Prevalence of vitamin-A deficiency in a community is assessed as the following:

Prevalence criteria for determining the xerophthalmia problem: Criteria Prevalence in population at risk (6 months to 6 years) Nightblindness More than 1% Bitot's spots More than 0.5% Corneal xerosis/corneal ulceration/ keratomalacia More than 0.01% Corneal ulcer More than 0.05% Serum retinol (less than 10 mcg/dl) More than 5% Ref: Textbook of Preventive and Social Medicine by K Park, 19th edition, Page 486.