Rhodopsin and the electrical activity of the retina in congenital night blindness.

The inability of night-blind persons to see at low levels of illumination is usually attributed to a defect involving the biosynthesis of the visual pigment, rhodopsin. Accordingly, it has been assumed that the retinal rods of the congenital nyctalope are deficient in rhodopsin or its precursors. To test this hypothesis, fundus refiectometry was performed on two subjects, each having a different form of congenital night blindness (dominant and recessive, respectively). In both subjects, the concentration of rhodopsin and the rate at which it regenerated after bleaching were normal. Clearly, a photochemical basis for this anomaly is untenable. However, the electrophysiological responses of these subjects showed distinct abnormalities: (a) In the case of recessive inheritance, there was a normal light rise in the eye's standing potential, normal a-wave potentials in the ERG, but a very much reduced scotopic b-wave. (b) In the dominant form, the light rise in the standing potential was abnormal, and all ERG responses loere markedly depressed. These findings implicate the neural transmission pathways as the locus of disturbance in this anomaly. In view of a normal photochemistry, analysis of the restdts suggests that both the a-toave of the ERG and the light rise in the standing potential originate proximal to the outer segments of the receptors.