Structured history taking to characterize visual dysfunction and plan optimal habilitation for children with cerebral visual impairment

Abstract

Young children with impaired vision tend to have limited awareness of their visual condition. The frame of reference for what is normal is oneself, and such children ‘know’ themselves to be ‘normal’. Many brain functions (such as visual guidance of movement and visual search) are subconscious, so that impairment is not symptomatic. If part of the brain responsible for a specific function is damaged, there may be lack of insight for the loss. Not to know is agnosia. Not to know that one does not know is anosagnosia, and most children with impaired vision on account of damage to the brain are anosagnostic for the nature and degree of their visual impairment. So they are not in a position to compensate for their visual difficulties without appropriate assistance. Vision facilitates access to information, whether it is in the distance (such as a letter box or a tree) or for near (such as toys or books), social interaction, and visual guidance of movement of the limbs and body. Visual impairment can impair all these skills, with an adverse impact on development. This applies particularly to cerebral visual impairment. Assessment of vision is carried out to assist in diagnosis, to monitor progress, and to plan the provision of optimal resources to circumvent visual difficulties. The latter is done by determining the everyday limits for each aspect of binocular functional vision (visual acuity, colour vision, contrast sensitivity, visual fields, movement perception, the degree of visual crowding, the accuracy of visual guidance of movement, and recognition), and using this information to devise a matched combination of enhancement (e.g. by magnification ⁄enlargement of educational material), training, and circumvention. Children with cerebral visual impairment tend to vary in their visual performance both during the day and from one day to another. Perceptual visual dysfunction is subject to fatigue so that if it is sought when the child is performing well, the deficiency may not be evident. Additional low intellectual ability can interfere with visual testing. On the other hand, parents and carers have an in-depth knowledge of their child’s day-to-day visual performance, and structured history taking provides an effective means of estimating visual function and allows helpful feedback on the parents’ observations. Questioning strategies designed to provide an estimate of visual function, like those described by Ferziger et al., provide a reproducible means of estimating vision and complementing objective measurement. They are particularly helpful in the context of severe impairment, and when seeing a child on a ‘bad day’. Structured history taking strategies have also been developed to seek specific visual disabilities, for which targeted solutions can be implemented. Question inventories can be employed in the form of a questionnaire for the purposes of validation; but thereafter, their use is enhanced by expert history taking, in which clarification is sought to fully characterize the visual difficulties and their impact. The sets of questions devised by Ferziger et al. and by McCulloch et al. to elicit information about the visual skills of children with severe cerebral visual impairment, potentially form the basis for the development of a standardized approach. The next move is to devise internationally agreed strategies to optimally compensate for each of the visual difficulties elicited.