Rhodopsin and visual threshold in retinitis pigmentosa.

Rhodopsin kinetics and visual threshold were determined in three subjects with a dominant form of retinitis pigmentosa. The retinal areas studied showed varying loss of sensitivity, which correlated well with the reduction in the measured density of rhodopsin in the test region. Rhodopsin photosensitivity was normal, and there was no evidence that either rhodopsin or the cone pigments regenerated more rapidly than normal. The findings in these cases of retinitis pigmentosa, when compared with the threshold changes induced by vitamin A deficiency or photic bleaching, suggest that the disease produces an imbalance between disc removal and new disc formation, which results in a progressive shortening of the photoreceptor outer segments and, eventually, in their complete disappearance.