Retinitis pigmentosa

Retinitis pigmentosa is a collective name for a group of hereditary disorders involving degeneration of the retina, with progressive loss of vision, affecting about one in 3000 individuals worldwide. Patients typically develop night blindness in adolescence, followed by a loss of peripheral vision and eventually a loss of central vision in older adulthood. Both vitamin A and vitamin E have been. investigated as possible therapies in retinitis pigmentosa. Uncontrolled observations of patients who were treating themselves with these vitamins have suggested that supplementation might slow the progression of the disease.

This study, from the Massachusetts Eye and Ear Infirmary, Boston, was a randomized, controlled, double-masked trial of vitamin A and vitamin E supplementation in 601 patients with retinitis pigmentosa. The patient, aged 1849 years, were randomly assigned to receive 15,000 IU of vitamin A (as retinyl palmitate), 400 IU of vitamin E, both vitamins, or a placebo (containing trace levels of the vitamins) daily for four to six years. The principal outcome measure was cone electroretinogram amplitude, an objective measure of retinal function.

Patients receiving vitamin A (with or without vitamin E) showed a slower rate of decline in retinal function, as measured by cone electroretinogram amplitude, in comparison with those not receiving vitamin A. Vitamin E showed no effect in the group as a whole. However, in a subgroup of patients with initially better retinal function, those receiving vitamin E showed a faster rate of decline in retinal function than those not receiving the vitamin.

"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." The authors recommend that "most adult patients with the common forms of retinitis pigmentosa" should take a vitamin A supplement under medical supervision and that these patients should avoid the use of high-dose vitamin E supplements.

An accompanying editorial offers a different view. Although the editorial writers praise the design, execution, and analysis of the trial, they express caution about the investigators' conclusions and recommendations. Their principal concern is that the apparent beneficial effects involved electroretinogram measures only; there was no significant benefit for any measure of actual visual function. The editorial writers suggest several mechanisms by which vitamin A or vitamin E supplementation might influence cone electroretinogram amplitude without affecting vision. They also point out that there may be adverse effects associated with long-term vitamin A supplementation.

The editorial states, "We believe that the important observations of this study are strictly limited to the electroretinogram measures. Without a better understanding of the reason for the electroretinogram effects, we cannot conclude from the data that supplemental vitamin A alters the natural course of retinitis pigmentosa .... Given the somewhat speculative nature of the possible clinical benefits of vitamin A supplementation for retinitis pigmentosa, the potential risks of this therapy take on greater significance .... Our recommendation is to inform patients of the results of this study and of the potential risks of supplemental vitamin A and to caution them that the results of the study apply only to the electroretinogram and may not be generalizable to the loss of visual function."

Eliot L Berson et al, A Randomized Trial of Vitamin A and Vitamin E Supplementation for Retinitis Pigmentosa, Archives Opthalmology 111(6):761-772 (June 1993) [Reprints: Eliot L Berson, MD, Berman-Gund Laboratory, Massachusetts Eye and Ear Infirmary, 243 Charles Street, Boston MA 021141

Robert W Massof and Daniel Finkelstein, Supplemental Vitamin A Retards Loss of ERG Amplitude in Retinitis Pigmentosa [Editorial], Archives Opthalmology 111(6): 751- 754 (June 1993)

[Editor's note: This study also provides toxicity data on vitamin A: 15,000 IU taken on a daily basis for four to six years did not have any adverse effects.]

COPYRIGHT 1993 Frost & Sullivan
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