VISUAL-EVOKED POTENTIALS WITH CROSSED ASYMMETRY IN INCOMPLETE CONGENITAL STATIONARY NIGHT BLINDNESS

Purpose. To investigate a proposed postretinal defect in patients with the incomplete form of congenital stationary night blindness (CSNB2) and to compare visual evoked potential (VEP) results with those found in various forms of albinism. Methods. Visual evoked potentials were p erformed in 10 patients with a diagnosis of CSNB2, 10 subjects with al binism, and 17 normal subjects. Visual evoked potentials were elicited monocularly with diffuse flash stimulation. Scalp electrodes were pla ced over each hemisphere and referred to the forehead. Interhemispheri c bipolar recordings were derived, and the correlation coefficient (CC ) was calculated for various segments of the interhemispheric response s. Results, A crossed visual evoked potential asymmetry pattern could be demonstrated in 9 of 10 patients with CSNB2. All subjects with albi nism and none of the normal subjects showed the crossed asymmetry patt ern. Statistical comparison of the CC computed for various segments of the interhemispheric response shows that the pattern of inversion in CSNB2 is more prominent in the 25 to 100 msec range (median CC, -0.37) and in the 175 to 250 msec range (CC, -0.27). In subjects with albini sm, all segments show a negative CC (range, -0.46 to -0.60). In normal subjects, all segments are positively correlated (range, 0.36 to 0.66 ). Conclusions. Crossed visual evoked potential asymmetry was found in patients with CSNB2; therefore, excessive decussation, as demonstrate d by this testing procedure, should not be considered as pathognomonic for albinism.