Normalization of binocular VERs after early onset visual deprivation in man

Visually evoked responses (VERs) were elicited by a reversing checkerboard target from a patient who suffered early onset bilateral deprivation of form vision as a result of a high refractive error, large amplitude strabismus, and congenital nystagmus. Monocular and binocular steady-state VERs were abnormal in amplitude and wave form even when a correction for the patient's large refractive error (compound hyperopic astigmatism) was worn. Although monocular VERs could not be normalized, a normal wave form and amplitude were restored to the binocular VER by the addition of horizontal prisms to the patient's ophthalmic prescription. The initially degraded binocular VER gradually acquired a normal morphology and amplitude as the magnitude of compensating base-out prisms in the patient's habitual ophthalmic prescription was systematically increased. The relationship between the binocular VER amplitude and the correcting prisms derived by the method described in this paper was subsequently used to arrive at a practical clinical solution for the patient's unusual and debilitating visual symptoms. This electrophysiological evaluation of binocular function at the cortical level proved to be a very useful diagnostic procedure with prognostic value; standard clinic procedures were ineffective in elaborating the patient's sensory and oculomotor disorders. The theoretical and practical implications of managing patients with a history of early onset visual deprivation are discussed.