Impact of vitamin A supplementation on xerophthalmia. A randomized controlled community trial

The value of biannual distribution of 200,000 IU of vitamin A in preventing xerophthalmia was assessed in a randomized, controlled community-based trial involving 25,000 preschool children in 450 villages of northern Sumatra. Results indicate that distribution was associated with a dramatic decline in xerophthalmia prevalence; that concurrent controls were critical for distinguishing spontaneous from program-related changes; and that the apparent level of benefit depended on the choice of clinical indicator(s). Night blindness ceases to be an accurate reflection of impact when prevalence rates are low, and comparison of Bitot's spot rates should be confined to new cases of disease.