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Vitamin A supplementation for retinitis pigmentosa.

We welcome the opportunity to address the comments of Drs Massof and Finkelstein 1 in their editorial that accompanies our article 2 in the June 1993 issue of theArchives. The editorialists inaccurately state that our conclusion was based on a single aspect of the cone electroretinogram (ERG). In fact, our conclusion regarding the beneficial effect of vitamin A supplementation for retinitis pigmentosa (RP) was based on two objective tests of retinal function—the 30-Hz (flicker) ERG and the 0.5-Hz (single flash) ERG. The 30-Hz ERG provides a measure of cone function, and the 0.5-Hz ERG, a measure of cone and rod function in combination. We reported that patients receiving 15 000 IU/d of vitamin A had a significantly slower rate of decline of remaining ERG amplitude on average than those not receiving this supplement, not only for 30-Hz responses ( P =.01) but also for 0.5-Hz responses ( P =.04). The editorialists