Sorsby's fundus dystrophy (SFD) is an autosomal dominant retinal degeneration caused by mutations in the tissue inhibitor of metalloproteinases-3 (TIMP3) gene. Mechanisms of the visual loss in SFD, however, remain unknown. In a SFD family with a novel TIMP3 point mutation, we tested a hypothesis that their night blindness is due to a chronic deprivation of vitamin A at the level of the photoreceptors caused by a thickened membrane barrier between the photoreceptor layer and its blood supply. Vitamin A at 50,000 IU/d was administered orally. Within a week, the night blindness disappeared in patients at early stages of disease. Nutritional night blindness is thus part of the pathophysiology of this genetic disease and vitamin A supplementation can lead to dramatic restoration of photoreceptor function.