EFFECT OF VITAMIN-A TREATMENT ON THE PROLONGATION OF DARK-ADAPTATION IN STARGARDTS DYSTROPHY

Background: Prolongation in recovery of rod thresholds has been demons trated in Stargardt's dystrophy. One possible explanation for this fin ding includes an impairment of vitamin A transport by the retinal pigm ent epithelium (RPE). By delivering an increased amount of vitamin A t o the RPE, it might be possible to overcome a relative deficiency of v itamin A utilization or transport, and thus improve rod dark adaptatio n. Methods: Baseline dark-adapted rod final thresholds were measured f or five patients with Stargardt's dystrophy after 60 minutes of dark a daptation. A full dark-adaptation curve was then measured after exposu re 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, 50,00 0 IU daily. Dark adaptation was then reassessed using the same pretrea tment protocol. Results: Before treatment, all five patients had a pro longation of their rod recovery curve. There was no statistically sign ificant difference between subjects in mean time taken to reach preble ach rod baseline thresholds before and after vitamin A treatment. Conc lusions: These findings do not rule out the possibility that a delay i n rod dark adaptation in Stargardt's dystrophy results from an inabili ty to transport vitamin A from the RPE to photoreceptor cells. Neverth eless, a high dose of oral vitamin A taken for at least 14 days did no t provide any objective improvement in dark-adaptation function in fiv e such patients.