‘Visual impairment in children with brain damage: towards a diagnostic procedure?’

‘Visual impairment in children with brain damage: towards a diagnostic procedure? ’ SIR–The discussion in this journal (Vol.44: 356–357, 2002) between the Vancouver group (Carey Matsuba, James Jan, Christopher Lyons, and Roberta Heaven) and the Lausanne group (Eliane Roulet-Perez and Thierry Deonna), concerning the terms cortical versus cerebral visual impairment in children, and whether eye motility problems may or may not be covered by the term, has highlighted an important issue. Children with visual impairment due to damage to the retrogeniculate visual pathways constitute an increasing group among visually impaired children in the Western world.1 Clinicians in the paediatric field (neurologists, psychiatrists, psychologists, and ophthalmologists) need to define criteria which would include a child within this functional diagnosis, and consent on grading and description of the pattern of the visual disability. Since the 1980s, groups from USA, Canada, UK, the Netherlands, Italy, and Scandinavia, have presented studies of children with cerebral visual pathway lesions and visual function problems. In 1985, Whiting and colleagues2 demonstrated that children with permanent cortical visual impairment rarely had complete lack of vision, did not have manifest nystagmus, and that it often coexisted with abnormal optic disc appearance, presumably the result of a retrograde transsynaptic degeneration. In 1987, Jan et al.3 described cortical visual impairment as severe visual loss, normal or minimal ocular finding, and clinical, electrodiagnostic, and computed tomographic (CT) evidence of post-geniculate lesions involving the visual cortex. In 1994, the same group defined cortical visual impairment as ‘bilateral loss of vision, with normal pupillary responses and an eye examination that shows no abnormalities’. 4 Research groups in Europe have chosen terms such as cerebral visual disturbance5 and cerebral visual impairment6,7 for children with retrogeniculate causes of visual dysfunction. The manifestations of this kind of visual impairment include subnormal acuity and crowding,5,8,9 affected visual fields,10 a characteristic behavioural profile, and associated disorders of higher visual processing.8 It also includes ocular motor problems,11 such as strabismus, neurological nystagmus, deficient accommodation, fixation, saccades, and smooth pursuit movements.Aetiological and morphological causes of cerebral visual impairment in young children have been described and may be malformation, hypoxia-ischemia, infection, or trauma. The pattern of pathology found depends on the stage at which the immature cerebral visual system was injured. The lesions are seldom restricted to the visual pathways but often also engage other parts of the CNS, and result in more pervasive developmental disorders. A wide range of disorders have been described in children who are visually impaired due to brain lesions, these include: uneven cognitive performances, visual-spatial and visual-motor difficulties, attention problems and autistic-like behaviours, and cerebral palsy. Varying degrees of learning problems are reported within a spectrum from severe learning disability,* to more limited areas of dysfunction in children with an intellectual ability within the normal range.8 Therefore, a child with brain damage may present many functional deficits, one of which is visual impairment. The label of the functional deficit will then depend on which dysfunction is the most conspicuous, and in whose office the child was seen. In a pre-verbal child it may not be possible to know whether observed behaviour and practical problems are the consequence of visual impairment or learning disability, or both. Although the terminology differs, there is a fair amount of agreement about the functional core deficits in children with visual impairment due to brain damage. There is a need to reach consensus on the diagnostic terminology, as well as on inclusion and exclusion criteria, and grading of the severity of the functional disability. We suggest that the term cerebral visual impairment, in keeping with the term cerebral palsy, is chosen to describe the clinical condition and functional deficit due to damage to the posterior visual pathways and/or visual cortex. The term cerebral visual impairment has been preferred to cortical visual impairment because only rarely is the cortex of the brain damaged in isolation. Furthermore, we put forward a proposal that the functional diagnosis of cerebral visual impairment should be suspected in a child who in the absence of ocular pathology, other than mildly abnormal appearance of the optic disc, demonstrates subnormal visual acuity for age (as measured with gratings or with linear optotypes [with the best correction], and/or constricted visual fields found with confrontation, Goldmann12 or computerized perimetry in combination with a disabling visual perceptual-cognitive dysfunction, as demonstrated with neuropsychological assessment and/or a structured history taking13). This condition may be aggravated by eye motility problems, such as poor fixation and/or eye movement disability. Cerebral visual impairment may be graded as mild, moderate, or severe, based on assessment of these functions. Visual perceptual-cognitive dysfunction may be suspected early but cannot be accurately assessed until the age of 4–5 years. Cerebral visual impairment may therefore be a tentative clinical diagnose at early ages. Later in life the visual acuity may improve but the visual cognitive problems persist or even increase. The diagnostic procedure demands a clinical examination of the eyes and ocular motility, and an assessment of visual perception-cognition by psychological testing and/or by structured history taking.13 The diagnosis may be strengthened by neuroimaging of the brain in order to demonstrate lesions to the visual pathways/visual cortex. Other clinical signs of brain damage, such as cerebral palsy or epilepsy, may also indicate a cerebral cause of visual dysfunction. The four children described below, illustrate how function can be evaluated with a battery of different standard techniques as a base for diagnoses. Child 1 was 9 years old, with grating acuity 12 c/d, binocular linear optotype acuity 0.15. Fields: low neural capacity (15%) measured with computer-assisted high-pass resolution perimetry, but near normal outer limits measured with Goldmann12 perimetry. WISC: Verbal IQ 120, Performance IQ 60, Full Scale IQ 100. Eye motility: esotropia, manifest nystagmus, problems with holding fixation, occurrence of paroxysmal deviations, inability to perform adequate saccades, and