Correlation of dark adaptation test results with serum vitamin A levels in diseased adults.

Dark adaptation, is a reliable and highly reproducible indicator of vitamin A nutritional status in terms of function. Abnormal dark adaptation occurs over a fairly wide range of serum vitamin A values; however, the lower limit of serum vitamin A which is related to normal ocular function has not been determined. We studied dark adaptation in 67 patients with a variety of hepatic and gastrointestinal diseases or with chronic alcoholism. We found that a serum vitamin A level greater than or equal to 40 micrograms % predicted normal dark adaptation 95% of the time, a serum vitamin A level greater than or equal to 30 micrograms predicted normal retinal function 68% of the time and a level greater than or equal to 20 micrograms % predicted normal function 27% of the time. Thus, in individual patients with serum vitamin A levels less than 40 micrograms % one can be sure of vitamin A sufficiency only if a normal dark adaptation response is elicited.