Photopic ON- and OFF-responses in complete type of congenital stationary night blindness in relation to stimulus intensity.

The complete type of congenital stationary night blindness (complete CSNB) is a retinal disorder where the ON-response b-wave of the photopic electroretinogram is reduced, while the ON-response a-wave and OFF-response d-wave are preserved. These findings are related to ON-bipolar cell dysfunction, whereas the effects of myopia, which is usually associated with complete CSNB, have not been studied yet. The aim was to investigate ON-bipolar cell dysfunction in complete CSNB with variable-intensity stimuli, while excluding effects of myopia. ON- and OFF-responses were recorded from six complete CSNB patients, 10 control subjects (no refractive error; emmetropic control group) and 14 myopic subjects with similar refractive error and axial length as those with complete CSNB (myopic control group). Responses were elicited with stimulus intensities from 0.4 to 2.1 log cd s/m2 on a 20 cd/m2 background. Stimulus/response (S/R) functions were fitted to the Naka-Rushton equation and statistically evaluated. In complete CSNB, the S/R function of the a-wave measured at the time corresponding to the controls showed a lower Vmax than for the emmetropic controls, while all parameters were similar to the myopic control group. The b- and d-wave S/R functions of the complete CSNB group were similarly different to both control groups--for the b-wave, the Vmax and n were significantly lower, and for the d-wave, the sigma was significantly higher. These findings suggest that in complete CSNB, dysfunction of ON-bipolar cells influences the dynamics of the ON-response b-wave and OFF-response d-wave, independently of the effects of myopia.