On- and off-responses in photopic electroretinogram in complete and incomplete types of congenital stationary night blindness

The on- and off-responses of photopic electroretinogram (ERG) were recorded by rectangular light stimuli in 13 patients with complete type and 9 patients with incomplete type of congenital stationary night blindness. The positive on-response (b-wave) was significantly smaller in both types than in normal subjects (P < 0.001). The rapid off-response was normal in complete type patients, but was significantly smaller in incomplete type patients than in normal subjects (P < 0.001). Since the rapid off-response mainly reflects the decay of the late receptor potential of the cones, incomplete type patients may have a visual disturbance in the cone itself. Normal rapid off-response with abnormal on-response in complete type patients suggests the existence of a photopic visual disturbance in the middle retinal layer. These results strongly suggest that these two types of congenital stationary night blindness have a different pathogenesis in the photopic visual pathway.