Child: care, health and development 1975, i , 315-324
Clinical ophthalmic assessment in visually handicapped children BRIAN H A R C O U R T Consultant Ophthalmologist, Leeds General Infirmary, Leeds I Accepted for publication 17 June 1975
All forms of functional assessment in early life involve a difficxilty in communication with the young subject and therefore an increased reliance upon objective methods of examination which may be augmented by information gained from the parents' history. During normal development a child passes through three stages with regard to sensory functional assessment. In the first of these the subject is entirely uncooperative so that examination is completely objective and does not differ in principle from that used in veterinary practice. In the second stage the subject is cooperative but is illiterate and understands only simple instructions so that much information has still to be obtained by objective methods, although some simple subjective tests of function can also be used. In the third stage the child is literate and techniques of examination do not differ significantly from those used for adult patients. The age at which any particular child progresses from one stage to the next in this sequence depends on his stage of general development and not upon his chronological age, although most normal children move from stage one to stage two at about the age of 3 years. Visually handicapped children always show some retardation of general development in the first few years of life so that it is rarely possible to test their vision accurately by subjective methods until somewhat later. Of course, the earlier that an accurate clinical assessment can be carried out, combined whenever necessary with the electrophysiological investigations to be described later, the earlier can decisions regarding management, visual prognosis and genetic coimselling, based on exact diagnosis be made. Satisfactory examination of young cliildren who are suspected of having poor vision is impossible in busy ophthalmic outpatient clinics, and time has to be set aside specifically for examination of each such child at leisure in quiet surroundings. Even with these precautions taken, there are some children who appear to be visually unresponsive when examined in the first few weeks of life who yet on re-examination at a later stage demonstrate normal D
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vision. The clinician should therefore always hesitate before giving a gloomy visual prognosis immediately after examination in the neonatal period unless there are incontrovertible signs of severe bilateral ophthalmic disorder.
ENTIRELY OBJECTIVE OPHTHALMIC EXAMINATION
When the child to be examined cannot cooperate with any subjective tests of visual function all the infonnation to be gained about his ability to see must be made indirectly either from objective clinical observation or from the parents' history of the child's visual responses. As visual defects in this young age group are commonly the result of genetically determined disorders, or are related to adverse antenatal factors or perinatal disorders, details of the family history, of the pregnancy, of the birth and of neonatal development are all important in supplementing the findings on clinical examination. Direct questioning of the parents regarding their child's visual behaviour at home may also be valuable. Does the cliild appear to use his eyes as well as do his peers ? Do the visual responses appear to have deteriorated after a good beginning ? From memory, do the parents think that this child has as good vision as their older children did at a similar age ? A discussion of the child's reactions in certain situations is also important. Young babies dislike bright light from birth, but within a week they will normally show a positive response to soft daylight and will tum their head and eyes towards a diffusely lit window as their bodies are nimed away from the light while they are being carried (window test). More likely the mother may have noticed the fixation of her baby's eyes upon her own eyes and face, especially during feeding. This is one of the earliest positive visual responses to develop and in the alert eyes-open stage during feeding the baby will follow binocularly the movements of his mother's face and eyes from the age of 6 weeks. These responses may be looked upon as early 'visual milestones', and they are normally followed by the development of steady sustained convergence of the eyes upon objects held in the hands by the age of 6 months. The recognition of food and of the parents by sight is normally noted around the same time, while the 9-monthsold child picks up coloured threads and similar small objects, and in the second year of life shows interest in aeroplanes and fiying birds, avoids obstacles when walking and likes the television. In seeking evidence of defective vision from external inspection of the young child, three features which may be immediately apparent are of great importance; these are pendular nystagmus or roving eye movements, photophobia and eye rubbing. Pendular nystagmus is a rhythmic involuntary rapid
Clinical ophthalmic assessment in visually handicapped children
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to-and-fro movement of the eyes about the point of fixation which is equal in amplitude and velocity in each direction, and is due either to some abnormality in the steady fixation central control mechanism (often occurring as an isolated functional defect noted from birth and hereditary in origin), or is an early acquired phenomenon resulting from a poor visual sensory input, and in yoting babies it is clinically difficult to discriminate these movements from the more random searching movements of the eyes which may aflFect the blind child. By the age of 6 weeks from birth at term a normal child has ceased to exhibit random imcoordinated eye movements and is moving the eyes binocularly over a wide range, both saccadic and pursuit movements being smooth and rapid. During the first years of life the binocular fixation reflexes become increasingly well grounded, and if the vision of both eyes fails after the age of 6 years nystagmus does not develop in any patient, and a decreasing proportion of new cases of severe visual handicap developing between birth and 6 years show the abnormahty. There is some disagreement as to whether such nystagmus once established can ever be truly reversed by prompt treatment of the causative ophthalmic disorder, such as glaucoma or cataracts; some sturgeons suggest that reversal is possible, whereas others consider that the nystagmus is an outward sign of the irreversible stimulus deprivation amblyopia developed in early life in such cases. This process, the result of insufficient stimulation of the visual apparatus during the critical formative period, which is approximately up to 4 weeks from birth in the cat, to 2 months in the monkey, but probably as long as 4 years in man, leads to anatomical and physiological derangement of the afferent visual pathways and of the visual cortex, and to an irreversible decrease in visual function which accounts for the poor visual results obtained in later hfe by technically successful surgery of dense congenital corneal opacities and cataracts. Photophobia is a prominent symptom in a number of serious ocular disorders occurring in early childhood; congenital glaucoma causes abnormal sensitivity to light because of the presence of corneal oedema which breaks down the corneal epithelial cells, while a similar sensitivity also occurs for unknown reasons in babies suffering from Leber's amaurosis, one of the commonest hereditary causes of blindness in childhood, in which the appearance of the eyes are otherwise essentially normal in the neonatal period. These babies also exhibit eye-rubbing a habit which is quite characteristic and which appears to give the child pleasure perhaps from the stimulation of phosphenes (tinformed visual hallucinations), but which can in some cases lead to very serious complications such as acute keratoconus and even perforation of the eye. Proceeding to closer inspection of the eyes themselves, an estimation
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of the corneal diameters is an important initial observation. When microphthalmos or buphtiialmos are bilateral and symmetrical and are not present to a very marked degree they may be easily overlooked, and yet they are of great diagnostic importance. The normal horizontal corneal diameter is i i mm and this does not change significantly from the time of birth. Any disorder of early ocular development such as coloboma, persistent hyperplasdc primary vitreous or cataract may be associated with microphthalmos, while buphthalmos is the hallmark of congenital and infantile glaucoma when the increase in the corneal diameter is usually associated with corneal clouding from epithelial oedema. For examination of the anterior segments of the eyes, of the range of ocular movements and of the fields of vision, a prefocused torch with an easily applied switch is most useful; the infant's attention is stimulated by the flashing light, and the steadiness of fixation and following movements can then be assessed. The range of ocular movements can be established and also the presence or absence of manifest squint, both by observation of the symmetry of the reflections of light from the cornea of each eye and of any deviation on cover-testing each eye in turn. The cover test also demonstrates any marked difference in the visual acuity of the two eyes; if fixation is steady and the child smiles when one eye is covered, but fixation is wandering and the child cries when the opposite eye is covered, then this is very good clinical evidence of a imilateral severe visual defect. When cover-testing gives equivocal tesults, observation of the corneal reflections of the examination light gives quite useful information about a possible squint; if the reflections are symmetrical no manifest squint is present, whereas the reflection from a convergent squinting eye is deviated to the temporal side of the pupil, and so on. Many young children appear to sqtaint on account of epicanthic folds which hide the sclera nasal to the cornea, producing an optical illusion of convergent squint, but in these cases the corneal reflections are central and symmetrical. An absence of squint infers the normal development of binocular function, but this can be tested for objectively and positively using the phenomenon of prism vergence. When a base-out prism (usually one of about 15 prism-dioptres strength is used) is placed before one eye it deviates the entering light rays temporally, and produces double vision. In order for binocular vision to be restored the eye behind the prism deviates inwards, and this vergence response is noted by the observer. This is an excellent test which can often be elicited in normal children from the age of about 6 months. The significance of squint in early childhood is worth discussing in more detail at this stage; squint is the result of some abnormality in the binocular fixation reflexes which are built up during the first few years of life. If the
Clinical ophthalmic assessment in visually handicapped children
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defect is in the efferent motor side of the reflex, the squint will be of the paralytic or incomitant type with some defect in the range of ocular movements (although in cases of congenital squint the movements may later become much more symmetrical). Very poor vision of one eye will produce a sensory squint because of a lack of stimulus for fusion and binocular function; the range of ocular movements will be full in such a concomitant squint, which is usually of the convergent type in childhood, and the deviation will constandy aflfect the blind eye only, being then an important external sign of serious ocular disease such as retinoblastoma, or of optic nerve disorder. However, by far the most common cause of squint in childhood is a derangement of accommodation and convergence due to refractive error, and a concomitant convergent squint, increasing in angle with accommodation upon near targets and associated with hypermetropia is the variety most commonly observed, with an onset usually after the age of i year. That motor and sensory squints are both commoner in children with neurological disorders than in the normal population is not surprising, but there is also an excess of hypermetropes among brain-damaged children, with an increased risk of the develment of accommodative squint, especially as binocular functional capacity in such children is more likely to be impaired. The examination light should next be used to examine the pupillary light reflexes. These are present from birth, but are often difficult to elicit except in dimly lit surroundings because of the small resting size of the baby's pupils. The presence of normal pupillary light reflexes does not, of course, necessarily imply the presence of normal vision as the reflex is subcortical and a child with cerebral blindness will therefore show normal reactions. However, the absence, or marked attenuation of the responses is good objective evidence of afferent visual pathway disorder either at the level of the optic nerves or within the eyes themselves. Asymmetry in response between one eye and the other is also a good guide to a unilateral visual defect of severe degree. Subtle differences between the responses of the two pupils inferring such a unilateral defect may be observed from the Marcus Gunn pupillary escape phenomenon; when the light stimulus is directed flrst at the normal eye and then rapidly transferred to the abnormal eye, the pupil of the latter eye dilates, apparently paradoxically, for its direct light reflex is weaker than its consensual reflex. In doing these tests it is important that the light is shone directly on to the pupil without an observed preliminary approach of the torch towards the eyes, otherwise the pupillary constriction associated with the accommodative response may be wrongly interpreted as a pupillary light reflex. Torchlight should also be used, in a darkened room, to assess the degree
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of iris pigmentation. Ocular albinism is confined to the eyes and the diagnosis rests mainly upon the findings of abnormal iris translucency, principally in its peripheral portion as noted by transillumination, and this is also present to some degree in female carriers of this X-Hnked genetic disorder. . It is important to assess the extent of the fields of vision as well as the aaiity of vision, and this can be done most simply by introducing a visually stimulating target into the periphery of the visual fields from various directions, noting the refixation of the eyes upon the target when the subject sees and is interested by it. It is always difficult to assess the visual function of each eye individually in the very yoimg because of their resentment of uniocular occlusion, but the defect of homonymous hemianopia can be elicited with both eyes open, and is common in children with congenital or infantile hemiplegia, aflFecting the same side. Homonymous defects can also be investigated by using two visually stimulating targets. When interest and fixation are concentrated upon one target, a second is introduced from the suspected blind side; if homonymous hemianopia is present a change of fixation on to the new target can be expected when this crosses the midline into the normal halves of the visual fields. In all these tests it is important that the visually stimulating targets used (such as coloured and white balls, or toys) are silent, for even a blind child may move the eyes towards an interesting noise using a subcortical visuostatic response, and this can be wrongly interpreted as evidence of sight. In the same way a withdrawal response to threat may be a subcortical response. Some quantitative objective assessment of visual acuity in infants can be made by varying the size of the visual targets, such as rolling white balls, or more simply sweets or strands of wool, and noting the smallest size of target which elicits a positive response, although this is an inexact method. The use of optokinetic responses has also been recommended in this regard, moving stripes or dots across the visual panorama and noting the nystagmus which these repetitive stimuli induce. Optokinetic stimuli are certainly useful as a very strong visual stimulus for an otherwise visually imresponsive child, but used as a quantitative method in the very young they suffer from clinical clumsiness, and non-responders are very common, so that such apparatus has never gained an accepted place in clinical practice. In order to examine the internal ocular structures in any detail it is necessary to dilate the pupils using a short-acting mydriatic such as cyclopentolate 0-5% eye drops. Some powerful sympathomimetic mydriatic agents such as phenylephrine 10% should not be used in young babies because of the sideeffects sometimes produced from systemic absorption; but weaker parasympatholytic agents have no significant side-effects, and except in rare cases
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where dilating the pupils may mask acute neurological complications, shotild always be used by paediatricians as well as by ophthalmologists. The range of possible abnormalities to be noted is much too extensive to be discussed here, but a few points should be emphasized. Firstly, indirect ophthalmoscopy using a binocular headlight and a powerful (-1-30 D) condensing lens is very helpful for fundus examinations of the uncooperative infant. The magniflcation is much smaller (only x 2) so that a much larger portion of the fundus is visible at one time, and the optic disc and the macula can be seen together. There is also a better view of the retinal periphery, even through moderate corneal or lens opacities. However, the technique is difficult to master especially as the image is inverted. The principal causes of defective vision in early childhood in the absence of marked opacification of the ocular media or of overt chorioretinal pathology are Leber's amaurosis and optic atrophy, and unfortunately these can be very difficult to diagnose ophthalmoscopically in infancy because they produce little deviation from normal appearances. Although Leber's amaurosis later leads on to the development of abnormal retinal pigmentation and appearances rather similar to those seen in cases of retinitis pigmentosa, this is not the case in the flrst few years of life even though vision at ±at stage is already very seriously defective. The fundus background colour is, however, often paler than is usual, although not as pale as is the case in albinos, and this is associated at an early stage with attenuation in the calibre of the retinal arteries which should always be carefully estimated in relation to that of the accompanying retinal veins. The optic discs are normally rather pale in young children, and when the two discs are similar in appearance the distinction between physiological and pathological pallor may be difficult to make with any certainty, whereas a distinction between the two discs in cases of unilateral defect is much more easily distinguished. A retinoscopy under cycloplegia should be carried out at this stage, for a marked unilateral refractive error may alter the symmetry of the disc appearances in the absence of any other pathology. It is important to assess the size as well as the colour of the optic discs; hypoplasia of the optic discs and nerves is a not uncommon cause of visual defect in infancy, and again is much easier to note as a unilateral than as a bilateral symmetrical defect. The small disc is always surrounded by a faint halo outline of the normal disc size. As h5rpoplasia of the optic nerves may be associated with important midline cerebral defects, some of which can give rise to treatable growth hormone deficiency dwarfism, it is clearly most important that the diagnosis should not be missed. Macular degenerative changes often produce only subtle variations in ophthalmoscopic appearances in early life, and in order to assess these and
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other changes fully an examination under general anaesthesia may be necessary, and this can be combined with electroretinography, an investigation which is vital in diagnosing and assessing certain retinal degenerations. This objective electrophysiological investigation and that of the assessment of visually evoked cortical resonses are most necessary in those cases in which the eyes appear relatively or completely normal, but in which there are poor clinical visual responses. When the defect is due to widespread retinal aplasia the electroretinogram is absent, whereas in severe optic atrophy or in cerebral blindness this response is of normal amplitude, whereas the visually evoked responses are subnormal. Only in those cases in which the visual apparatus is intact, but in which the infant is clinically unresponsive due to a lack of interest in visual stimuli, usually only as one aspect of a global retardation, is it likely that the electrophysiological responses will be normal, and the outlook for the later development of useful vision is much less gloomy in such cases. In summary, the diagnosis of poor vision in one or both eyes of an infant has to be made by inference, and squint, resentment of occlusion of one eye but not of the other and asymmetry of the pupillary light reflexes are the best external indicators in unilateral cases. When there is very poor vision in both eyes, nystagmus or searching movements are most significant, in addition to the child's general behaviour.
SIMPLE SUBJECTIVE OPHTHALMIC EXAMINATION
When subjects reach an age and a stage of development at which they can cooperate with simple subjective tests of visual function, there can be no doubt that the letter-matching tests developed by Dr Mary Sheridan (STYCAR tests) come nearest to fulfilling all the theoretical requirements of an illiterate simple visual acuity test, and the method is too familiar to require description in detail. Certain points, however, are particularly important; the resolving power of the eyes varies not only with refraction and with the health of the optical apparatus, but with the intensity of illumination of the test letters, and this must be adequate when the assessment is done. A nearequivalent of the test for use at one-third of a metre is also useful, as a knowledge of the reading vision potential, particularly in children with nystagmus, is an important factor in deciding whether a child is capable of normal-sighted education. The visual acuities should, of course, be tested with the subject wearing appropriate glasses when there is a significant refractive error. Again, it is much easier to test accurately the vision of the two eyes together, than of each individual eye in young children, and from an education aspect, though
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not from a clinical point of view, this is the only really important information. In comparing the vision of one eye with that of the other, for instance when
treating by occlusion small degrees of amblyopia, it is important to use lines of letters rather than single letters for the letter-matching tests. If this is not
done, the 'crowding' effect of lines of letters on either side of the particular letter to be recognized which occurs in amblyopic eyes will be missed; in such cases a single-letter visual acuity of 6/9 may, using lines of letters, be only 6/18. For children who have a marked visual handicap, the Sheridan PANDA tests using much larger letters and orientated stripes as the test material will accurately assess visual acuities as low as 1/60, but the principles of the tests are no different from those of the STYCAR letter tests. Cut-out polystyrene letters arranged before the child enable him to head-point at the matching letter if physical handicap makes it impossible for him to finger-point accurately. At this stage of development colour vision also can be tested, and this is particularly important in cases of suspected cone degeneration syndrome, optic neuritis and optic atrophy, especially the dominant hereditary form. Pseudoisochromatic plates should be used, and the most convenient of these is the American Optical Company Hardy-Rand-Rittler (H-R-R) test using simple symbols as the test objects with a matching key card. This test grades the severity of any deficiency in colour discrimination and also investigates the blue-yeUow as well as the red-green part of the spectrum. Ishihara tests are less satisfactory, but can be used if the child traces the figure or the wavy line with afinger,or the test can be modified as in the Gardiner test, another lettermatching procedure. There is no urgency in testing normal children's colour vision, and this can be more reliably done at the age of 8 years.
COMPLEX SUBJECTIVE OPHTHALMIC EXAMINATION
When the child is old enough or cooperative enough to carry out normal adult tests of visual function there are still certain important factors to be borne in mind. The first of these is latent nystagmus; some children show a tendency for thefixingeye to become unsteady when the other eye is occluded, so that the vision as tested with each eye individually is poor, whereas the vision with the two eyes tested together is normal. Binocular testing should therefore always be done, and the fixation of the eyes observed, before a child is declared to have poor vision in each eye as the result of Snellen chart vision testing. Latent nystagmus tends to decrease spontaneously with the passage of time and this problem in vision testing is not noted in adult patients.
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Secondly, because of tiieir very active accommodation, children may make themselves sptiriously myopic when they stare hard at a row of small Snellen letters, and the distance visual acuity may then vary dtaring the testing and appear to be defective. When this is the case and there are also symptoms of variable difl&culties with distance vision, a refraction tinder cycloplegia to eliminate the efFect of accommodation should always be carried out. Finally, the visually handicapped child should wear any appropriate low-visual aid in addition to his refractive correction when assessments, especially of near vision, are made. Testing visual ftmction in childhood, particularly when it is defective, and drawing conclusions about the cause of the defect from the result of clinical examination are inextricably interwoven procedures, and long practice is required in order that all those tests which are especially appropriate to a particular patient are used,.and that neither too little nor too much is asked of the young subject.
Clinical ophthalmic assessment in visually handicapped children BRIAN H A R C O U R T Consultant Ophthalmologist, Leeds General Infirmary, Leeds I Accepted for publication 17 June 1975
All forms of functional assessment in early life involve a difficxilty in communication with the young subject and therefore an increased reliance upon objective methods of examination which may be augmented by information gained from the parents' history. During normal development a child passes through three stages with regard to sensory functional assessment. In the first of these the subject is entirely uncooperative so that examination is completely objective and does not differ in principle from that used in veterinary practice. In the second stage the subject is cooperative but is illiterate and understands only simple instructions so that much information has still to be obtained by objective methods, although some simple subjective tests of function can also be used. In the third stage the child is literate and techniques of examination do not differ significantly from those used for adult patients. The age at which any particular child progresses from one stage to the next in this sequence depends on his stage of general development and not upon his chronological age, although most normal children move from stage one to stage two at about the age of 3 years. Visually handicapped children always show some retardation of general development in the first few years of life so that it is rarely possible to test their vision accurately by subjective methods until somewhat later. Of course, the earlier that an accurate clinical assessment can be carried out, combined whenever necessary with the electrophysiological investigations to be described later, the earlier can decisions regarding management, visual prognosis and genetic coimselling, based on exact diagnosis be made. Satisfactory examination of young cliildren who are suspected of having poor vision is impossible in busy ophthalmic outpatient clinics, and time has to be set aside specifically for examination of each such child at leisure in quiet surroundings. Even with these precautions taken, there are some children who appear to be visually unresponsive when examined in the first few weeks of life who yet on re-examination at a later stage demonstrate normal D
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vision. The clinician should therefore always hesitate before giving a gloomy visual prognosis immediately after examination in the neonatal period unless there are incontrovertible signs of severe bilateral ophthalmic disorder.
ENTIRELY OBJECTIVE OPHTHALMIC EXAMINATION
When the child to be examined cannot cooperate with any subjective tests of visual function all the infonnation to be gained about his ability to see must be made indirectly either from objective clinical observation or from the parents' history of the child's visual responses. As visual defects in this young age group are commonly the result of genetically determined disorders, or are related to adverse antenatal factors or perinatal disorders, details of the family history, of the pregnancy, of the birth and of neonatal development are all important in supplementing the findings on clinical examination. Direct questioning of the parents regarding their child's visual behaviour at home may also be valuable. Does the cliild appear to use his eyes as well as do his peers ? Do the visual responses appear to have deteriorated after a good beginning ? From memory, do the parents think that this child has as good vision as their older children did at a similar age ? A discussion of the child's reactions in certain situations is also important. Young babies dislike bright light from birth, but within a week they will normally show a positive response to soft daylight and will tum their head and eyes towards a diffusely lit window as their bodies are nimed away from the light while they are being carried (window test). More likely the mother may have noticed the fixation of her baby's eyes upon her own eyes and face, especially during feeding. This is one of the earliest positive visual responses to develop and in the alert eyes-open stage during feeding the baby will follow binocularly the movements of his mother's face and eyes from the age of 6 weeks. These responses may be looked upon as early 'visual milestones', and they are normally followed by the development of steady sustained convergence of the eyes upon objects held in the hands by the age of 6 months. The recognition of food and of the parents by sight is normally noted around the same time, while the 9-monthsold child picks up coloured threads and similar small objects, and in the second year of life shows interest in aeroplanes and fiying birds, avoids obstacles when walking and likes the television. In seeking evidence of defective vision from external inspection of the young child, three features which may be immediately apparent are of great importance; these are pendular nystagmus or roving eye movements, photophobia and eye rubbing. Pendular nystagmus is a rhythmic involuntary rapid
Clinical ophthalmic assessment in visually handicapped children
317
to-and-fro movement of the eyes about the point of fixation which is equal in amplitude and velocity in each direction, and is due either to some abnormality in the steady fixation central control mechanism (often occurring as an isolated functional defect noted from birth and hereditary in origin), or is an early acquired phenomenon resulting from a poor visual sensory input, and in yoting babies it is clinically difficult to discriminate these movements from the more random searching movements of the eyes which may aflFect the blind child. By the age of 6 weeks from birth at term a normal child has ceased to exhibit random imcoordinated eye movements and is moving the eyes binocularly over a wide range, both saccadic and pursuit movements being smooth and rapid. During the first years of life the binocular fixation reflexes become increasingly well grounded, and if the vision of both eyes fails after the age of 6 years nystagmus does not develop in any patient, and a decreasing proportion of new cases of severe visual handicap developing between birth and 6 years show the abnormahty. There is some disagreement as to whether such nystagmus once established can ever be truly reversed by prompt treatment of the causative ophthalmic disorder, such as glaucoma or cataracts; some sturgeons suggest that reversal is possible, whereas others consider that the nystagmus is an outward sign of the irreversible stimulus deprivation amblyopia developed in early life in such cases. This process, the result of insufficient stimulation of the visual apparatus during the critical formative period, which is approximately up to 4 weeks from birth in the cat, to 2 months in the monkey, but probably as long as 4 years in man, leads to anatomical and physiological derangement of the afferent visual pathways and of the visual cortex, and to an irreversible decrease in visual function which accounts for the poor visual results obtained in later hfe by technically successful surgery of dense congenital corneal opacities and cataracts. Photophobia is a prominent symptom in a number of serious ocular disorders occurring in early childhood; congenital glaucoma causes abnormal sensitivity to light because of the presence of corneal oedema which breaks down the corneal epithelial cells, while a similar sensitivity also occurs for unknown reasons in babies suffering from Leber's amaurosis, one of the commonest hereditary causes of blindness in childhood, in which the appearance of the eyes are otherwise essentially normal in the neonatal period. These babies also exhibit eye-rubbing a habit which is quite characteristic and which appears to give the child pleasure perhaps from the stimulation of phosphenes (tinformed visual hallucinations), but which can in some cases lead to very serious complications such as acute keratoconus and even perforation of the eye. Proceeding to closer inspection of the eyes themselves, an estimation
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of the corneal diameters is an important initial observation. When microphthalmos or buphtiialmos are bilateral and symmetrical and are not present to a very marked degree they may be easily overlooked, and yet they are of great diagnostic importance. The normal horizontal corneal diameter is i i mm and this does not change significantly from the time of birth. Any disorder of early ocular development such as coloboma, persistent hyperplasdc primary vitreous or cataract may be associated with microphthalmos, while buphthalmos is the hallmark of congenital and infantile glaucoma when the increase in the corneal diameter is usually associated with corneal clouding from epithelial oedema. For examination of the anterior segments of the eyes, of the range of ocular movements and of the fields of vision, a prefocused torch with an easily applied switch is most useful; the infant's attention is stimulated by the flashing light, and the steadiness of fixation and following movements can then be assessed. The range of ocular movements can be established and also the presence or absence of manifest squint, both by observation of the symmetry of the reflections of light from the cornea of each eye and of any deviation on cover-testing each eye in turn. The cover test also demonstrates any marked difference in the visual acuity of the two eyes; if fixation is steady and the child smiles when one eye is covered, but fixation is wandering and the child cries when the opposite eye is covered, then this is very good clinical evidence of a imilateral severe visual defect. When cover-testing gives equivocal tesults, observation of the corneal reflections of the examination light gives quite useful information about a possible squint; if the reflections are symmetrical no manifest squint is present, whereas the reflection from a convergent squinting eye is deviated to the temporal side of the pupil, and so on. Many young children appear to sqtaint on account of epicanthic folds which hide the sclera nasal to the cornea, producing an optical illusion of convergent squint, but in these cases the corneal reflections are central and symmetrical. An absence of squint infers the normal development of binocular function, but this can be tested for objectively and positively using the phenomenon of prism vergence. When a base-out prism (usually one of about 15 prism-dioptres strength is used) is placed before one eye it deviates the entering light rays temporally, and produces double vision. In order for binocular vision to be restored the eye behind the prism deviates inwards, and this vergence response is noted by the observer. This is an excellent test which can often be elicited in normal children from the age of about 6 months. The significance of squint in early childhood is worth discussing in more detail at this stage; squint is the result of some abnormality in the binocular fixation reflexes which are built up during the first few years of life. If the
Clinical ophthalmic assessment in visually handicapped children
319
defect is in the efferent motor side of the reflex, the squint will be of the paralytic or incomitant type with some defect in the range of ocular movements (although in cases of congenital squint the movements may later become much more symmetrical). Very poor vision of one eye will produce a sensory squint because of a lack of stimulus for fusion and binocular function; the range of ocular movements will be full in such a concomitant squint, which is usually of the convergent type in childhood, and the deviation will constandy aflfect the blind eye only, being then an important external sign of serious ocular disease such as retinoblastoma, or of optic nerve disorder. However, by far the most common cause of squint in childhood is a derangement of accommodation and convergence due to refractive error, and a concomitant convergent squint, increasing in angle with accommodation upon near targets and associated with hypermetropia is the variety most commonly observed, with an onset usually after the age of i year. That motor and sensory squints are both commoner in children with neurological disorders than in the normal population is not surprising, but there is also an excess of hypermetropes among brain-damaged children, with an increased risk of the develment of accommodative squint, especially as binocular functional capacity in such children is more likely to be impaired. The examination light should next be used to examine the pupillary light reflexes. These are present from birth, but are often difficult to elicit except in dimly lit surroundings because of the small resting size of the baby's pupils. The presence of normal pupillary light reflexes does not, of course, necessarily imply the presence of normal vision as the reflex is subcortical and a child with cerebral blindness will therefore show normal reactions. However, the absence, or marked attenuation of the responses is good objective evidence of afferent visual pathway disorder either at the level of the optic nerves or within the eyes themselves. Asymmetry in response between one eye and the other is also a good guide to a unilateral visual defect of severe degree. Subtle differences between the responses of the two pupils inferring such a unilateral defect may be observed from the Marcus Gunn pupillary escape phenomenon; when the light stimulus is directed flrst at the normal eye and then rapidly transferred to the abnormal eye, the pupil of the latter eye dilates, apparently paradoxically, for its direct light reflex is weaker than its consensual reflex. In doing these tests it is important that the light is shone directly on to the pupil without an observed preliminary approach of the torch towards the eyes, otherwise the pupillary constriction associated with the accommodative response may be wrongly interpreted as a pupillary light reflex. Torchlight should also be used, in a darkened room, to assess the degree
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of iris pigmentation. Ocular albinism is confined to the eyes and the diagnosis rests mainly upon the findings of abnormal iris translucency, principally in its peripheral portion as noted by transillumination, and this is also present to some degree in female carriers of this X-Hnked genetic disorder. . It is important to assess the extent of the fields of vision as well as the aaiity of vision, and this can be done most simply by introducing a visually stimulating target into the periphery of the visual fields from various directions, noting the refixation of the eyes upon the target when the subject sees and is interested by it. It is always difficult to assess the visual function of each eye individually in the very yoimg because of their resentment of uniocular occlusion, but the defect of homonymous hemianopia can be elicited with both eyes open, and is common in children with congenital or infantile hemiplegia, aflFecting the same side. Homonymous defects can also be investigated by using two visually stimulating targets. When interest and fixation are concentrated upon one target, a second is introduced from the suspected blind side; if homonymous hemianopia is present a change of fixation on to the new target can be expected when this crosses the midline into the normal halves of the visual fields. In all these tests it is important that the visually stimulating targets used (such as coloured and white balls, or toys) are silent, for even a blind child may move the eyes towards an interesting noise using a subcortical visuostatic response, and this can be wrongly interpreted as evidence of sight. In the same way a withdrawal response to threat may be a subcortical response. Some quantitative objective assessment of visual acuity in infants can be made by varying the size of the visual targets, such as rolling white balls, or more simply sweets or strands of wool, and noting the smallest size of target which elicits a positive response, although this is an inexact method. The use of optokinetic responses has also been recommended in this regard, moving stripes or dots across the visual panorama and noting the nystagmus which these repetitive stimuli induce. Optokinetic stimuli are certainly useful as a very strong visual stimulus for an otherwise visually imresponsive child, but used as a quantitative method in the very young they suffer from clinical clumsiness, and non-responders are very common, so that such apparatus has never gained an accepted place in clinical practice. In order to examine the internal ocular structures in any detail it is necessary to dilate the pupils using a short-acting mydriatic such as cyclopentolate 0-5% eye drops. Some powerful sympathomimetic mydriatic agents such as phenylephrine 10% should not be used in young babies because of the sideeffects sometimes produced from systemic absorption; but weaker parasympatholytic agents have no significant side-effects, and except in rare cases
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where dilating the pupils may mask acute neurological complications, shotild always be used by paediatricians as well as by ophthalmologists. The range of possible abnormalities to be noted is much too extensive to be discussed here, but a few points should be emphasized. Firstly, indirect ophthalmoscopy using a binocular headlight and a powerful (-1-30 D) condensing lens is very helpful for fundus examinations of the uncooperative infant. The magniflcation is much smaller (only x 2) so that a much larger portion of the fundus is visible at one time, and the optic disc and the macula can be seen together. There is also a better view of the retinal periphery, even through moderate corneal or lens opacities. However, the technique is difficult to master especially as the image is inverted. The principal causes of defective vision in early childhood in the absence of marked opacification of the ocular media or of overt chorioretinal pathology are Leber's amaurosis and optic atrophy, and unfortunately these can be very difficult to diagnose ophthalmoscopically in infancy because they produce little deviation from normal appearances. Although Leber's amaurosis later leads on to the development of abnormal retinal pigmentation and appearances rather similar to those seen in cases of retinitis pigmentosa, this is not the case in the flrst few years of life even though vision at ±at stage is already very seriously defective. The fundus background colour is, however, often paler than is usual, although not as pale as is the case in albinos, and this is associated at an early stage with attenuation in the calibre of the retinal arteries which should always be carefully estimated in relation to that of the accompanying retinal veins. The optic discs are normally rather pale in young children, and when the two discs are similar in appearance the distinction between physiological and pathological pallor may be difficult to make with any certainty, whereas a distinction between the two discs in cases of unilateral defect is much more easily distinguished. A retinoscopy under cycloplegia should be carried out at this stage, for a marked unilateral refractive error may alter the symmetry of the disc appearances in the absence of any other pathology. It is important to assess the size as well as the colour of the optic discs; hypoplasia of the optic discs and nerves is a not uncommon cause of visual defect in infancy, and again is much easier to note as a unilateral than as a bilateral symmetrical defect. The small disc is always surrounded by a faint halo outline of the normal disc size. As h5rpoplasia of the optic nerves may be associated with important midline cerebral defects, some of which can give rise to treatable growth hormone deficiency dwarfism, it is clearly most important that the diagnosis should not be missed. Macular degenerative changes often produce only subtle variations in ophthalmoscopic appearances in early life, and in order to assess these and
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other changes fully an examination under general anaesthesia may be necessary, and this can be combined with electroretinography, an investigation which is vital in diagnosing and assessing certain retinal degenerations. This objective electrophysiological investigation and that of the assessment of visually evoked cortical resonses are most necessary in those cases in which the eyes appear relatively or completely normal, but in which there are poor clinical visual responses. When the defect is due to widespread retinal aplasia the electroretinogram is absent, whereas in severe optic atrophy or in cerebral blindness this response is of normal amplitude, whereas the visually evoked responses are subnormal. Only in those cases in which the visual apparatus is intact, but in which the infant is clinically unresponsive due to a lack of interest in visual stimuli, usually only as one aspect of a global retardation, is it likely that the electrophysiological responses will be normal, and the outlook for the later development of useful vision is much less gloomy in such cases. In summary, the diagnosis of poor vision in one or both eyes of an infant has to be made by inference, and squint, resentment of occlusion of one eye but not of the other and asymmetry of the pupillary light reflexes are the best external indicators in unilateral cases. When there is very poor vision in both eyes, nystagmus or searching movements are most significant, in addition to the child's general behaviour.
SIMPLE SUBJECTIVE OPHTHALMIC EXAMINATION
When subjects reach an age and a stage of development at which they can cooperate with simple subjective tests of visual function, there can be no doubt that the letter-matching tests developed by Dr Mary Sheridan (STYCAR tests) come nearest to fulfilling all the theoretical requirements of an illiterate simple visual acuity test, and the method is too familiar to require description in detail. Certain points, however, are particularly important; the resolving power of the eyes varies not only with refraction and with the health of the optical apparatus, but with the intensity of illumination of the test letters, and this must be adequate when the assessment is done. A nearequivalent of the test for use at one-third of a metre is also useful, as a knowledge of the reading vision potential, particularly in children with nystagmus, is an important factor in deciding whether a child is capable of normal-sighted education. The visual acuities should, of course, be tested with the subject wearing appropriate glasses when there is a significant refractive error. Again, it is much easier to test accurately the vision of the two eyes together, than of each individual eye in young children, and from an education aspect, though
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not from a clinical point of view, this is the only really important information. In comparing the vision of one eye with that of the other, for instance when
treating by occlusion small degrees of amblyopia, it is important to use lines of letters rather than single letters for the letter-matching tests. If this is not
done, the 'crowding' effect of lines of letters on either side of the particular letter to be recognized which occurs in amblyopic eyes will be missed; in such cases a single-letter visual acuity of 6/9 may, using lines of letters, be only 6/18. For children who have a marked visual handicap, the Sheridan PANDA tests using much larger letters and orientated stripes as the test material will accurately assess visual acuities as low as 1/60, but the principles of the tests are no different from those of the STYCAR letter tests. Cut-out polystyrene letters arranged before the child enable him to head-point at the matching letter if physical handicap makes it impossible for him to finger-point accurately. At this stage of development colour vision also can be tested, and this is particularly important in cases of suspected cone degeneration syndrome, optic neuritis and optic atrophy, especially the dominant hereditary form. Pseudoisochromatic plates should be used, and the most convenient of these is the American Optical Company Hardy-Rand-Rittler (H-R-R) test using simple symbols as the test objects with a matching key card. This test grades the severity of any deficiency in colour discrimination and also investigates the blue-yeUow as well as the red-green part of the spectrum. Ishihara tests are less satisfactory, but can be used if the child traces the figure or the wavy line with afinger,or the test can be modified as in the Gardiner test, another lettermatching procedure. There is no urgency in testing normal children's colour vision, and this can be more reliably done at the age of 8 years.
COMPLEX SUBJECTIVE OPHTHALMIC EXAMINATION
When the child is old enough or cooperative enough to carry out normal adult tests of visual function there are still certain important factors to be borne in mind. The first of these is latent nystagmus; some children show a tendency for thefixingeye to become unsteady when the other eye is occluded, so that the vision as tested with each eye individually is poor, whereas the vision with the two eyes tested together is normal. Binocular testing should therefore always be done, and the fixation of the eyes observed, before a child is declared to have poor vision in each eye as the result of Snellen chart vision testing. Latent nystagmus tends to decrease spontaneously with the passage of time and this problem in vision testing is not noted in adult patients.
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Secondly, because of tiieir very active accommodation, children may make themselves sptiriously myopic when they stare hard at a row of small Snellen letters, and the distance visual acuity may then vary dtaring the testing and appear to be defective. When this is the case and there are also symptoms of variable difl&culties with distance vision, a refraction tinder cycloplegia to eliminate the efFect of accommodation should always be carried out. Finally, the visually handicapped child should wear any appropriate low-visual aid in addition to his refractive correction when assessments, especially of near vision, are made. Testing visual ftmction in childhood, particularly when it is defective, and drawing conclusions about the cause of the defect from the result of clinical examination are inextricably interwoven procedures, and long practice is required in order that all those tests which are especially appropriate to a particular patient are used,.and that neither too little nor too much is asked of the young subject.
