According to prevalence criteria for determining xerophthalmia problems given by WHO, following are true for an endemic area:

Ans. (d) Night blindness 1%Ref : K. Park 23rd ed. / 615, 641, 899Criteria and Prevalence for Determining Xerophthalmia Severity:CriteriaPrevalence at risk* Night blindness>1%* Bitot's spot>0.5%* Corneal xerosis/keratomalacia>0.01%* Corneal ulcer>0.05%* Serum retinol>5%* Refer to previous answer for WHO classification of Xerophthalmia