We welcome the opportunity to address the comments of Drs Massof and Finkelstein1 in their editorial that accompanies our article2 in the June 1993 issue of the Archives.
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).
Berson EL, Rosner B, Sandberg MA, Hayes KC, Nicholson BW, Weigel-DiFranco C, Willett W. Vitamin A Supplementation for Retinitis Pigmentosa. Arch Ophthalmol. 1993;111(11):1456-1458. doi:10.1001/archopht.1993.01090110014001