Visual problems in children with brain damage

Approximately one in a thousand children aged 0-16 years is visually impaired. This represented 50 children in an average health district with a population of 250,000 (1), a significant proportion of whom has cerebral vision impairment. Children with multiple disabilities are frequently referred for refraction and assessment of visual function, so that parents and carers can be advised about and understand what the child can and cannot see.

Visual problems in children with brain damage The goals of assessment are to determine the functional vision available for communication, education, navigation and other activities, and to advise on methods of enhancement and compensation to circumvent the visual problems and enhance development for each individual child.

The History A detailed history can help compensate for what may necessarily be a limited examination in these children. The profoundly visually impaired child may show evidence of "blind sight" subserved by the collicular visual system. Such children commonly have impaired movement of all four limbs and appear to react to slowly moving targets at the side. If they are mobile, they can navigate around obstacles, but paradoxically may show little evidence of other visual functions. Severe visual impairment warrants particular enquiry concerning eye contact, and the maximum distance from which a silent smile is returned. Vision with an acuity of 6/60 or better necessitates questions directed towards identifying the following problems

Estimating Visual Function Function assessment is carried out with both eyes open. Visual behaviour is watched carefully. If the child makes eye contact, move back gradually until it is lost, in order to establish the distance within which communication must be made. The fixation pattern if the child looks around is informative. An alert child repeatedly changes the direction of gaze to fixate on different targets, whereas the child with impaired vision appears to look past the examiner with inaccurate and less frequent eye movements.

Visual acuity Visual acuity may be estimated in a number of ways, the functional significance of which needs to be distinguished. VEP acuity is the minimum target separation which permits VEP signal detection. Detection acuity (Catford drum or Stycar balls) estimates the minimum size visible. Resolution acuity (preferential looking cards) is the minimum separation which allows discrimination. Recognition acuity (letters or pictures) is the minimum size which facilitates identification.

Tests must be appropriate for age and ability. Cardiff cards afford a rapid and reproducible preferential looking test. The vertical presentation is helpful in obviating problems due to hemianopia or horizontal nystagmus and the picture format allows end point detection. Keeler cards are more suitable for infants who are severely impaired, and may need to be presented vertically if hemianopia is present or suspected. Recognition tests can give a lower visual acuity due to crowding

Functional vision As the visual acuity is a measure at maximum contrast and does not estimate functional vision, the size of educational material must be gauged to allow maximum speeds of access to information. Contrast sensitivity may be estimated using fading optotypes or in younger children, low contrast faces revealed from behind a cover*. Reduced contrast sensitivity necessitates the use of high contrast educational material. Colour vision is commonly intact although some children can match but not name colours (colour anomia). Functional visual field assessment is carried out binocularly, particularly to elicit homonymous defects. For the young child, the child's attention is attracted while a target is introduced from behind in each of the four quadrants, anticipating a head turn.

Eye movement disturbances Eye movement disturbances are common. These include nystagmus (particularly with additional optic nerve hypoplasia), gaze palsies, oculomotor apraxia and impaired tracking. The latter may cause children to have no interest in fast moving cartoons but to prefer TV programmes with limited movement.

Accommodation and convergence.Some children with brain damage have reduced or absent accommodation and therefore poor third dimensional tracking which leads to difficulty overcoming hypermetropia. Retinoscopy prior to cycloplegia can identify impaired accommodation and reveal manifest hypermetropia not corrected by the accommodative reflex. The provision of spectacles can give gratifying results.

Identification of Higher Visual Processing Disorders Observation and a thorough history may reveal and help explain some of the following types of visual problem. Simultaneous visual processing problems (are common in children with impaired movement of all four limbs and may manifest as difficulty in finding a toy on a patterned carpet. Crowding is a clinical manifestation of the disorder. Sorting out a complex visual scene can take a long time. Such children may read short words easily but can lose track with long words. Enlargement and simplification of educational material, with sequential presentation against a plain background can be recommended.

Form vision Recognition of people, shapes or objects can be selectively impaired particularly in periventrical leucomalacia. A child may be able to see a small toy in the distance but be unable to recognise a close relative in a group. Affected children compensate by voice recognition or by recognising shoes or brooches. Problems with reading are best assessed by an expert in visual impairment and education who takes into account the optimal size and lighting required for a maximum comfortable reading speed and who recognises the nature of specific reading disorders.

Problems with orientation Problems with orientation occur but are not just visual in origin. Children blind from eye disease can be adept at navigation, while children with posterior cerebral pathology (particularly on the right) may have good acuity but get lost and cannot find their toys. Limited mobility and constant supervision do not give opportunities to develop navigational skills. Education strategies and mobility training which compensate by using, for example, language memory for standard routes, are essential.

Other impairments Perception of movement is most commonly impaired on account of impaired tracking, but can rarely be a problem in children with damage to the part of the brain responsible for movement perception, area V5 (5.10). Visual memory is used for copying tasks which can prove difficult for children with cerebral visual impairment. In new environments, affected young children may have impaired face recognition and navigation. Visual imagination is also observed by the occipital brain, and descriptions given by parents may indicate good language processing, but difficulties in handling imagined visual concepts. Lack of visual attention which is intermittent is common when tiredness, pre-occupation or distraction lead to behavioural diminution of visual function. In contract, familiarity with the environment appears to enhance visual performance. Prolongation of visual tasks is a common feature. Sufficient time should be given for a child to demonstrate his or her ability, and the reduced performance speed recognised.