<prompt> Prevalence of vitamin-A deficiency in a community is assessed as the following:Night blindness-10Corneal ulcer-0.1Bitot spots-0.5Decreased serum retinol level-0.05  <response>: Prevalence criteria for determining the xerophthalmia problem: Criteria Prevalence in population at risk 6 months to 6 years Nightblindness More than 1 Bitots spots More than 0.5 Corneal xerosiscorneal ulceration keratomalacia More than 0.01 Corneal ulcer More than 0.05 Serum retinol less than 10 mcgdl More than 5 Ref: Textbook of Preventive and Social Medicine by K Park, 19th edition, Page 486. 