Effect of Vitamin A Deficiency upon Rate of Pupil Dilation During Dark Adaptation

Abstract

Wald has recently shown that there is a definite chemical relationship between visual purple in the retina and vitamin A. The visual processes of light and dark adaptation form a cycle, vitamin A being the breakdown product of visual purple, as well as the precursor. It is found mainly in the light adapted retina, and only a trace exists in the dark adapted one. The latter, however, contains relatively large amounts of visual purple. 1 , 2

Wald has further shown that bleached isolated retinas contain much more vitamin A than retinas from light adapted animals. He concludes from this that the visual purple system loses vitamin A and relies upon the diet for its replacement. These results form an excellent basis for the explanation of night blindness caused by vitamin A deficiency.

If the stimulation of the rods, in which the visual purple is contained, has anything to do with the pupillary reflex, the measuring of the rate of dark adaptation, determined by changes in pupil diameter, might form the basis for an objective test for the determination of night blindness.

The experimental work done thus far consists of the measuring of the rate of pupil dilation during dark adaptation, by a method previously described. 3 This, in brief, involved the constricting of the pupil by an intense stimulus light followed by the taking of a series of photographs in virtually complete darkness, by means of an infrared source of light. The rate of pupillary constriction was also determined in the latter parts of the experiments, using a method described in a later paper. 4

Nine rabbits, from 6 to 8 weeks of age, were placed on the vitamin A-free diet, consisting of rolled oats, 60 parts; dry skimmed milk, 30 parts; and dry brewer's yeast, 10 parts. A few drops of Viosterol were administered by mouth every week.