[Suppressive rod-cone interaction in complete and incomplete congenital stationary night blindness]

Dark-adapted rods have a suppressive effect on cone response (suppressive rod-cone interaction: SRCI). This phenomenon has been applied to analyze the pathological mechanism of congenital stationary night blindness (CSNB), but the results have been discrepant among the investigators. Alexander et al reported that 2 individuals with CSNB exhibited a normal SRCI, but Arden and Hogg reported an absence of SRCI in 4 cases of CSNB. We evaluated SRCI in complete and incomplete CSNB. SRCI was tested by measuring luminance threshold for flicker detection (685nm, 1.7 degrees in diameter, 20Hz) across the horizontal meridian of the visual field without and with full-field background illumination. In twelve normal subjects, a reduction of the flicker threshold was observed during presentation of the background. Five cases with complete CSNB showed normal SRCI, but in one case we failed to detect SRCI except at one tested locus. Similarly 5 cases of incomplete CSNB showed normal SRCI, but in one case we failed to detect SRCI except at one tested locus. These results may indicate that SRCI is normal in both complete and incomplete CSNB, but in some cases, SRCI is absent because of localized retinal dysfunction.