EPIDEMIOLOGY OF BLINDNESS AND VISUAL IMPAIRMENT IN THE KINGDOM OF TONGA

Data on the prevalence and causes of blindness and visual impairment i n Polynesians are not readily available nor are they population based. This survey was designed to obtain an accurate estimate of blindness and its causes in Tonga. A sample of 4056 persons, aged 20 years and o ver, was selected by stratified cluster sampling. Participants receive d a screening, visual acuity examination, and, if visually impaired, w ere referred for detailed ophthalmic examination to determine the caus e. The prevalence of bilateral blindness in the study population was 0 .47% and all affected were aged over 50 years. It is estimated that th e national prevalence of bilateral blindness, adjusted for the sample weight applied in the selection procedure, is 0.56% (95% confidence in terval 0-1.13). Monocular blindness was three times more frequent. Cat aract was responsible for 68.4% of bilateral and 30.3% of monocular bl indness. Risk factors for life time experience of cataract included ag e and diabetes (self-reported). Neither smoking nor the presence of pt erygium were independently associated with cataract. Increasing years of education were protective against cataract for women, but not men. Corneal opacity from infection or trauma, and diabetes were responsibl e for most of the remaining visual impairment. While these results do not represent a significant public health problem by world standards t hey do provide a basis for planning blindness prevention programmes in the region.