RAPID ASSESSMENT OF PREVALENCE OF CATARACT BLINDNESS AT DISTRICT LEVEL

Aim. To find an optimal cluster size and number of clusters for a reas onable estimate of the prevalence of cataract blindness in people aged greater than or equal to 50 years in 19 rural districts of a state in India, Materials, Cluster sampling methodology was used in 19 rural d istricts of Karnataka State, India. In each district, 15 clusters were randomly selected and 90 people aged greater than or equal to 50 year s were examined in each cluster. As a result the visual acuity and len s status of a total of 22 218 people were assessed. Methods. For each district, the design effect for cluster size ranging from 20 to 90 was calculated and the optimal cluster size and the required number of cl usters to achieve an accuracy of 1% errors and 80% confidence was asse ssed, Results. The age and gender adjusted prevalence of cataract blin dness varied from 1.58% to 7.24%, which justifies district level surve ys. The design effect is nearly 1.5 for clusters of sizes 30 and 40. W ith an average prevalence of 4.93% with 1% error and 80% confidence le vel, the optimal number of clusters is 37 and 28 for a cluster size of 30 and 40 respectively and the average sample size for a district aro und 1100. Conclusions, Rapid assessments for cataract blindness in tho se aged greater than or equal to 50 years can be conducted at district level in India with existing resources and at affordable costs, These provide reliable data, essential for effective monitoring and plannin g. Other parameters, for instance, surgical coverage can also be asses sed. The availability of standardized software for data entry and anal ysis and strict adherence to survey procedures is essential.