Ocular motor behaviour of monozygotic twins with tyrosinase negative oculocutaneous albinism

Abstract

The involuntary nystagmus movements of 16- year-old monozygotic twins with tyrosinase negative oculocutaneous albinism were examined. On primary gaze both girls exhibited bilateral conjugate horizontal nystagmus, a jerk with extended foveation waveform, and similar frequencies (2.0 Hz:19 Hz), although the fast phases were in opposite directions. The mean amplitudes differed markedly (6.8°:3.7°), as did the position of the null zones (+20° to +30°:-25° to -35°) and the widths of the neutral zones (-250 to +200:-250 to -350). Since the twins have identical genotypes these differences must have arisen from other sources.