Follow-up study of blindness attributed to cataract in Karnataka State, India

Presentation of the results of rapid assessments of bilateral cataract blindness in persons 50 years of age and older in 19 districts of Karnataka State, India.

A total of 21,950 persons 50 years of age and older in 19 out of 20 districts were examined. In each district, 15 clusters were randomly selected and in each cluster the visual acuity and lens status were assessed in 90 persons 50 years of age and older.

Systematic Random Cluster Sampling was used. Assuming a prevalence of at least 4.3% and a design effect of 1.5, the survey was designed to give an estimated prevalence with a sampling error of 20% or less at 80% confidence. Visual acuity was measured with a tumbling E chart at 6 meters distance with available correction. Lens status was assessed by distant direct ophthalmoscopy with undilated pupil under semi-dark conditions.

The average age and sex adjusted prevalence of cataract blindness was 4.93%, with a variation of 1.58% to 7.24% in different districts. The prevalence in females was higher than in males. Cataract Surgical Coverage, an indicator for coverage and service utilization, varied from 42% to 68% in different districts. On average, males had a higher coverage than females. Of all aphakic eyes in the sample, 26.4% could not see 6/60. Barriers to cataract surgery are linked to service providers.

Rapid assessments for cataract blindness in persons aged 50 years and older can be conducted at district level in India with existing resources and at affordable costs. The results suggest an increase in cataract blindness since the previous survey of 1986. The long-term visual outcome needs improvement. Change in barriers to cataract surgery requires a shift in health education strategy and messages. The large variation in prevalence justifies district-level surveys. A change in the sampling frame from 15 clusters of 90 to 28 x 40 or 37 x 30 will increase the precision.