Electrophysiological Investigation of the Visual Pathway in Human Albinos

Abstract

The general features of human albinism are reviewed. Further studies discussed show evidence for an increase in the number of contralaterally projecting optic nerve fibres in albino animals compared to their normally pigmented counterparts. A hypothesis is proposed that this misrouting should be reflected in scalp recorded visually evoked potentials in the form of contralateral hemispheric lateralisation on monocular stimulation in albino subjects but not in pigmented individuals. A total of twenty-six human albinos were examined using psychophysical and electrophysiological techniques. Reduced visual acuity and a high incidence of strabismus and nystagmus were evident. The visually evoked cortical potential (VECP) was recorded using different stimuli. Pattern reversal is shown to be unsuitable for evoking responses in albinos. The flash VECP, however, exhibits the predicted contralateral monocular lateralisation using reference recording. The major positive (P2) component shows a reduction in latency over the hemisphere contralateral to the eye stimulated in the albino group at a statistically significant level (p< 0.001); such a result was not found within a group of age and sex matched controls. Using a pattern appearance-disappearance stimulus contralateral monocular lateralisation is present in albinos but only in bipolar occipital recordings...