The degree to which the normal eye can adapt to the dark is related to or dependent upon the eye's ability to regenerate visual purple. The relationship of vitamin A to the visual cycle has caused much development in improved methods of detecting vitamin A deficiency. For the most part these methods have been applied to adults and school age children. This study seeks to analyze this method as applied to pre-school age children.

Because of the paucity of evidence with regard to dark adaptation and the vitamin A status of pre-school children, this study is made. The purpose, therefore, is to add to the available data on this subject through an investigation of the bio-photometer as a means of detecting vitamin A deficiency in pre-school children.