Prevalence and causes of blindness in an urban area of Paraguay

PURPOSE: To determine the prevalence and causes of blindness in Piribebuy, Paraguay. METHODS: A population based study was conducted from September to November 2007 in Piribebuy, Paraguay. Based on the city map, seven clusters were randomly selected, containing 22 to 36 squares (423 to 578 houses) each, where all subjects &gt; 40 years old who agreed to participate were included in the study. Presenting vision acuity (VA) was obtained for each eye, with 'E' Snellen charts 6 meters far from the patient with appropriate light. Eyes with VA<20/60 were also tested with the pinhole. Objective and subjective refraction was performed, followed by examination of anterior segment under the slit-lamp, Goldmann applanation tonometry, and pupil dilatation with 0.5% tropicamide plus 0.5% phenylephrine, followed by evaluation of the posterior pole. Best corrected visual acuity was used to classify the patients as follows: blindness was defined as visual acuity of the better eye <20/400, low vision as 20/400 <VA <20/60 and visual impairment as VA <20/60. Similar to the methodology followed by the Rapid Assessment of Avoidable Blindness studies, in patients presenting more than one eye disease equally contributing to visual loss, only the most treatable or avoidable cause was recorded. RESULTS: 402 subjects received ophthalmological evaluation (92.2% of the original sample). Prevalence of blindness and low vision adjusted for gender and age was 1.0% (95% CI: 0.3-2.7) and 4.5% (95% CI: 2.8-7.1), respectively. Cataract was the only cause of blindness and the main cause of low vision (77.8% of the cases), followed by age-related macular degeneration (11.1%), pterygium (5.6%) and bilateral macular scar (5.6%). CONCLUSION: The prevalence of blindness in Piribebuy was 1% and the main cause was cataract.