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 blindness in developing countries. Each year, an estimated 13.5 million children world-wide are unable to adapt to the dark and half a million children progress to complete blindness annually from lack of vitamin A. Most of the currently available methods for assessing vitamin A status are expensive, require sophisticated instrumentation and are not efficacious in field conditions. A simple, inexpensive method was developed to identify children with defective dark-adaptability, thereby providing a reflection of marginal vitamin A stores. The purpose of this preliminary study was to test the field-efficacy 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) test was also conducted before and after vitamin A supplementation. Among those 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 passed 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 according to the MRDR test but this did not reach statistical significance due to the small sample size. The NVTT is a prime example of 'appropriate technology' for developing nations as it has the potential to be used as a survey tool for assessing functional vitamin A status of individuals and communities with vitamin A deficiency. It would then be possible to target vitamin A distribution programs more judiciously, resulting in improved allocation of scarce resources. Large-scale, double-blind placebo trials are needed to assess further the sensitivity and specificity of the NVTT.