Effect of vitamin A treatment on the prolongation of dark adaptation in Stargardt's dystrophy.

Abstract

Prolongation in recovery of rod thresholds has been demonstrated in Stargardt's dystrophy. One possible explanation for this finding includes an impairment of vitamin A transport by the retinal pigment epithelium (RPE). By delivering an increased amount of vitamin A to the RPE, it might be possible to overcome a relative deficiency of vitamin A utilization or transport, and thus improve rod dark adaptation. Baseline dark-adapted rod final thresholds were measured for five patients with Stargardt's dystrophy after 60 minutes of dark adaptation. A full dark-adaptation curve was then measured after exposure to a bleaching light for 5 minutes. Time of recovery to within 0.2 log units of the prebleach dark-adapted rod threshold was determined. Each subject then took a 14- to 18-day course of oral vitamin A, 50,000 IU daily. Dark adaptation was then reassessed using the same pretreatment protocol. Before treatment, all five patients had a prolongation of their rod recovery curve. There was no statistically significant difference between subjects in mean time taken to reach prebleach rod baseline thresholds before and after vitamin A treatment. These findings do not rule out the possibility that a delay in rod dark adaptation in Stargardt's dystrophy results from an inability to transport vitamin A from the RPE to photoreceptor cells. Nevertheless, a high dose of oral vitamin A taken for at least 14 days did not provide any objective improvement in dark-adaptation function in five such patients.