<prompt> To define a health problem, prevalence of corneal xerosis should be -10.50.010.05  <response>: - corneal xerosis a serious problem in which cornea appears dull, dr and non wettable and eventually opaque. - To define a health problem, prevalence of corneal xerosis should be more than 0.01. Reference : Parks textbook of preventive and social medicine, 23rd edition, pg no:616 p 