The EOG light rise was normal in each subject; in 2 affected subjects, the rises were particularly high (>370% in 4 eyes, with 3 being ≥400%). Pattern electroretinograms were recorded in all subjects (Figure 3A). In subject A IV/2, the P50 component was normal in the right eye, but significantly lower than the left. In subject A II/9 it was still recordable, although markedly reduced in amplitude, but her son, subject A III/2, showed only minimal residual PERG activity. In the remaining subjects, the PERG was extinguished. Scotopic ERGs, including the rod-specific response and the bright white–flash ERG, were normal in 6 of 7 members in family A (Figure 3 B-C). The oldest member, A I/1, aged 88 years, had a low rod ERG b-wave amplitude, but this was within normal limits for age. The rod ERG b-wave of his son, A II/1, was of borderline amplitude, but normal implicit time (Figure 3B). The photopic ERG showed decreased b-wave amplitude, with no increase in implicit time in 6 symptomatic subjects, but a normal response in the asymptomatic A IV/2 (Figure 3D). The 30-Hz flicker ERG was reduced in symptomatic subjects, but, however small, showed no shift in implicit time(Figure 3E). Both ON and OFF responses were reduced in 6 of 6 patients in whom the test was abnormal. No abnormality was present in the asymptomatic A IV/2 (Figure 3F). The findings in A II/11 differ in that the ON response was delayed, and the OFF response was markedly reduced.