Visual acuities and dark-adapted thresholds of children with Bardet-Biedl syndrome

We studied the visual acuities and dark-adapted sensitivities of 12 children with Bardet-Biedl syndrome. All except one child, who was seen only once, were tested serially. In the first decade of life, all visual acuities were within 2 octaves of normal. All but two final visual acuities obtained from patients in their second and third decades were more than 2 octaves poorer than normal. Dark-adapted sensitivities of all patients were, or became, significantly less than normal even in those patients whose period of follow-up was limited to the first decade of life. Of the 11 patients measured serially, seven showed decreases in dark-adapted sensitivities of at least 0.5 log unit during the follow-up period, and the last measured sensitivities of all patients were at least 2 log units less than the normal mean.

Optokinetic nystagmus thresholds of dark-adapted RCS rats

The thresholds of dark adapted RCS rats and controls were estimated from optokinetic responses to blue stimuli, and compared to thresholds derived from b-wave stimulus/response functions. The rats were tested at ages 25, 30 and 35 days, a period during which the RCS degeneration is evolving and normal retinal development is proceeding. At all ages the OKN thresholds of control rats were lower than those of the RCS rats, but only by age 30 days did b-wave thresholds discriminate RCS from controls. As the RCS disease progressed b-wave thresholds increased, but OKN thresholds did not change significantly. The discrepancy between the OKN and b-wave results may be due largely to the smaller OKN stimulus field, which probably stimulates mainly the posterior retina where the RCS degeneration is most advanced.