—To determine whether supplements of vitamin A or vitamin E alone or in combination affect the course of retinitis pigmentosa.
—Randomized, controlled, double-masked trial with 2×2 factorial design and duration of 4 to 6 years. Electroretinograms, visual field area, and visual acuity were measured annually.
—Clinical research facility.
—601 patients aged 18 through 49 years with retinitis pigmentosa meeting preset eligibility criteria. Ninety-five percent of the patients completed the study. There were no adverse reactions.
—Patients were assigned to one of four treatment groups receiving 15 000 IU/d of vitamin A, 15 000 IU/d of vitamin A plus 400 IU/d of vitamin E, trace amounts of both vitamins, or 400 IU/d of vitamin E.
Main Outcome Measure.
—Cone electroretinogram amplitude.
—The two groups receiving 15 000 IU/d of vitamin A had on average a slower rate of decline of retinal function than the two groups not receiving this dosage (P=.01). Among 354 patients with higher initial amplitudes, the two groups receiving 15 000 IU/d of vitamin A were 32% less likely to have a decline in amplitude of 50% or more from baseline in a given year than those not receiving this dosage (P=.01), while the two groups receiving 400 IU/d of vitamin E were 42% more likely to have a decline in amplitude of 50% or more from baseline than those not receiving this dosage (P=.03). While not statistically significant, similar trends were observed for rates of decline of visual field area. Visual acuity declined about 1 letter per year in all groups.
—These results support a beneficial effect of 15 000 IU/d of vitamin A and suggest an adverse effect of 400 IU/d of vitamin E on the course of retinitis pigmentosa.