No significant differences were observed among groups with respect to rates of decline of visual acuity. These results are summarized in Table 1. The mean declines in 30 Hz cone ERG amplitude from baseline for the higher amplitude cohort by year are plotted in Figure 1. The greatest separation among treatment groups occurred at years five and six. A intake averaged over all visits.
Vertical bars indicate SEs.
A intake lower than 2428 units, intermediate for those with intake between 2428 and 16,946, and least for those with intake of 16,947 units or greater. A significant difference was found among these groups by analysis of variance. Vitamin A intake greater than 18,380 units provided no greater benefit. These data support the hypothesis that a 15,000 unit supplement of vitamin A taken daily will slow the progression of the common forms of retinitis pigmentosa as monitored by ERG testing. The findings also suggest that a 400 unit supplement of vitamin E taken daily may have an adverse effect on the course of the common forms of this disease.