls on the fovea of each eye4 ,where both eyes are accurately directed to an object at which one or both are looking1 the condition is known as 8binocular fixation10 which is commonly understood to mean that both eyes are straight4 ,the ability to produce and maintain binocular fixation--to keep both eyes directly straight--is acquired early in life4 ,the impulse to maintain it grows with exercise1 and soon becomes so strong that after the age of infancy binocular fixation is present in the great majority of persons1 and in most of them is present all the time4 ,binocular fixation must be distinguished through three conditions--orthophoria1 heterophoria and squint4 ,,orthophoria ,this is the condition in which both eyes look straight at the same object1 whether both see it or not4 ,there is not the slightest tendency of deviation4 ,,heterophoria ,this is the condition in which both eyes keep looking straight at the same object so long as both see it2 but as soon as one eye is excluded from vision 7as by a screen7 that eye deviates4 ,this is then a tendency of deviation which is strong enough to become manifest when either eye is covered1 but which is abolished or overcome by the compelling impulse of binocular fixation as soon as both eyes are used for seeing4 ,a heterophoria thus produces a maximum deviation4 ,the deviation is also said to be latent1 since it is absent under ordinary conditions and is brought to light only under special conditions4 ,a common though improper term for heterophoria is 8insufficiency40 ,,squint ,squint is the condition in which there is so great a tendency to deviation that even when both eyes are uncovered1 one deviates and only one 8fixes40 ,it differs1 therefore1 from heterophoria in that the deviation it produces is obvious under ordinary conditions4 ,squint is also called strabismus1 or heterotropia4 ,in other words1 in orthophoria there is binocular fixation all the time and under all conditions2 in heterophoria it is present only when the two eyes are uncovered1 so that both see the object looked at2 while in squint it is not present at all4 ,or1 in still plainer terms1 in orthophoria both eyes are straight all the time2 in heterophoria both are straight1 but only so long as both are uncovered2 and in squint only one eye is straight1 no matter whether both eyes are uncovered or not4 ,in squint1 while binocular fixation is altogether absent1 the ability to perform monocular fixation is almost always preserved2 i4e41 the squinting eye will 8fix0 at once if the other eye is covered4 ,it is only when there is marked amblyopia1 particularly as the result of a central scotoma 7or spot on the cornea in the line of vision7 that the squinting eye loses its power to fix at all1 and wanders uncertainly about1 receiving impressions now on one1 now on another portion of the retina4 ,the term imbalance is often used to denote the two conditions opposed to orthophoria2 i4e41 to denote collectively heterophoria and squint4 ,,varieties ,,of ,,heterophoria ,,and ,,squint #a4 ,classification ,according to ,direction of ,deviating ,eye3 ,heterophoria and squint may be classified according to the direction assumed by the deviating eye4 ,thus we have the following varieties of heterophoria3 ,,heterophoria ,,lateral ,,deviations ,either eye deviates ,in1 or toward the nose ,esophoria ,out1 or toward the temple ,exophoria ,,vertical ,,deviations ,the right eye goes up and the left down ,right ,hyperphoria ,the left eye goes up and the right down ,left ,hyperphoria ,in rare cases of vertical heterophoria1 each eye has either an upward tendency 7anophoria7 or a downward tendency 7cataphoria74 ,these cases must not be confused with anatropia and catatropia4 ,in anaphoria and cataphoria1 there is binocular fixation when both eyes are uncovered1 while in anatropia and catatropia one of the eyes squints4 ,this shows the following squint condition3 ,,squint ,,lateral ,,squint ,the deviating eye turns in1 or toward the nose3 ,esotropia 7,strabismus convergens--,convergent ,squint7 ,the deviating eye turns out or toward the temple3 ,exotropia 7,strabismus divergens--,divergent ,squint7 ,,vertical ,,squint ,the deviating eye turns up3 ,hypertropia 7,strabismus sursumvergens7 7,right or left7 ,the deviating eye turns down3 ,hypotropia 7,strabismus deorsumvergens7 7,right or left7 ,in addition to these lateral and vertical deviations1 conditions exist in which the vertical meridian of one eye1 instead of maintaining its parallelism with the vertical meridian of the other1 either forms 7or tends to form7 an angle with it 7cyclotropia71 but is kept in position through muscular effort 7cyclophoria47 ,cyclotropia is usually due to paralysis of one of the ocular muscles1 causing the vertical meridian of the affected eye to be tilted out or toward the temple 7extorsion7 or in toward the nose 7intorsion74 ,a tilting of the vertical meridian toward the right is also called dextrotorsion 7or positive declination72 and to the left1 levotorsion or negative declination4 #b4 ,constant1 ,intermittent and ,periodic ,deviations3 ,a deviation1 whether squint or heterophoria1 may be present at all times 7constant71 or occasionally present and occasionally absent 7intermittent74 ,in this case we may have heterophoria alternating with orthophoria1 or heterophoria alternating with squint2 or squint alternating with orthophoria4 ,we also find variations such as a squint for near and a heterophoria or orthophoria for distance2 or a heterophoria for near and orthophoria for distance2 or a constant squint for near and an intermittent squint for distance1 etc4 ,again1 a deviation may be periodic1 in that its amount for distance may greatly exceed that for near1 or vice versa4 ,opposed to a periodic deviation is one which is present1 and in about equal amount1 both for distance and near4 ,such a deviation1 whether squint or heterophoria1 is called 8continuous40 #c4 ,alternating and ,uniocular ,squint3 ,an alternating squint is one in which when both eyes are uncovered1 so that both have a chance to 8fix02 sometimes the right eye will deviate1 sometimes the left4 ,in uniocular 7less properly monocular7 squint1 under the same conditions1 one eye1 either the right or the left1 always 8fixes0 and the other always deviates4 ,a uniocular squint is denoted as right or left1 according to whether it is the right or left eye which deviates4 ,illustration3 ,a ,,typical ,,refraction ,,room--,,the ,,woolf ,,sanitary ,,all-,,metal ,,equipment ,installation comprising3 ,ophthalmic ,chair1 complete with ,ski-optometer1 ,test ,letter ,cabinet1 ,asceptic ,trial-,case ,cabinet1 ,muscle ,testing and ,skioscopic ,lamp1 ,ophthalmometer1 ,perimeter1 ,adjustable ,tables1 ,adjustable ,stool4 #d4 ,comitant and ,non-,comitant ,deviations3 ,in some varieties of heterophoria and squint1 the amount of deviation is the same in all directions of the gaze1 so that the angle between the visual line of one eye and that of the other remains the same1 no matter which way the eyes are turned4 ,such deviations are called comitant or non-comitant1 because one eye accompanies and keeps pace with the other in all its movements4 ,in other cases1 the deviation changes as the eyes are moved in different directions1 so that the angle between the two visual lines constantly varies4 ,such deviations are termed concomitant4 ,usually in a non-comitant squint the angle of deviation increases in a regular way as the eyes are moved in one direction and decreases as they move in the direction opposite4 ,in cases of long standing1 however1 the squinting eye1 particularly when very amblyopic1 wanders in an uncertain way and apparently quite without reference to the movements of the other eye4 ,,chapter ,,xvi ,,law ,,of ,,projection ,the movements of the eye are designed primarily to effect fixation--that is1 to bring upon the macula the image of the object that we wish to look at4 ,when this has been accomplished1 we know as a result of long experience1 the direction of the object looked at and also direction of other neighboring objects4 ,this knowledge is doubtless afforded us1 in part1 by our muscle sense4 ,thus we know that an object1 ,a1 is straight in front of us because we can see it sharply without moving either the head or the eyes from the position of rest or equilibrium2 and we know that an object1 ,b1 is on the right of us because to see it sharply we have to move either the head or the eyes to the right1 thus altering the muscular condition from one of rest to one of tension4 ,but without moving either head or eye1 we also know1 while still looking at ,a1 that ,b is to the right1 for the image of ,b is then formed on a portion of the retina situated to the left of the macula4 ,from long experience we also know that an image so situated means an object placed on our right4 ,moreover1 the farther to the left of the macula the image ,b is1 the farther to the right do we judge ,b itself to be4 ,similarly1 if ,b is so placed that its image falls below the macula1 we then know ,b itself is really above ,a1 which forms its image on the macula2 and if the image of ,b is above the macula1 we know that ,b itself is below ,a4 ,the table on page #aaf is suggested as a guide in cases of muscular imbalance3 ,,suppression ,,of ,,image ,all deviations should be and probably are primarily associated with diplopia4 ,yet in the great majority of cases of established squint1 especially convergent squint1 there is no double vision4 ,this is due to the mental suppression of the image by the squinting eye4 ,in such cases all attempts to evoke diplopia by our tests may be futile1 the patient not appreciating the presence of double images even when they are widely separated by prisms4 ,moreover1 this suppression usually persists after the squint is cured1 so that even though there are two retinal images of the same object1 the mind perceives but one and ignores the other1 just as though it were not present4 ,in this case there is no true stereoscopic1 or solid1 vision4 ,,monocular ,,diplopia ,binocular diplopia1 due to deviation of the eyes or to prisms1 must be distinguished from monocular diplopia1 or the condition in which the patient sees double with one eye alone4 ,this occurs as the result of astigmatism1 plus spherical aberration and other conditions found occasionally in squint4 ,it can readily be differentiated by the fact that binocular diplopia disappears when the patient shuts either eye2 while monocular diplopia1 of course1 does not4 ,,table ,,of ,,diplopia ,image of right eye ,,caused ,,by as compared-------------------------------- ---- ,name of with that 7#b7 ,artificially diplopia of the 7#a7 ,by a natural by a prism left is deviation of placed1 base ---------------------------------------- ------------------------- ,homonymous ,on the ,either eye inward ,in before either right 7esophoria1 eye4 ,lat- esotropia47 eral ,heteronymous ,on the ,either eye outward ,out before either 7or crossed7 left 7exophoria1 eye4 exotropia47 ---------------------------------------- ------------------------- ,right ,below ,right eye up ,up before right or left eye down eye1 down before ,vert- 7right hyperphoria1 left eye4 ical right hypertropia1 left hypotropia47 ,left ,above ,right eye down ,down before right or left up eye1 up before 7left hyperphoria1 left left hypertropia1 right hypotropia47 ,image of right eye ,,corrected ,,by as compared-------------------------------- ---- ,name of with that diplopia of the 7#a7 ,turning 7#b7 ,prism placed left is with base ---------------------------------------- ------------------------- ,homonymous ,on the ,both eyes outward ,out before either right 7divergence47 eye4 ,lat- eral,heteronymous ,on the ,both eyes inward ,in before either 7or crossed7 left 7convergence47 eye4 ---------------------------------------- ------------------------- ,right ,below ,right eye down ,down before right ,vert- and left eye up eye or up before ical 7left left eye4 supravergence47 ,left ,above ,right eye up and ,up before right left eye down eye or down 7right before left4 supravergence47 ,,movement ,,of ,,each ,,eye ,,singly ,the movements of each eye individually are effected as follows3 ,the external rectus moves the eye directly outward2 the internal rectus1 directly inward4 ,the primary action of the superior rectus is to raise the eye4 ,because of the way in which the muscles run1 obliquely from within outward1 its lifting action increases when the eye is abducted and diminishes to little or nothing when the eye is adducted4 ,the inferior rectus carries the eye down4 ,owing to the oblique direction of the muscle1 its depressing action increases as the eye is abducted and decreases to zero as the eye is adducted4 ,the inferior oblique is inserted back of the equator of the eye4 ,hence it pulls the back part of the eye down and consequently throws the front part up4 ,it is thus an elevator of the eye1 reinforcing the action of the superior rectus4 ,owing to the way in which it runs1 from the front backward and outward1 its elevating action is greatest when the eye is adducted1 and diminishes to little or nothing when the eye is abducted4 ,the superior oblique1 so far as its action on the eyeball is concerned1 may be regarded as arising from the trochlea4 ,from this point it runs backward and outward and is inserted back of the equator of the eye4 ,it there pulls up the back part of the eye and consequently throws the front part down4 ,it is thus a depressor1 reinforcing the action of the inferior rectus4 ,owing to the oblique way in which it runs1 its depressing action is greatest when the eye is adducted1 and diminishes to little or nothing when the eye is abducted4 ,,subsidiary ,,actions ,besides these actions1 rightly regarded as the main action of the ocular muscles1 there are various subsidiary actions1 due to the oblique way in which the superior and inferior recti and the two obliques run4 ,thus1 both the superior and inferior recti adduct the eye1 their action being most pronounced when the eye is already adducted4 ,the two obliques1 on the other hand1 abduct the eye and do so most effectively when the eye is already abducted4 ,the superior rectus and superior oblique rotate the top of the vertical meridian of the eye inward 7intorsion72 while the inferior oblique and inferior rectus rotate it outward 7extorsion74 ,the superior and inferior recti act thus on the vertical meridian mainly when the eye is adducted2 the oblique1 on the other hand1 when the eye is abducted4 ,hence the eye is adducted by the internal rectus1 assisted toward the end of its course by the superior and inferior recti4 ,it is abducted by the external rectus1 assisted toward the end of its course by the two obliques4 ,it is carried straight up by the superior rectus and inferior oblique1 up and out by the superior rectus and external rectus 7the inferior oblique helping to carry it out1 but not up2 and in1 mainly by the inferior oblique and internal rectus74 ,the superior rectus assists in carrying it in1 but hardly up at all4 ,the eye is likewise carried straight down by the inferior rectus and the superior oblique2 down and out by the inferior and external recti1 and down and in by the superior oblique and internal recti4 ,,field ,,of ,,action ,,of ,,muscles ,as will be seen1 each muscle acts most energetically in some special direction of the gaze1 termed field of action of that particular muscle2 thus the external rectus acts most powerfully when the eye is directed outward1 and acts little or not at all when the eye is directed inward1 except by purely passive traction4 ,likewise the superior rectus acts mainly when the eye is directed down4 ,furthermore1 its action is limited to the upper and outer field2 for in the upper and inner field elevation is performed chiefly by the inferior oblique4 ,this is also true of all the other muscles4 ,,direction ,,of ,,the ,,gaze ,there are six cardinal directions of the gaze1 each corresponding to the field of action of one of the six ocular muscles as follows3 ,,cardinal ,,direction3 ,,muscles ,,specially ,,active3 ,straight out ,external rectus ,straight in ,internal rectus ,up and out ,superior rectus 7as an elevator7 ,up and in ,inferior oblique 7as an elevator7 ,down and out ,inferior rectus 7as a depressor7 ,down and in ,superior oblique 7as a depressor7 ,it is to be noted that the action of each muscle does not absolutely stop at the middle line1 but extends somewhat beyond it4 ,thus the action of the right externus extends not only throughout the whole right half of the field of vision1 but also some fifteen to twenty degrees to the left of the median line2 and that of the superior rectus extends not only above the horizontal plane but also somewhat below4 ,,primary ,,position--,,field ,,of ,,fixation ,under normal conditions1 when the head is erect and the eye is directed straight forward--that is1 when its line of sight is perpendicular to the line joining the centres of rotation of the two eyes in the horizontal plane--the muscles are all balanced4 ,this is called 8the position of equilibrium0 or the primary position4 ,it is this position which must be assumed by the patient in conducting tests for balance of the muscles4 ,from the primary position1 the eye may make excursions in every direction so that the patient can look at a whole series of objects in succession without moving the head4 ,this portion of space1 occupied by all the objects that may thus be seen directly by moving the eye without moving the head1 is called 8the field of fixation40 ,,binocular ,,movements ,while either eye alone may move in all possible directions1 one cannot move independently of the other eye4 ,under ordinary circumstances1 those movements only are possible which are regularly required to subserve binocular vision1 hence1 binocular single vision1 as well4 ,these movements are as follows3 ,,parallel ,,movements ,when one eye looks at a distant object the other is also directed to it1 so that the lines of sight of the two eyes are parallel2 if the distant object is moved about1 the lines remain parallel1 one moving as fast and as far as the other4 ,these parallel movements of the two eyes are executed with considerable freedom in all directions1 either eye being able to move readily to the right1 left1 up1 down1 or obliquely1 provided the other eye moves precisely with it4 ,in executing any parallel movement1 each eye is acted upon by at least three and sometimes by as many as five muscles4 ,at times1 but one of these muscles is required to produce any great movement of the eye1 the others simply serving to steady it in its course4 ,thus when we look up to the right1 although there are five muscles really acting upon each eye1 the right eye is moved mainly by the external rectus and the left eye by the internal rectus4 ,similarly1 when we look up and to the right1 although other muscles take part1 the superior rectus is the chief muscle that moves the right eye up1 and the external rectus the chief one that moves it to the right2 while for the left eye the inferior oblique and the internal rectus are the efficient muscles4 ,a careful study of the action of the individual muscles will make it clear that these facts hold good for each of the cardinal directions of the gaze4 ,furthermore1 if we attentively consider the action of the twelve muscles moving the two eyes1 we see that they may be divided into three groups1 viz42 four lateral rotators1 four elevators and four depressors4 ,,lateral ,,rotators ,right rotators ,left rotators ,l4 ,internal rectus to ,r4 ,internal rectus ,r4 ,external rectus ,l4 ,external rectus ,,elevators ,right-handed elevators ,left-handed elevators 7acting mainly when the 7acting mainly when the eyes are directed to the to eyes are directed to the right7 left7 ,r4 ,superior rectus ,r4 ,inferior oblique ,l4 ,inferior oblique ,l4 ,superior rectus ,,depressors ,right-handed depressors ,left-handed depressors 7acting mainly when the 7acting mainly when the eyes are directed to the eyes are directed to the right7 to left7 ,r4 ,inferior oblique ,r4 ,superior oblique ,l4 ,superior oblique ,l4 ,inferior rectus4 ,each group1 it will be seen1 comprises two pairs of muscles2 one pair acting solely when the eyes are directed to the right1 the other when they are directed to the left4 ,it will further be noted that of the two muscles constituting any one pair1 one is situated in the right eye1 the other in the left4 ,,eye ,,associates ,the muscles forming any one pair are called associates4 ,any two associates acting together will move their respective eyes in precisely the same direction and to the same extent4 ,thus the right superior rectus moves the eye up to the left and rotates its vertical meridian to the left2 and its associate1 the left inferior oblique1 moves its eye up to the left and rotates its vertical meridian to the left4 ,this likewise applies to each of the other five groups of associates4 ,if one eye fails to keep pace with the other in executing parallel movements1 diplopia ensues4 ,if the eyes are moved in all directions and the point noted where the patient just begins to see double1 we delimit the field of binocular single vision4 ,normally1 however1 the two eyes maintain parallelism to the very limit of their excursion1 so that diplopia occurs only at the extreme periphery of the field of vision1 if at all4 ,in fact1 the field of binocular single vision usually extends not less than #dj degrees from the primary position in every direction4 ,each of the various parallel movements of the eye appear to be governed by a distinct nerve mechanism1 there being one centre for movements to the right1 one for movements to the left1 one for movements up1 etc4 ,,movements ,,of ,,convergence ,in order to see an object at a nearby point1 the eyes have to converge--a movement affected by a simultaneous and equal contraction of both internal recti4 ,this movement may be combined with a vertical1 lateral or oblique parallel movement4 ,thus1 when we wish to look at a near object situated twenty degrees to our right1 we first turn both eyes twenty degrees to the right1 then converge both equally1 turning the left a little more to the right and the right a little back toward the left4 ,convergence is governed by a distinct mechanism of the nerves1 the source of which has not been determined4 ,,movements ,,of ,,divergence ,in passing from a position of convergence to a position of parallelism1 the lines of sight separate or diverge4 ,this movement of divergence is a simultaneous1 equal contraction of both externi2 or1 probably1 of both actions combined4 ,the eyes may even diverge somewhat beyond parallelism1 as in overcoming prisms1 base in1 when looking at a distant object4 ,,vertical ,,divergence ,the amount by which the lines of sight can separate in a vertical direction is very limited--at most but one or two degrees4 ,,orthophoria ,the term orthophoria is used to denote an absolutely normal balance of the extrinsic muscles1 just as the term emmetropia denotes a normal refractive condition4 ,they are equally rare4 ,,heterophoria ,the term heterophoria includes all those conditions in which there is a tendency to depart from normal balance1 but which nature is able to compensate for2 while the term also includes the conditions in which nature has been unequal to the task and an actual turning or squint has occurred4 ,,subdivisions ,the subdivisions of these terms at first reading appear complicated1 but prove simple enough on closer study1 indicating only the direction of the turning or tendency to turn4 ,for instance3 ,esophoria signifies inward tendency4 ,exophoria signifies outward tendency4 ,hyperphoria signifies upward tendency4 ,hypophoria signifies downward tendency4 ,cyclophoria signifies tendency to torsion4 ,esotropia signifies inward turning4 ,exotropia signifies outward turning4 ,hypertropia signifies upward turning4 ,hypotropia signifies downward turning4 ,cyclotropia signifies actual torsion4 ,combinations are describable in similar terms4 ,a tendency of the right eye to turn up and inward1 is a 8right hyperesophoria02 the left eye to turn down and out1 a 8left hyperexophoria10 etc4 ,tendencies of both eyes together are denoted by the terms which follow3 ,anaphoria signifies an upward tendency4 ,kataphoria signifies a downward tendency4 ,dextrophoria signifies a right tendency4 ,laevophoria signifies a left tendency4 ,,chapter ,,xvii ,,symptoms ,,of ,,heterophoria ,these depend on the kind of error present as well as the degree and widely vary4 ,in general1 they may be said to fall into three classes--7#a7 defective vision1 7#b7 pain of greater or less degree--7#c7 reflex symptoms4 ,defective ,vision4 ,the first class may be present1 even though each eye has a normal visual acuity2 since1 even when compensation is very good1 the brain gets the impression of two objects1 nearly1 though not quite fused2 and vision may be considerably worse with both eyes together than with either eye singly4 ,when compensation is considerably impaired1 the diplopia becomes more and more persistent1 till the brain finally makes choice of one image as more satisfactory1 entirely suppressing the other4 ,visual acuity may not suffer in either eye2 but vision being no longer binocular1 everything is seen in the flat1 the judgments of depth and distance being regularly more or less defective4 ,while this is a tremendous disadvantage in many occupations1 people gradually and not infrequently become accustomed to these visual defects and are not conscious of the handicap4 ,pain4 ,it is quite different with the second set of symptoms1 which are always accompanied with pain4 ,in fact1 the character of the subjective symptoms in refractive errors and muscular imbalance is so similar that it is practically impossible to differentiate in many cases4 ,in muscular asthenopia1 however1 in addition to becoming easily tired1 the patient often complains that letters seem to jump or run together or he may contend that he sees double for an instant2 or again that he can 8feel his eyes turn0 involuntarily in their sockets4 ,these pains or conditions are sometimes present only during actual use of the eyes4 ,at other times they persist for hours4 ,in some cases1 after days or weeks of overstimulation1 an explosion in migraine form occurs at irregular intervals4 ,this condition often lasts a day or two4 ,reflex ,symptoms4 ,in the third and last case1 there are other reflex symptoms--such as dizziness1 nausea1 fainting1 indigestion1 insomnia and pains in other portions of the body--sometimes stimulating organic diseases4 ,the possibility of heterophoria as a factor in chorea1 migraine1 neurasthenia and other diseases which may be primarily due to unstable nerves1 equilibrium is not to be forgotten4 ,it is a notable fact that when the fusion compensation fails so completely that one image is entirely suppressed1 or the diplopia is so great as to be overlooked1 the symptoms often cease entirely4 ,,treatment ,the treatment of heterophoria depends on a careful study of each individual case1 but it cannot be too strongly emphasized that in the great majority of cases the subjective symptoms disappear after a full correction of the refraction is made4 ,in many cases1 if the visual acuity in each eye be made normal1 the fusion impulse alone will be sufficient to restore compensation4 ,many cases of esophoria result from overstimulation of the centers for convergence and accommodation1 made necessary by hyperopia and astigmatism1 entirely disappearing when glasses abolish the need of accommodation4 ,cases of exophoria are sometimes due to the abnormal relaxation of accommodation and convergence which secures the best distant vision in myopia4 ,likewise the correction of myopia1 by increasing the far point1 may diminish the amount of convergence necessary for near vision4 ,prisms for constant use are often prescribed1 so placed as to help the weak muscles and counteract the strong4 ,for instance1 in esophoria we find the prism which1 base in1 will produce orthophoria for distance and prescribe a quarter of it1 base in1 before each eye4 ,while this is very successful in some cases1 the tendency in others is for the externus to increase slightly from constant exercise in overcoming the prism1 while the internus decreases in proportion to the amount of work of which it is relieved4 ,prisms for permanent use are very beneficial in vertical deviations1 since when the images are brought on the same level they require much less effort to secure fusion2 and when prescribed base up or down1 the effect secured is commonly an unchanging one4 ,we sometimes take advantage of this tendency when we prescribe for constant use weak prisms with the apex over the weak muscle1 which gradually becomes strong from the exercise of overcoming it4 ,this plan is effective only in patients who have a strong fusion impulse1 and the prism selected must be weak enough to be easily overcome4 ,we can accomplish the same effect by decentering the patient's refraction lenses4 ,for instance1 a convex lens so placed that the visual line passes the reverse will be the case if the lens is concave4 ,the amount of prismatic action depends on the strength of the lens and the amount of decentering1 the rule being that every centimeter of displacement causes as many prism diopters as there are diopters in that meridian of the lens4 ,thus #a sphere1 or cylinder axis #ij1 decentered one centimeter outward1 is equivalent to adding a one degree prism diopter lens1 base out4 ,,destrophoria ,,and ,,laevophoria ,these are terms denoting a condition in which both eyes are capable of abnormal rotating toward the right or left1 as the case may be4 ,the movement in the opposite direction is most common4 ,the patient can often rotate his eyes #fj degrees toward the right1 and to perhaps only #dj degrees to the left4 ,his position of rest is parallel with his visual lines1 but to the right1 in looking at objects directly in front1 he is much more comfortable with his head turned slightly to the left4 ,it is difficult to account for1 except on the theory that definite movement of the eyes is rather to the right than to the left in most occupations4 ,the position of the paper in writing at a desk tends toward dextrophoria2 in reading1 we move our eyes steadily from left to right and then begin a new line by a single brief movement to the left2 the things that a man uses most--whether he be laborer or student--are kept within reach of the right hand1 and in referring to them the eyes are constantly turned toward the right4 ,however1 when these conditions result from other imbalances1 they must be treated more carefully4 ,for instance1 a patient whose right internus is paralysed or congenitally defective on looking to the left1 has a cross diplopia which vanishes to the right2 as a result1 he soon assumes a habit of carrying his head in this position4 ,ordinarily1 this will cause no discomfort2 but if the left internus is so weak that it cannot follow the right externus to its position of greatest ease1 the visual lines are evidently different and the case must be treated as an exophoria4 ,if1 on the other hand1 the left internus over-balances the right externus1 the condition is an esophoria and must be treated as such4 ,similar reasoning applies to the conditions known as ,anaphoria and ,kataphoria1 in which the visual lines are parallel to each other but directed up or down with regard to the horizontal plane of the body4 ,in the first1 owing to congenital abnormalities1 the eyes usually tend upward and the individual must go about with his chin on his chest1 so that his eyes may look in front and yet remain in the position of rest4 ,in the second1 the chin is held in the air and the body arched backward4 ,but1 unless extreme1 neither of these conditions causes more than cosmetic difficulty and both should be undisturbed owing to the extreme difficulty of securing the same operative effect on both eyes4 ,suitable prisms are much more likely to be beneficial4 ,illustration3 ,supports for ,holding ,the ,ski-optometer ,floor ,stand ,illustration3 ,wall ,bracket ,illustration3 ,chair ,clamp ,illustration3 ,chair ,attachment with ,upright ,choice may be made from any of the above4 ,the ,wall ,bracket is recommended1 unless refractionist is provided with a specialist's chair1 to which the ,chair ,attachment with ,upright may be attached4