Chapter 17: Exodeviations

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Exodeviations 36742, 83, 117, 160intermittent deviations and anomalousretinal correspondence, 40 it has not been provedthat surgical results are functionally superior tothose in patients who have not received orthopticsor that surgery can be avoided2, 126, 173altogether by using this form of treatment. Flynnand coworkers 59 observed an improved sensorystate and better motor control in a group of patientswith intermittent exotropia who were treatedwith alternating occlusion. The dominant eye receivedocclusion more frequently than the nondominanteye (see also Knapp 99 and Iacobucciand Henderson 84 ). We have occasionally found itbeneficial to use alternating occlusion in lieu ofsurgery in patients with small angle intermittentexodeviations, as shown in Case 17–3.CASE 17–3A 5-year-old girl presented with a history of intermittentexotropia at distance fixation. Measurementsshowed orthotropia at near and an exophoria of 10 distance fixation. The distance deviation was easilydissociated and the patient did not spontaneouslyre-fuse. The patch test was negative. An insignificanthypermetropic refractive error was present.Stereopsis at near was 60 seconds of arc on theTitmus test and no stereopsis could be elicited atdistance with the Mentor B-VAT. In view of the smalldeviation at distance we decided against surgeryfor fear of causing an overcorrection. We orderedalternating occlusion instead and after 3 monthsthe patient fused at near and distance. She had anesophoria of 3 at near and distance. Stereopsis hadimproved to 15 seconds of arc at near and 60 secondsof arc at distance fixation. After 3 monthswithout treatment the findings were the same.Intensive orthoptic treatment may be indicatedpostoperatively when suppression persists or if aconvergence insufficiency type of exodeviation ispresent. Inagaki and coworkers 86 reported abolishmentof suppression and development of sensoryand motor fusion by treatment consisting of preoperativesimultaneous bifoveal stimulation with acheckerboard pattern in patients with constant andintermittent exotropia.Surgical TreatmentINDICATIONS FOR SURGERY. The need for surgeryis determined by the state of fusional control,the angle size of deviation, and the age of thepatient. In patients with manifest exotropia presentat or shortly after birth with no history of intermittency,surgery should be performed as soon asreliable and constant measurements can be obtained,the patient can alternate freely, and theangle of deviation measures at least 15 . We usuallyoperate on such children when they are between1 and 2 years of age. In adults with a largeangle constant exodeviation, surgery is performedas soon as the diagnosis has been established. Theprognosis for return of normal binocular functionin such cases is poor when the deviation hasbeen present since early childhood. Such patientsusually retain a residual small angle exotropiawith alternating fixation. However, exceptions tothis rule do occur, and we have seen several patientswho had a history of manifest exotropia formany years in whom unexpected and fortuitousreturn of normal binocular vision with stereopsisoccurred after surgical alignment of the eyes (seealso Ball and coworkers 9 ).Surgical treatment of intermittent exotropia orof constant exotropia preceded by a long periodof intermittency is directed at normalization ofbinocular function. There is good evidence for animprovement of distance stereoacuity aftersurgery. 144, 186 Unless there is definite evidence ofexisting defective binocular vision, surgery shouldbe preceded by several months of observationsince the disease does not progress in all patients 68,128, 135(see p. 359). Signs of progression includegradual loss of fusional control as evidenced byincreasing frequency of the manifest phase of thestrabismus. A patient whose eyes turn outwardonly occasionally and who is asymptomatic doesnot need surgery. However, when the exotropiaoccurs during more than 50% of waking hours orcauses asthenopic problems, surgery should beperformed. Other signs of progression are developmentof a secondary convergence insufficiency,an increase in size of the basic deviation, developmentof suppression as evidenced by absence ofdiplopia during the manifest phase of the strabismus,or decrease of stereoacuity. If one or severalof these signs or symptoms are present when thepatient is first examined or if they develop whilethe patient is under observation, surgery must beconsidered. An asthenopic patient with exophoriamay require surgery if the deviation cannot becontrolled with prisms.The most desirable age at which surgery shouldbe performed for intermittent exodeviations hasbeen a matter of some dispute. Jampolsky 90 prefersto delay surgery in visually immature infants to
368 Clinical Characteristics of Neuromuscular Anomalies of the Eyeavoid overcorrection. In the interval, he reinforcesfusion with minus lenses or prevents developmentof suppression by means of alternating occlusion.On the other hand, Knapp 98 is an advocate of earlysurgery for treatment of intermittent exotropia, aview shared by other authors. 3, 50, 146, 151, 156 Morerecently, however, Baker and coworkers 8 found ina comparative study that patients operated on afterthe age of 4 years had better functional results.We prefer to delay surgical intervention forintermittent exotropia in young children, since weshare Jampolsky’s concern about the effects of aconsecutive esotropia in a visually immature child.Unfortunately, in such patients, good preoperativevisual acuity in each eye with normal stereoacuitymay have been exchanged for persistent monocularesotropia with amblyopia, loss of stereopsis,and the development of anomalous retinal correspondence.Edelman and coworkers 52 reported that5 of 24 children who developed consecutive esotropiaafter surgery for exotropia before the ageof 4 years became amblyopic. Even when surgerywas delayed until the age of 4 to 6 years, amblyopiastill occurred in 3 of 39 patients.Although the prevalence of consecutive constantesotropia in patients under 5 years of agehas been reported to be only 10%, 96, 120, 151 we havewitnessed this unfortunate event in a sufficientnumber of our patients to advocate delaying surgeryuntil the child has reached at least 4 years ofage. In the interim, binocular vision should bereinforced with prisms base-in or minus lenses.Surgery at an earlier age should be consideredonly if there is a rapid functional deterioration offusional control in spite of nonsurgical therapy orif the deviation is constant.Finally, the size of the deviation determinesthe decision to operate. The angle of primaryexodeviations generally exceeds 20 , and unlikethe situation in esotropia, small angle exodeviationsare rare. If for functional reasons surgery isindicated, the deviation should measure at least15 at distance or near fixation before a procedureis carried out. Patients are seldom self-consciousor embarrassed by strabismus of this magnitudeand surgery usually is not performed unless thedeviation measures at least 20 to 25 .GOALS OF SURGERY. Although the aim of mostoperations for strabismus is to align the eyes asnearly as possible, many ophthalmologists haveproposed that for intermittent exodeviations asmall surgical overcorrection is desirable, since itappears that functional results will be more stable.Raab and12; 41; 53; 64; 81, p. 645; 90; 98; 152; 154; 164; 185Parks 152 proposed that the surgeon should strivefor an overcorrection of 10 to 20 . Lesser degreesof overcorrection have been associated with recurrenceof the exodeviations after some time haselapsed. A higher degree of overcorrection willnecessitate further surgery for consecutive esotropia.Proponents of deliberate overcorrection citethe therapeutic value of postoperative diplopia instimulating development of fusional vergences andthus in stabilizing eventual alignment of the eyes.On the other hand, it has also been shown that aninitial overcorrection does not guarantee a desirablefinal outcome. 159 Dunlap 51 observed that thedifficult element in striving for overcorrection isknowing how to produce some, but not too muchof it. In one series of his patients the prevalenceof unintended overcorrection was 40%, whereasCooper, 41 who deliberately attempted to overcorrecthis patients, reported a prevalence of only37%. Since introduction of adjustable sutures thisunpredictability has become less of a problem.We are in agreement with those who believethat a small angle of consecutive esotropia in theimmediate postoperative phase is desirable andtends to stabilize a functional result, even thoughsuch deviations occasionally may persist for along time and cause problems of management (seeCase 17–4). However, we have been unable toaccomplish this goal other than by pure chance orby postoperative suture adjustment.As pointed out above, surgical overcorrection,as beneficial as it may be in the older child oradult, must be avoided under all circumstances invisually immature children in view of the disastrousconsequences of a small angle esotropia inthis age group. On the other hand, Schlossmanand coworkers 162 concluded from their data thatadult patients do better with slight undercorrectionrather than overcorrection after surgery, providedthe residual exodeviation remains under 15 .Although it may be difficult or even impossibleto plan surgery to achieve a small, beneficialamount of overcorrection, there may be ways toavoid overcorrection in cases in which it is undesirable.The importance of including lateral gazeincomitance into the surgical planning has beenmentioned.CHOICE OF PROCEDURE. Burian 26, 31 emphasizedthat correct differentiation between the true andsimulated divergence excess patterns is essential
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Chapter 17: Exodeviations

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