A new, simple, inexpensive means of testing functional vitamin A status: The night vision threshold test (NVTT). A preliminary field-test report

Vitamin A deficiency is the leading cause of preventable childhood blindnes s in developing countries, Each year, an estimated 13.5 million children wo rld-wide are unable to adapt to the dark and half a million children progre ss to complete blindness annually from lack of vitamin A. Most of the curre ntly available methods for assessing vitamin A status are expensive, requir e sophisticated instrumentation and are not efficacious in field conditions . A simple, inexpensive method was developed to identify children with defe ctive dark-adaptability, thereby providing a reflection of marginal vitamin A stores. The purpose of this preliminary study was to test the field-effi cacy of the Night Vision Threshold Tester (NVTT), Thirty-nine middle-school children with a mean age of 13.5 +/- 1.37 years were initially tested for their ability to adapt to the dark using the NVTT and were retested 3 weeks after vitamin A supplementation. A modified retinol dose response (MRDR) t est was also conducted before and after vitamin A supplementation. Among th ose who initially failed the NVTT test, 93 per cent (14/15) passed the test after supplementation. All of those who initially passed the NVTT test pas sed it upon subsequent testing. Those who failed the NVTT test had an odds ratio of 2.3 (95 per cent CI, 0.51-9.95) for having low vitamin A levels ac cording to the MRDR test but this did not reach statistical significance du e to the small sample size. The NVTT is a prime example of 'appropriate tec hnology' for developing nations as it has the potential to be used as a sur vey tool for assessing functional vitamin A status of individuals and commu nities with vitamin A deficiency. It would then be possible to target vitam in A distribution programs more judiciously, resulting in improved allocati on of scarce resources. Large-scale, double-blind placebo trials are needed to assess further the sensitivity and specificity of the NVTT.