Evoked potential analysis of visual pathways in human albinism.

PURPOSE: To explore the abnormal crossing of the retinogeniculate pathways in human albinos with visual-evoked potentials (VEPs). METHODS: The authors studied the symmetry of the topographic distribution of pattern onset/offset VEPs over the posterior part of the scalp elicited by monocular stimulation of each eye in 31 consecutive patients with different types of albinism. RESULTS: Twenty-one patients had asymmetric responses, with the major amplitude recorded over the lateral part of the scalp contralaterally to the stimulated eye in 14 patients and ipsilaterally in 7 patients. In two patients, the responses had a symmetric topographic distribution. In eight patients, the amplitude was so low that studying the symmetry was not possible. CONCLUSIONS: These findings demonstrate a non-uniform pattern of asymmetry as a result of the miswiring of the visual pathways in human albinism. Moreover, the low amplitude of the VEP recorded in a consecutive series of patients shows the difficulty of the study of this phenomenon in a clinical setting.

Contrast sensitivity in patients with nuclear cataracts.

Spatial contrast sensitivity and lens density were measured in 30 subjects (18 patients with pure nuclear cataracts and 12 age-matched controls). Contrast sensitivity was assessed using two techniques: a conventional monitor method in which gratings were viewed through the cataract (overall spatial contrast sensitivity) and a laser interferometer method in which gratings were formed directly on the retina (interferometric spatial contrast sensitivity), thus reducing the effect of an opaque lens on grating contrast. The degree of lens nuclear opacity was measured by assessing the density of Zeiss Scheimpflug slit-lamp video camera images. A contrast sensitivity loss was found by using both methods; this reduction reached statistical significance only when monitor stimuli were used. There was a significant correlation between lens nuclear density and sensitivity loss at spatial frequencies from 4 to 16 cycles/degree (r = .56 to .79 and P less than .05 to less than .001). A correlation coefficient of .82 (P less than .001) characterized the relationship between visual acuity (log of the minimal angle of resolution) and lens density. Nuclear lens opacity significantly affects contrast sensitivity; pure nuclear cataracts produce spatial visual losses at intermediate and high spatial frequencies.