Assessment of vitamin A deficiency: The presence of any one of the criteria should be considered as evidence of a xerophthalmia problem in the community. - Criteria Prevalence in population at risk (6 months to 6 years) Night blindness more than 1 per cent Bitot's spots more than 0.5 per cent Corneal xerosis/ corneal ulceration/ keratomalacia more than 0.01 per cent Corneal ulcer more than 0.05 per cent Serum retinol (less than 10 mcg/dl) more than 5 per cent