A simple field test for identification of night-blindness.

A simple and replicable field test to measure dark adaptation time has been developed. It required a darkened room with a 5 watt bulb covered with a piece of black cloth, a spherical white object of 22 cm diameter suspended vertically from a horizontal string, a stool, a black curtain, a Maxwell electronic photographic flash unit and a stop-watch. The spherical object behind the closed curtain was hung 1.5 m away from the subject either to his left or right, or in the centre of the room. The seated subject was then exposed to 3 consecutive flashes, the curtain drawn, and the time taken to identify the position of the object was noted on the stop-watch. The test was conducted for 3 consecutive days on non-night blind young adult girls (n = 46) of the high income group (PC); underprivileged school-age children (n = 44) with a positive history of night-blindness (NB), and their age/sex pair-matched (n = 44) non-night-blind controls (NNB). The NB group had a significantly higher mean dark adaptation time as compared to the NNB and PC groups (14.9 sec vs 11.9 and 11.3 sec respectively). The mean serum vitamin A levels of NB, NNB and PC groups (15.8, 17.5 and 29.5 micrograms/dl respectively) were correlated with the dark adaptation times.