Arch Dis Child: first published as 10.1136/adc.64.3.413 on 1 March 1989. Downloaded from

Archives of Disease in Childhood, 1989, 64, 413-418

Personal practice The management of squint

A R FIELDER Department of , University of Leicester Medical School, Leicester

Squint may be the first sign of a serious ocular or early neonatal life about 32% of infants are diver- systemic disorder, and yet it is also one of the most gent and only 3% convergent.4 As the incidence of common ocular conditions of childhood. It follows divergence is higher in preterm neonates it is likely that while most ocular deviations have no such that during development the are initially sinister connotations, an understanding of the range divergent but that this resolves over the first few of associations is essential to be prepared for this weeks of life. comparatively infrequent but important possibility. Apart from those seen in the neonatal period, Screening for squint has been covered recently' squints are comparatively uncommon in the first few and in this article its presence will be assumed. The months of life, and the term 'infantile' is preferred clinical evaluation of the child with a squint will be to 'congenital' because this type of is considered first, followed by a discussion of the aims rarely if ever congenital but develops between 3 and and methods of treatment. The main thrust will be 6 months of age. Characteristically the deviation is directed towards the squint itself, but as large, constant, and there is no appreciable refrac- is such a frequent and important association this tive error.5 topic will also be covered briefly. In order to avoid Apart from the infantile type, the onset of extensive and tedious repetition the associations of esotropia in childhood is most common between 11/2 squint will be listed using a predominantly system and 3 years of age. The deviation may range from based approach. Subdivision into paralytic and non- the hardly detectable (microtropia) to the cosmeti- paralytic types is only done at a later stage as both cally obvious manifest squint, and may be intermit- http://adc.bmj.com/ may occur in certain categories. Inevitably this tent or constant. In some the deviation increases- classification has limitations and inaccuracies, but or is only present-on (partially hopefully it will help the paediatrician to consider and fully accommodative squints respectively). the possible implications of a squint. For further Many, but by no means all, are associated with reference the reader may wish to consult two refractive errors. excellent standard texts.2 3 is less common than esotropia at all ages and has less propensity to cause amblyopia. In Squint and its associations infancy ocular divergence should alert the clinician on October 1, 2021 by guest. Protected copyright. to the possibility of a severe . SQUINT AS AN ISOLATED ANOMALY Paralytic squints do occur as an isolated anomaly Recently emphasis has been placed on early referral in an otherwise healthy child, but a careful search of infants and children with squint, but this has not for an underlying cause must always be undertaken taken into account that during the neonatal period (see acute central nervous system disease). Most, such a deviation may be a normal event. During but not all, paralytic squints in children are con- genital rather than acquired, although the role of birth trauma as a causal factor has probably been greatly overemphasised. A sixth cranial nerve palsy In terms will be used this article the following may present at this interchangeably: squint and , esotropia birth but characteristically and convergent squint, exotropia and divergent resolves over the ensuing few weeks. Apart from squint, comitant and non-paralytic squint, and this clinically obvious and rare exception, the most incominant and paralytic squint. Comitance will be common palsy, of the fourth nerve, is usually not assumed unless the terms incominant or paralytic diagnosed for a year or so as the ocular deviation is are used. difficult to elicit in infancy and the presenting sign is usually a compensatory head posture. Third nerve 413 Arch Dis Child: first published as 10.1136/adc.64.3.413 on 1 March 1989. Downloaded from

414 Fielder palsy is less common but more obvious, and in may be unilateral, bilateral, and concomitant or children is more likely to be congenital than acquired. paralytic, or both. Causes include raised intracranial A form of the latter that usually commences in pressure, intracranial tumours, trauma, degenera- childhood is ophthalmoplegic migraine. Benign tive and inflammatory diseases.6 12 recurrent , thought to be a post- infective mononeuropathy as it usually follows a Neurodevelopmental disorders-In general, the inci- febrile illness, is included here because at presenta- dence of ocular abnormalities in children with tion there are no associated systemic or neurological neurodevelopmental disorders including Down's signs.6 In the superior oblique tendon sheath syn- syndrome and cerebral palsy ranges from about 40% drome (Brown's syndrome) elevation of the in to 90%.12 Of these squint is the most common with adduction is limited. The aetiology of this condition an average incidence of about 40%,12 15 depending may differ between cases from a congenital anomaly both on patient selection and the nature of the of the tendon sheath to an acquired swelling of the neurodevelopmental disorder. Although both comi- tendon. tant and incomitant deviations occur the former are far more common. SQUINT AND OCULAR DISEASE Squint may be the presenting sign of serious ocular Brain stem dysfunction-Two conditions need to be disease. The eyes of a blind infant are commonly, considered in this category: Duane's and Mobius' but not invariably, divergent. Most important, syndromes. Duane's syndrome is relatively common squint either convergent or divergent may be the and superficially resembles a sixth nerve palsy and first sign of a treatable and potentially life threaten- its identification can obviate the need for extensive ing condition such as retinoblastoma. Thus squint investigation Often an isolated anomaly, it can be can be associated with unilateral or bilateral ocular associated with other congenital abnormalities such disease, including and retinal disorders such as Goldenhar's syndrome, spina bifida, and deafness. as regressed of prematurity (see below). Mobius' syndrome is either a developmental defect Esotropia also develops in some children with or an acquired hypoxic insult to the cranial nerve congenital . nuclei and is characterised by bilateral facial weak- ness, horizontal gaze palsies, and esotropia in some SQUINT AND SYSTEMIC CONDITIONS cases. Affected children are usually mentally re- Many systemic conditions can be associated with tarded, deaf, and exhibit limb malformations. strabismus and it would not be sensible or indeed possible to list them all here. Instead only a few will Muscle disease http://adc.bmj.com/ be considered and these will be grouped into broad Uncommon in routine clinical practice and can categories. easily therefore be misdiagnosed. Extraocular muscle involvement in myasthenia usually involves Prematurity the levator muscle of the resulting in The incidence of comitant squint is increased in and may also affect any other extraocular muscle infants born prematurely with figures quoted from leading to . Characteristically myasthenic -9 with and the can be 11% to 19%. The pathogenesis of this association symptoms increase fatigue signs on October 1, 2021 by guest. Protected copyright. is not well understood but is almost certainly due in unilateral or bilateral. Ocular motility hIay be part to both the perinatal neurological insults and affected in other muscle disorders and esotropia retinopathy of prematurity to which these infants may occur in myotonia congenita. Ophthalmoplegia are susceptible. A high incidence of squint has also is seen in a number of muscle disorders including been reported in term and preterm infants who congenital and other myopathies, dystrophia myo- have had phototherapy for the treatment of tonia and mitochondrial cytopathy. As in these last hyperbilirubinaemia,l° but a causal relationship mentioned conditions the limitation of ocular move- between these two and squint has not been defined ments is usually symmetrical, diplopia is not a particularly as many of these babies will also have common symptom. Rarely only the extraocular suffered the aforementioned complications. muscles are involved as in the congenital fibrosis syndrome. Disorders of the central nervous system Acute diseases of the central nervous system-The ORBITAL CONDITIONS association between squint and acute serious disease In this group of conditions certain ocular move- of the central nervous system is well known, and it ments are limited, due not to a neurogenic cause, must always be remembered that it may be the first but to mechanical restriction of the muscle move- sign of serious neurological disease. The deviation ment. Examples include injury such as orbital blow Arch Dis Child: first published as 10.1136/adc.64.3.413 on 1 March 1989. Downloaded from

The management of squint 415 out fractures and infections. Squint may be the first caution as children can confuse physiological and sign of an orbital tumour such as rhabdomyosarcoma. pathological diplopia. The term diplopia is also sometimes used to describe blurred vision, as in the Investigation uncorrected myope. As children relatively rarely complain of diplopia, indirect evidence such as Even now the evaluation of a squint, and its. effect closing one eye when looking in a particular on the , remains essentially clinical. direction can be helpful. Often there is a disparity The obvious priority is to identify first those con- between history and findings concerning the follow- ditions that require urgent treatment, and inves- ing signs: squint, ptosis, compensatory head pos- tigation should consequently be directed initially ture, proptosis, and inequality. In this situation towards three aspects. First the type of squint, a selection of photographs can be invaluable in whether it is paralytic or non-paralytic, and either distinguishing old from fresh pathology and obviate congenital or acquired; second, the identification of the need for extensive investigations. amblyopia; and third, the presence of associated pathology in the eye, , or elsewhere. The extent General history of this spectrum has already been indicated and Information on pregnancy, perinatal history, and clearly the prevailing clinical conditions in an general development are obviously important, but individual patient will dictate the relevance of each for the readers of this article need not be stressed. of these topics. Nevertheless as squint may be the first sign of a serious neurological or ocular abnormality, the DETERMINING THE TYPE OF SQUINT history must take these possibilities into account. Differentiating the paralytic and non-paralytic squint is important and sometimes difficult. Exem- EXAMINATION plified by sudden onset squint a relatively common Ophthalmic examination clinical dilemma in which determining the type (or Measurement of visual acuity is the first step, but even types) of squint is often difficult and can be at this remains the Achilles heel of paediatric ophthal- times impossible, particularly in the young fractious mology. Even at the age of 31/2 years accurate child. 16 A sudden onset is suggestive, but not measurement is often not possible using standard pathognomonic, of paralysis and can also occur with tests.17 Preferential looking based techniques are non-paralytic deviations, and on occasion both types opening important new horizons in clinical vision may coexist. assessment, but as yet caution must be expressed It is pertinent to review the natural history of regarding their accuracy in amblyopia measurement http://adc.bmj.com/ paralytic strabismus, which at its onset is characte- in the very young.18 Therefore in this population, rised by a deviation greatest in the direction of evaluation remains qualitative, relying on such action of the paretic muscle. Over the ensuing observations as objection to the occlusion of one weeks and months there is tendency for 'spread of eye. comitance' to occur, with the deviation spreading to Look for any facial, orbital, eyelid, or ocular all positions of gaze, so that eventually it becomes asymmetry. Surprisingly when this is present deter- indistinguishable from a comitant squint and the mining which side is abnormal may not be simple. paretic muscle cannot be identified. The following Thus a mother's comment that the right eye is on October 1, 2021 by guest. Protected copyright. points may help in distinguishing a recent from an smaller could denote just that. It could also indicate old paresis, or comitant squint. Diplopia is a feature the presence of a right ptosis, right , of a recent paresis but not ofother types. Amblyopia is or left proptosis, all of which could, by different present in longstanding but not recent deviations mechanisms, be associated with strabismus. and past pointing is a feature only of the latter. A Assessment of the squint and ocular motility, compensatory head posture is often present in both including the cover test, is mandatory. Ocular new and old pareses, but rarely in a primary movements must be tested in all positions of gaze, comitant squint, and the former two can readily be and while many paretic squints are obvious, during differentiated by scrutinising old photographs. the recovery phase limitation of movement may be almost undetectable. In this instance further tests HISTORY (for example, Hess chart) of overaction of the Ocular history synergistic muscle of the other eye can be invaluable. Diplopia indicates a recent onset deviation, usually No ophthalmic examination is complete without paretic. If spontaneously volunteered by the patient assessment of the pupillary reactions, visual fields it can usually be relied upon, but this symptom (when indicated) and fundoscopy. As many squints extracted by direct questioning must be treated with are associated with an abnormal refractive status, Arch Dis Child: first published as 10.1136/adc.64.3.413 on 1 March 1989. Downloaded from

416 Fielder except where urgent clinical problems preclude, methods equally effective, although there was no mydriatic refraction is an essential part of the improvement in 23% .19 If no improvement was assessment. achieved with one method it was worth trying one of the alternatives.'9 If the amblyopia is refractory to Systemic examination treatment, as a last resort a short period of intensive Most squints occur as an isolated anomaly; however, occlusion on an inpatient basis may be undertaken. the possibility of coexistent or causal systemic Occlusion is continued until either the visual acuity pathology must not be forgotten, and a detailed is restored to normal, or failing this, remains stable paediatric assessment undertaken if indicated. for at least three months. After cessation of treat- ment vision may deteriorate again in about 50% of ADDITIONAL INVESTIGATIONS cases,20 and further periods of occlusion may be Having already indicated the range of conditions required. If amblyopia is to recur this usually occurs that can be associated with strabismus, the need for soon after the completion of treatment, but can be additional tests such as a Hess chart, tensilon test, much later at about 12 to 13 years of age. Compliance muscle biopsy, or computed tomogram is dictated is a common problem not surprising as occlusion is by the prevailing clinical conditions and will not be unpleasant particularly when the amblXopia is considered here. dense. Reported success rates vary: 77%,' 92%,21 or 100%.2 Flynn and Cassady reported success in Treatment only 56%, but their series included patients with form deprivation amblyopia, a particularly difficult The aim of treatment is to restore binocular single group to treat.22 Despite these varying success rates vision. This single aim encompasses: rectifying and occlusion remains the mainstay and most effective , the treatment of amblyopia, and form of treatment. finally correction of the ocular deviation. As in Two other types of amblyopia treatment in almost all young children with strabismus there is a current use are penalisation and the CAM visual risk of amblyopia, treatment is directed initially stimulator. In penalisation the vision of the better towards prevention or correction of this aspect, and eye is blurred with either atropine or , or a then to the management of the deviation. Although combination of these two. It can be used in complete restoration of normal visual functions is amblyopia in the following situations: as the first often not possible, significant and worthwhile line of treatment (not common), as an alternative improvement can usually be achieved. when occlusion has failed, for maintenance of vision after successful occlusion, for recurrent amblyopia, http://adc.bmj.com/ TREATMENT OF AMBLYOPIA and for children who refuse to wear an occlusive Not all types of amblyopia behave similarly and here patch for cosmetic reasons.2 3 The CAM visual only general guidelines are included. The principle stimulator consists of a rotating high contrast grating of all modalities of amblyopia treatment is to with a transparent cover over which the child draws. promote the use of the amblyopic eye by compro- Each treatment session lasts only a few minutes. mising the vision of the better eye. This is usually Although improvement does occur this cannot be

achieved by occlusion, but other commonly used attributed to the gratings per se, but to other factors, on October 1, 2021 by guest. Protected copyright. methods include penalisation and the CAM stimula- such as minimal occlusion of the better eye during tor. Treatment should commence at as early an age treatment.23 as possible, but a prerequisite to all amblyopia treatment is a clear retinal image, and consequently TREATMENT OF SQUINT accurate optical correction is essential using either As already mentioned the aim of squint treatment is spectacles or contact lenses. the restoration of binocular function. Unfortun- Occlusion of the better eye, by an adhesive ately, particularly in comitant deviations, this is occluder, is the most commonly used method of often not possible, and the cynic could easily regard amblyopia treatment and this can be worn full time treatment as entirely cosmetic. Of course cosmesis is or part time. Full time occlusion requires careful an important goal in itself but in some paralytic monitoring as there is a danger of transient deviations normal binocular function can be re- amblyopia developing in the initially non-amblyopic stored, while in other types of squint useful but eye. Part time occlusion is generally preferred for subnormal binocular function can be achieved. In durations of 30 minutes to three hours or more. One this section the deviation will be assumed to be study that compared conventional (more than three comitant unless otherwise specified, and because of hours a day) and minimal (30 minutes) occlusion, the large range of conditions within this range and the CAM stimulator (see below) found all three treatment will only be discussed in broad terms. Arch Dis Child: first published as 10.1136/adc.64.3.413 on 1 March 1989. Downloaded from

The management of squint 417 Despite the knowledge that most squints are without for cosmetic reasons can be performed at any age any serious systemic or ocular overtones, this although the needs of an individual child will dictate possibility must not be forgotten, and before correc- the timing of this. tion of the ocular deviation is considered, the child A group which requires particular attention is that should be adequately investigated. with neurodevelopmental problems. As with all cases of strabismus the appropriate refractive cor- Nonsurgical treatment rection should be considered first otherwise the Optical-Refractive errors and squint are commonly result after surgical intervention can be associated, and for this reason every strabismic child disappointing.24 If surgery is undertaken the amount should have a meticulous mydriatic refraction. of extraocular muscle surgery necessary to achieve Spectacles are prescribed for two distinct reasons: the same result needs to be less in the retarded first to correct a visually important refractive error compared with the normal child. In the past there and to provide a clear retinal image-essential has been a general reluctance to consider cosmetic before embarking on amblyopia treatment. Second, surgery for these children, but the results can be to ensure reasonable balance between accommoda- rewarding for the child, parent, and others in daily tion and convergence. In this latter situation spec- contact.' Under these circumstances it is not the tacles are prescribed to rectify the ocular misalign- role of the surgeon to advise surgery, but simply ment and not to correct a visual deficit. Certain ensure that parents understand the various thera- deviations, such as fully accommodative esotropia, peutic options, their benefits and limitations. can be adequately controlled by spectacles, while for others the result is less satisfactory and surgery may Treatment of special types of squint-The manage- then be indicated. The effect of refractive correction ment of other types such as Duane's syndrome, depends on the age of the patient and squint type, superior oblique tendon sheath syndrome, and those but even so is often difficult to predict and it is due to muscle or orbital disease, cannot be consi- common practice to correct any 'significant' refrac- dered in detail here. Some of these conditions tive error as an initial step before embarking on produce no symptoms or little cosmetic defect (for surgery. Prisms are rarely used in paediatric practice example, most cases of Duane's syndrome) and except perhaps temporarily to control diplopia in a clearly do not require treatment, while for others paralytic squint. surgery may be considered to reduce or correct the strabismus or head posture, or increase the field of Surgical treatment binocular single vision. to Surgery align the eyes is considered for the http://adc.bmj.com/ following reasons: to cure diplopia, correct a com- pensatory head posture, or most commonly to This neurotoxin produces a temporary paralysis correct a squint either not associated with a refrac- when injected into muscle and has been used as an tive error, or when spectacles have not had the alternative to extraocular muscle surgery over the desired effect. General comments only will be past eight years. It is particularly effective in palsies, made. but has also been used in comitant deviations. To date its use in children is limited,25 26 but in the

Paralytic squint-Whether the palsy is congenital or future it may well find an important niche in the on October 1, 2021 by guest. Protected copyright. acquired, treatment is essentially surgical (having management of paediatric strabismus. first corrected any amblyopia) aiming to correct either a compensatory head posture or diplopia. For Conclusion an acquired palsy at least six months of recorded stability is mandatory before surgery is contem- While in most children squint is an isolated abnor- plated. mality, it can also be the consequence of, or associated with, a large variety of other conditions. Comitant squint-Any significant refractive error is Clinical evaluation is not always straightforward and corrected first, even in the presence of normal visual it is imperative that when there is the possibility of acuities. The adage, amblyopia correction before additional pathology the appropriate multidisciplin- surgical intervention, generally holds true and every ary assessment is adopted. In general, treatment is parent must understand that surgical alignment will directed first to the correction of amblyopia and not improve visual acuity. Surgery for infantile secondarily to the deviation itself. esotropia is generally undertaken between 6 months References and 2 years of age as correction after this time Taylor D. Screening for squint and poor vision. Arch Dis Child achieves less in terms of binocular function. Surgery 1987;62:982-3. Arch Dis Child: first published as 10.1136/adc.64.3.413 on 1 March 1989. Downloaded from

418 Fielder 2 Von Noorden GK. Burian-Von Noorden's and 15 Milot J, Guimond J. Strabismus as an expression of cerebral ocular motility. 3rd ed. St Louis: CV Mosby, 1985. motor dysfunction in childhood. Clin Pediatr 1977;16:477-9. Mein J, Harcourt B. Diagnosis and management of ocular 16 Watson AP, Fielder AR. Sudden-onset squint. Dev Med Child motility disorders. Oxford: Blackwell Scientific Publications, Neurol 1987;29:207-11. 1986. 17 Shaw DE, Fielder AR, Minshull C, Rosenthal AR. 4 Nixon RB, Helveston EM, Miller K, Archer SM, Ellis FD. Amblyopia-factors influencing age at presentation. Lancet Incidence of strabismus in neonates. Am J Ophthalmol 1985; 1988;ii:207-9. 100:798-801. 1 Mayer DL, Fulton AB, Rodier D. Grading and recognition 5 Von Noorden GK. A reassessment of XLIV acuities of pediatric patients. Ophthalmology 1984;91:947-53. Edward Jackson Lecture. Am J Ophthalmol 1988;105:1-10. 19 Watson PG, Sanac AS, Pickering MS. A comparison of various 6 Bixenman WW, von Noorden GK. Benign recurrent VI nerve methods of treatment of amblyopia: a block study. Trans palsy in childhood. J Pediatric Ophthalmol Strabismus 1981;18: Ophthalmol Soc UK 1985;104:319-28. 29-34. 20 Ching FC, Parks MM, Friendly DS. Practical management of 7 Kitchen WH, Ryan MM, Rickards A, et al. A longitudinal study amblyopia. J Pediatr Ophthalmol Strabismus 1986;23:12-6. of very low-birthweight infants IV. An overview of performance 21 Scott WE, Dickey CF. Stability of visual acuity in amblyopic at eight years of age. Dev Med Child Neurol 1980;22:172-88. patients after visual maturity. Graefes Arch Clin Exp Ophthal- Kushner BJ. Strabismus and amblyopia associated with regres- mol 1988;226:154-7. sed retinopathy of prematurity. Arch Ophthalmol 1982;100: 22 Flynn JT, Cassady JC. Current trends in amblyopia therapy. 256-61. Ophthalmology 1978;85:428-50. 9 Keith CG, Kitchen WH. Ocular morbidity in infants of very low 23 Keith CG, Howell ER, Mitchell DE, Smith S. Clinical trial of birth weight. Br J Ophthalmol 1983;67:302-5. the use of rotating grating patterns in the treatment of 10 Moseley MJ, Fielder AR. Light toxicity and the neonatal eye. amblyopia. Br J Ophthalmol 1980;64:597-606. Clinical Vision Sciences 1988;3:75-82. 24 Lo Cascio GP. Treatment for strabismus in cerebral palsy. Am J l lHarcourt B. Guidelines in the management of incomitant Optom Physiol Opt 1987;64:861-5. strabismus in children. In: Wybar KC, Taylor D, eds. Pediatric 25 Magoon EH. Botulinum toxin chemo-denervation for strabis- ophthalmology: current aspects. New York: Marcel Dekker Inc, mus in infants and children. J Pediatr Ophthalmol Strabismus 1983:341-54. 1984;21:1 10-3. 12 Hiles DA, Waller PH, McFarlane F. Current concepts in the 26 Scott AB. Botulinum injection treatment of congenital esotro- management of strabismus in children with cerebral palsy. Ann pia. In: Lenk-Schafer M, ed. Transactions of the sixth interna- Ophthalmol 1975;7:789-98. tional orthoptic congress. 1987:294-9. 13 Harcourt B. Strabismus affecting children with multiple handi- caps. Br J Ophthalmol 1974;58:272-80. 14 Bankes JLK. Eye defects of mentally handicapped children. Br Correspondence to Professor AR Fielder, Birmingham and Midland Med J 1974;ii:533-5. Eye Hospital, Church Street, Birmingham B3 2NS. http://adc.bmj.com/ on October 1, 2021 by guest. Protected copyright.