Factors Affecting Visually Evoked Cortical Potentials such as Impaired Vision of Varying Etiology

¹ Ophthalmology and Psychology Services of the University of Florida, College of Medicine, Gainesville, Fla.

Visually evoked responses produced by flickering light stimulation were recorded from the scalp over the occiput in normal subjects and patients with unilateral central visual loss due to various causes. It was necessary to use a digital computer so that the small evoked signals could be detected from larger extraneous potentials not "time locked" to the stimulus. The signal to noise ratio was also enhanced by using a narrow band pass frequency filter. Intersubject comparisons of the evoked response obtained from central stimulation of one eye were limited by intersubject variability. However, there was much less variability in the evoked responses obtained from stimulation of each eye in the same subject. Impairment of vision in an eye with a central retinal lesion was indicated by a significant decrease in the size of the evoked response as compared to stimulation of the other normal eye and correlated roughly with the degree of visual loss. Uncorrected refractive errors and opacities of the media altered, the magnitude of the visual evoked response much less than lesions directly involving neural tissue. An apparent decrement in evoked cortical response size with increasing age was found. he potential for determining macular functioning and the integrity of central visual pathways even with media opacities were discussed.