A detailed history can help compensate for what may necessarily be a limited examination in these children. 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. 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 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.