Eye (1991) 5, 338-343

Strabismus in Children: The Prospects for Binocular Single Vision

H. E. WILLSHAW and J. KEENAN Birmingham

Summary The restoration or maintenance of useful binocular single vision (BSV) represents the ideal outcome in the management of a squinting child. However, in planning such management it is essential to have a clear appreciation of the likelihood of attaining that goal, and what factors will help in its attainment. Using both a literature review and some preliminary information from our own patient database we examine the prospects for BSV in different groups. We also discuss the techniques available to allow prediction of which children are candidates for the development of BSV following squint correction.

The ideal outcome in the management of a useful additional information. We also exam­ squinting child is the restoration or establish­ ine some of the ways in which the likelihood of ment of binocular single vision (BSV) and developing BSV may be predicted in any indi­ motor fusion. With these goals secured the vidual child. strabismus surgeon can look forward to the long-term stability of the surgical result. If these objectives cannot be achieved then the (a) Congenital! Early Infantile natural progression towards divergence with An extensive literature on this group of increasing agel will tend to give rise to increas­ patients has flourished, largely because it ing numbers of cosmetically unsatisfactory represents a discrete, easily identifiedcohort. results and to late surgical correction of con­ The major discussion centres on the timing of secutive with the attendant risk of surgical intervention, the prospects for BSV intractable . and the quality of BSV obtained.2.3.4.5 When Our surgical objectives, be they orthopho­ evaluating such reports care must be exer­ ria, deliberate undercorrection or deliberate cised in assessing the different results overcorrection should, therefore, be guided reported using different tests of BSV. Particu­ by the expectation of useful BSV resulting larly, as Harcourt and Mein point out, the from treatment. This review examines some presence of motor fusion in the early post­ of the theoretical considerations reiating to operative period does not necessarily corre­ different types of straol'2>ffius, ano. sup­ late with stable BSV later.6 Nonetheless, it plements those considerations with infor­ does appear that a significant proportion of mation obtained from interrogation of our such children will develop microtropia with own patient database. The database consists if corrected to within 10 prism of consecutive patients followed for at least dioptres by two years of age/ and that this fiveyears, and while currently small, provides outcome greatly reduces the risk of consec-

Correspondence to: Mr H. E. Willshaw, Department of Paediatric Ophthalmology, Birmingham Children'S Hospital. STRABISMUS SURGERY IN CHILDREN 339 utive exotropia. 8 Since there is no pressing or anisometropia achieved BSV anaesthetic argument for delaying strabismus (emphasising the need for active amblyopia surgery beyond this age, it has been our policy therapy prior to surgical correction). For since 1982 to perform the initial surgery for those children satisfactorily aligned by 18 to early onset esotropia at 14 to 18 months of 24 months, we find 31 % achieve stable BSV. age, so that further procedures (necessary in Interestingly, unlike previous authors,S we 33% to 45% of children9•1O) can be completed have found the presence of dissociated ver­ before the second birthday. As well as afford­ tical deviation (DVD) before the age of 2 ing an opportunity for the development of years to be incompatible with the develop­ BSV, early surgery may also improve the ment of worthwhile BSV. general performance of the child, an obser­ vation often made by , and recently (B) Accommodative Esotropia quantified.I! Fully accommodative esotropia should not be Amongst a group of patients with esotropia considered in this discussion since surgery is present before six months of age, will be other not indicated, and full refractive correction is entities masquerading as congenital esotro­ the treatment of choice. The parents' com­ pia. Duane's Retraction syndrome, bilateral monly expressed worry about long-term spec­ sixth nerve palsies and the block­ tacle wear can to some extent be alleviated by ing syndrome are identified at the initial pointing out the good results possible with assessment. The child with early onset accom­ contact correction as an alternative. 16 modative esotropial2 must also be identified (to avoid inappropriate surgery) and any (C) High AC: A Ratio Esotropia hypermetropic correction of +2.00 dioptres From a practical point of view, this can be con­ or more should be given to assess its effect. 13 sidered to exist whenever the near deviation Similarly, the neurologically damaged child exceeds the distance deviation by 10 prism with early onset esotropia needs to be recog­ dioptres or more. !7 There may be no deviation nised, since the behaviour of the squint may in the distance, or alternatively an esotropia be quite different14 and because the prospects for distance which increases with accommo­ for useful BSV are so much poorer!) that dation. Control of the near deviation can be delaying surgery to allow complete stability of achieved in several ways. In the United King­ the deviation is justifiable. dom there is a reluctance to use bifocal spec­ Results from our database on this group of tacles as the mainstay of treatment, since it is children are shown in Table I. Only one child perceived that the child may become depend­ operated on after the age of two years devel­ ent on the spectacles to avoid asthenopic oped . BSV, and no child with persistent symptoms in later life. 18 Bifocals may, how-

Table I Preliminary database-all patients followedfive years or more

Type of Pre-op Age@ % BSV Deviation Amblyopia Surgery % BSV @5 Years N

True Dist. 0 77 mths 81. 8% 72. 7% 11 Exotropia (36-142) Sim. Dist. 81 100% 100% 6 Exotropia (62-162) Other Types 3 92 45. 4% 45. 4% 11 Exotropia (50-163) Congenital 8 33 19. 2% 19. 2% 26 Esotropia (9-88) High AC: A 0 52 80% 80% 5 Esotropia (32-73) Non Accomm. 4 71 47% 47% 17 Esotropia (29-135) Other Types 4 62 37. 5% 37. 5% 8 Esotropia (21-108) 340 H. E. WILLSHAW AND 1. KEENAN ever, be employed in a more limited way using dioptres or more, whilst most of those failing them for a trial period to determine whether to achieve BSV had larger residual angles. It good quality BSV is established when the may be that more aggressive surgical correc­ deviation is fully corrected. If this proves to be tion with the likelihood of a higher incidence the case, the bifocal segment can then be of consecutive exotropia (rather than seeking gradually reduced, and surgery undertaken if a deliberate undercorrection in such cases) the quality of BSV falls. To limit the cost of might lead to an increase in the functional this approach, fresnel spherical lenses may be cure rate. used, but whatever the form of the bifocal, it One finalcomment on esotropia correction must be sufficiently high to ensure use of the (which might equally well apply to other types bifocal segment in near viewing. In practice of strabismus) relates to surgical planning this means the use of an "executive" style where the anticipated outcome is BSV. In bifocal with the upper border situated at the such cases all barriers to fusion must be dealt lower pupillary border. with, and this particularly applies to disorders Pharmacological manipulation of accom­ of the cyclovertically acting muscles. Since we modation can be used in the same way. Since are incapable of generating motor torsional the withdrawal of Phospholine Iodide19 this fusion,z2 and have a limited range of vertical involves the use of another parasympathomi­ fusion, both these elements should be taken metic agent, usually Pilocarpine. Parasympa­ into consideration at the time of surgery, the thomimetic agents can also be used as an torsional component will usually be dealt with indicator of BSV potential rather than in a by surgery to the obliques, whilst the vertical truly therapeutic way. As with bifocals a component can be predictably remedied using gradual withdrawal of Pilocarpine over sev­ a transposition procedure at the time of hori­ eral weeks will occasionally reveal a cure, but zontal rectus surgery. 23 more commonly indicates the functional potential in a particular patient. Exotropia Adopting an approach in which surgery fol­ (a) True and Simulated Distance Exotropia lows initial identification of BSV potential Though quite distinct entities, these two are would be anticipated to provide a high yield of grouped together because of the excellent long-term BSV results, and this is borne out in functional cure rates to be anticipated in each. Table I. Four of five patients in this category Because these children are straight for near have good quality BSV at five-yearfollow-up. (even if controlling an exophoria) they retain The ideal surgical alignment in such children good binocular co-operation until late in the is probably orthophoria, though, for the more natural history of their deviation. For this courageous, there is evidence that a small reason, well timed surgical intervention will overcorrection (less than 10 prism dioptres) usually re-establish stable BSV. yields a significantly higher proportion of There are conflicting recommendations in functional cures in acquired .2o,21 the literature. Several authors have docu­ mented the increased long-term stability .of (D) Partially Accommodative and Non the surgical results (as gauged by the need for Accommodative Esotropia reoperation) when initial surgery is per­ Unfortunately, the major group of esotropes formed after the age of four years.24,25 Con­ any of us will encounter falls into these two versely, Pratt-Johnson et al advocate early categories. It may be that many began as surgery and document a higher functional accommodative deviations but by remaining cure rate with early surgery.26 Our approach uncorrected for some time developed secon­ has been to use minus lenses to maintain con­ dary features which were not correctable by trol of the deviation to the age of four if pass­ removal of the accommodative component. ible27 (while prisms could be used in the same In our group of children, however, almost half way,28 they appear to be rather less effective) were still able to achieve BSV following sur­ and then proceed to surgery where necessary. gical correction. Only one child achieving With this approach, 15 of 17 children followed BSV had a residual deviation of 10 prism for fiveyears or more show maintained BSV, STRABlSMUS SURGERY IN CHlLDREN 341 though in seven of the children there has been because of this, we have been cautious in an increasing exophoria over that period and interpreting this particular test and, if it is the one wonders whether longer review might only indication of BSV, have tended to adopt show some loss of control. This regime is by a conservative approach to surgery (i.e. delib­ no means sacrosanct, and the single departure erate small under correction in the case of eso­ from it in this group also showed an excellent tropia). The other sensory tests are much result. more dissociating, particularly if performed Such a high yield of BSV is not seen in other through prisms, but if positive provide categories of divergence (Table I). Approxi­ unequivocal proof of BSV potential. The mately half the children with a basic exotropia prism adaptation test described by Jampol­ developed BSV (only one of whom was oper­ skl9 overcomes the problems of interpreta­ ated on before the age of four) but no child tion inherent in the sensory tests since it with consecutive exotropia had BSV estab­ provides an easily interpreted motor lished by its correction. response. Unfortunately to get a definitive These results in the common forms of hori­ result may take several weeks, with manipu­ zontal strabismus are encouraging, and sug­ lation of the prisms, and this has deterred gest that the widely applied guidelines of many from employing it on a regular basis. management are realistic and appropriate. In In the search for a single test which can be particular, with aggressive amblyopia therapy performed at the time of preoperative assess­ followed by accurate and well timed ocular ment and which is applicable to the very alignment, we can anticipate a functional out­ young child with congenital esotropia, a come in the majority of exotropes and a vary­ number of researchers have turned to elec­ ing number of esotropes, depending on the· trophysiological techniques. type of strabismus. Since 1978 it has been recognised that the However, the empiric data referred to so binocular visually evoked potential (VEP) far only tells us the probability of a BSV result may be greater than the sum of the monocular in a series of children, but takes us no closer to VEPs/o and that this summation is absent in predicting the outcome in an individual child. patients with suppression3! or in subjects with To do this, it is necessary to interpret infor­ normal BSV which has been disrupted using a mation from a variety of techniques used to vertical prism.32 However, it has been argued identify the child with BSV potential. They that this apparent summation may represent can be divided into established tests with the excitation of two independent pools of which all ophthalmologists and their orthop­ monocularly driven neurones rather than tists will be familiar, and less well established recruitment of binocular cortical neurones.33 techniques designed to address the particular For this reason other investigators have used problems found in the uncooperative and pre­ random dot stimulii. verbal child. Table II Te sts of pote ntial binocular single vision Table II indicates some of the tests which

can be used to predict the likelihood of a func­ 1. Standard Tests used with or without prismatic tional outcome following strabismus surgery. correction In the presence of a manifest deviation a posi­ Lang 2 Pen tive response to these tests suggests the pres­ Bagolini Lenses Worth 4 Dot ence of anomalous retinal correspondence Stereograms (ARC) which may be modifiedfollowing sur­ Synoptophore gery and which represents an encouraging situation. 11 The least dissociating of the tests is 2. Tests of Motor Response 15 Dioptre prism test the Lang 2 pen test which is most useful in Prism adaptation test older patients, but may be difficult to inter­ pret in a less co-operative younger child. The 3. Electrodiagnostic Tests Bagolini lenses unfortunately produced in our Summated visually evoked potential experience a BSV response when all other Dynamic Random Dot corrclogram Dynamic Random element stereogram tests suggest the presence of suppression, and 342 H. E. WILLSHAW AND J. KEENAN

Two main approaches have been employed: characteristics and course of early infantile eso­ tropia. J Pae d Ophthalmol and Strab 1988 24: The dynamic random dot stereogram, in 276-81. which a stereogram composed of red and 10 Ing MR: Early surgical alignment for congenital eso­ green dots is generated and can be moved tropia. J Pae d Ophthalmol and Strab 1983 20: 11-18. around the screen. The child's eye move­ 11 ments are then recorded and correlated to the Rogers GL, Chazan S, Fellows R, Tsou BH: Strabis­ movement of the stereogram.34 Studies with mus surgery and its effect upon develop­ ment in infantile esotropia. Ophthalmology 1982 such a system have showed the early develop­ 89: 479-82. 1 ment of BSV, and also the restoration of BSV 2 Baker JD and Parks MM: Early onset accommo­ following early surgery for congenital dative esotropia. Am J Ophthalmol 1980 90: esotropia.35 11-18. 13 Burian HM and Von Noorden GK: In Binocular A second approach has been to use the vision and ocular motility, e. v. Mosby Co. 1980, dynamic random dot correlogram which is P 297. 14 easier to generate and less sensitive to head Buckley E and Seabcr JH: Dyskinetic strabismus as movements. The Cambridge group demon­ a sign of ccrcbral palsy. AmJ Ophthalmol198191: 652-7. strated its value in 198036 and more recently, 15 Holman RE and Merritt JC: Infantile esotropia: Rossiter in Birmingham has used a modified Results in the neurologic impaired and 'Normal' technique to assess binocular function.37 child at NCMH (six years) J Pae d Ophthalmol and To the best of our knowledge, neither of Strab 198623: 41-4. these approaches has been applied to a large 16 Calcutt C: The use of contact lenses in the treatment of accommodative esotropia. Trans Fifth Tnt clinical group, and it may well be that the time Orthop Congre ss1984, 311-15. 1 is right to undertake such a study. 7 Parks MM: Ocular Motility and strabismus 1975, Harper & Row, Hagerstown, Maryland. There is at the moment, no test which can 18 be relied upon accurately to identify all Mein J and Harcourt B: In Diagnosis and Manage­ ment of ocular motility disorders, Blackwell squinting children who have the potential to Scientific Publications 1986b, 199. 1 develop BSV. The traditional sensory tests 9 Goldstein JH: The role of miotics in strabismus, are most useful but almost certainly provide Surv Ophthalmol1968 13: 31-46. 0 an underestimate because of the dissociation 2 Windsor CE: Surgically overcorrected esotropia: A study of its cause, sensory anomalies, fusional involved in their performance. A reliable and results and management. Am Orthop J 1968 16: easily performed electro diagnostic assess­ 8-15. ment would be a useful addition to the tech­ 21 Dankner SR, Mash J, Jampolsky A: Intentional sur­ niques available. gical overcorrection of acquired esotropia. Arch Ophthalmol1978 96: 1848-52. References 22 Ruttum M and Von Noorden GK: Adaptation to tilt­ 1 Burian HM: Hypermetropia and esotropia. J Pae d ing of the visual environment in cyclotropia Am J Ophthalmol1971 9: 135-9. Ophthalmol1983 96: 229-37. 2 Costenbader FD: Factors in the cure of squint in 23 Willshaw HE and O'Connor GM: Transposition sur­ Strabismus Ophthal Symposium (1950), St Louis, ge ry in childhood strabismus. Eye 19882: 41-3. e. v. Mosby Co. 24 Jampolsky A: Treatment of exodeviations in Pae­ 3 Riise P: Results in in early operation diatric Ophthalmology & Strabismus Trans. Ne w in esotropia. Acta Ophthalmol1953 31: 117-22. Orle ans Acade my Ophthalmol. 1986, p 201-34, 4 Taylor DM: Congenital strabismus: The common C. V. Mosby. sense approach. Arch Ophthalmol 1967 77: 25 Hardesty HH, Boynton JR, Keenan PJ: Treatment 478-84. of intermittent exotropia. Arch Ophthalmol1978, 5 Hiles DA, Watson BA, Biglan AW: Characteristics 96: 268-74. of infantile esotropia following early bimedial rec­ 26 Pratt-Johnson JA, Barlow JM, Tillson G: Early sur­ tus recession. ArchOphthalmol1980 98: 697-703. gery in intermittent exotropia. Am J Ophthal­ 6 Mein J and Harcourt B: In Diagnosis and manage­ mology 1977, 8 4: 689-94. ment of ocular motility disorders, Blackwell 27 Caltrider N and Jampolsky A: Overcoming minus Scientific Publications (1986a): 234. lens therapy for the treatment of intermittent exo­ 7 Ing M, Costenbader F, Parks MM: Early surgery for tropia. Ophthalmology 1983,90: 1160-5. congenital esotropia, AmJ Ophthalmol1966 61: 28 Hardesty HH: Prisms in the management of inter­ 1419-27. mittent exotropia. Am Orthop J 1972, 22: 22-30. 8 Vasquez R, Calhoun JH, Harley RD: Development 29 Jampolsky A: A simplified approach to strabismus of in congenital esotro­ diagnosis. Symposium on Strab. Trans. New pia. J Pae d Ophthalmol and Strab1981 18: 42-4. Orleans Academy Ophthal 1971 p 66-75, Mosby, 9 Robb RM and Rodier DW: The variable clinical St Louis. STRABISMUS SURGERY IN CHILDREN 343

30 Srebro R: The visually evoked response: Binocular 34 Fox R, Aslin RN, Shea SL, Dumais ST: Stereopsis in facilitation and failure when binocular vision is human . Science Reprint Series 1980, 207: disturbed. Arch Ophthalmol 1978, 96: 839-44. 323-324. 31 Campos EC and Chiesi C: Binocularity assessed 35 Archer SM, Helveston EM, Miller KK, Ellis FD: with visually evoked responses. Trans Fifth Int. Stereopsis in normal infants and infants with con­ Orthoptic Congress 1983, 415-20. genital esotropia. Am J Ophthal 1986, 101: 32 Campos EC and Chiesi C: Binocularity in comitant 591-596. strabismus: 11 Objective evaluation with visual 36 Braddick 0, Atkinson J, Juless B, Kropfe W, et al: evoked responses. Documenta Opthalmologica Cortical binocularity in infants. Nature 1980, 288: 1983,55:277-293. 363-365. 33 Shea SL, Aslin RN, McCulloch D: Binocular YEP 37 Rossiter LI: An evaluation of binocular visually evo­ summation in infants and adults with abnormal ked responses recorded to a dynamic random dot binocular histories. InvestOph & Vis Sci 1987, 28: corelogram in normal BSV and comitant unilat­ 356-365. eral BSc thesis submission.