Scotopic threshold response in complete and incomplete types of congenital stationary night blindness

To study function of the rod visual pathway in eyes with complete and incomplete types of congenital stationary night blindness (CSNB), with special reference to the scotopic threshold response (STR) of electroretinograms (ERGs). ERGs were recorded from two patients with complete CSNB, four patients with incomplete CSNB, and four normal subjects. Full-field stimuli were used, with light intensities ranging from near absolute threshold to bright. Neither the rod b-wave nor the STR could be recorded from patients with complete CSNB. In contrast, a clear STR was recorded from patients with incomplete CSNB, although the absolute threshold of the response was elevated in proportion to elevation in the psychophysical absolute threshold. The b-wave stimulus threshold was not elevated, and the b-wave amplitude near threshold was normal in those with partial CSNB. STR latency was increased by approximately 80 msec in these patients, but b-wave latency was normal. Differences in the STRs of those with complete versus incomplete CSNB indicate that the rod system abnormality that characterized complete CSNB in different from the abnormality in incomplete CSNB. Furthermore, the greatly increased latency of the STR peak in patients with incomplete CSNB led to an abnormal relationship between the b-wave and the STR in these patients.