DARK ADAPTATION AND EXPERIMENTAL HUMAN VITAMIN A DEFICIENCY

Abstract

Measurements of the dark adaptation of 17 young [male][male] made before, during, and after their stay on a vit. A-deficient diet show that cone and rod visual functions are both affected by the diet. The cone thresholds rise less than the rod thresholds, but their behavior is approx. parallel. The best single criterion of these changes is the final rod threshold after 30 min. in the dark. When subjected to the deficient diet, most individuals (14 of 17) responded by an immediate and unmistakable rise in visual threshold which continued for the duration of the diet. The other 3 subjects required 22, 55 and 60 days respectively before giving a clear and continuous rise in threshold. None of the subjects showed any skin symptoms, and only the 2 most extremely affected individuals recorded a subjective awareness of their raised visual thresholds. Partial recovery of the visual threshold was accomplished in some individuals by single large doses of vit. A. The extent of the recoveries was variable. The recoveries were never complete and were always temporary. Permanent recovery from an A-deficient diet was slow, requiring wks. and mos. The fastest subject returned to normal in 6 wks.; the slowest maintained a high threshold for over 3 mos., but had recovered completely after a yr. Efforts to influence the visual responses during and after the A-deficient diet by supplementation with other vits. yielded only negative results.