In their recent report, Berson et al1 conclude that vitamin A has a beneficial effect and that vitamin E has an adverse effect on RP. On critical reading of the data, however, these conclusions may be less warranted than is intimated in the text. Several members of the Data Safety and Monitoring Committee (myself included) have had reservations about the interpretation of the findings.
The study was planned to include 600 patients to obtain sufficient statistical power to draw conclusions, but because of slow recruitment, 596 patients were followed up for 4 years, 472 were followed up for 5 years, and only 261 were followed up for 6 years. The 6-year data represent the first group of patients recruited and a "leading edge" of the dataset as patients accumulated at each year of follow-up. A glance at Figure 51(p768) shows that the positive effects of vitamin A and
Michael F. Marmor. A Randomized Trial of Vitamin A and Vitamin E Supplementation for Retinitis Pigmentosa. Arch Ophthalmol. 1993;111(11):1460–1461. doi:10.1001/archopht.1993.01090110018004