Dark adaptation in pregnant and lactating Gambian women: feasibility of measurement and relation to vitamin A status.

The feasibility of dark adaptation measurement, using a Friedmann Visual Field Analyser, was assessed under field conditions in an isolated rural community in The Gambia, West Africa. It was found to be possible to obtain meaningful and reliable measurements on nearly all of the 117 subjects tested in two communities. Measurements were made throughout the cycle of pregnancy and in early lactation. No deterioration was observed in the later stages of pregnancy, in contrast to the deterioration reported previously in some vitamin A-deficient communities. Nearly all measurements were within the normal range quoted by the manufacturer. No evidence of improved adaptation was detected in women receiving a food supplement containing vitamin A. There were moderate variations with age of subject and with season, although the latter were not closely correlated with variations in vitamin A intake. Better nourished Gambian and Caucasian subjects showed slightly better performance than the village subjects, but this seems simply to reflect their better understanding of the test, since a small learning effect was observed. It is concluded that, despite limited comprehension of the nature of the test, reliable measurements could, with care, be obtained on illiterate adults from an unsophisticated society, and that in the marginally nourished community studied, a substantial increase in vitamin A intake had no discernible effect in improving dark adaptation performance.