Prevalence and risk factors for lens opacities in Nigeria: results of the national blindness and low vision survey.

PURPOSE: Investigate prevalence and risk factors for lens opacities among a nationally representative sample of Nigerians aged ≥ 40 years. METHODS: Across 305 clusters, 13,591 adults were examined. Every seventh participant (n = 1722) was sampled systematically and examined in detail, including lens opacity grading. Lenses were examined at the slit-lamp with pupil dilation and graded using the World Health Organization (WHO) system. Significant opacities were defined as nuclear, cortical, or posterior subcapsular opacity of WHO grade >1, or hyper/mature cataract. The category "Any Opacity" included hyper/mature opacity and aphakia/pseudophakia/couching. Data were collected on sociodemographic and environmental factors, including height and weight. RESULTS: A total of 1631/1722 (95%) in the normative subsample had their lenses graded. Prevalence of "Any Opacity" was 19.8% (95% confidence interval [CI]: 7.9-21.7) the prevalence of all types increased with age, and was higher in females and those not literate. Prevalence of nuclear, cortical, and posterior subcapsular were 8.8% (95% CI: 7.5-10.1); 11.7% (95% CI: 10.0-13.3); and 2.9% (95% CI: 2.1-3.8), respectively. In multivariate analysis, age was an independent risk factor for all types. Nuclear opacity was also associated with female sex (odds ratio [OR] 2.4; 95% CI: 1.5-3.6); lean body mass index (BMI; OR 2.0; 95% CI: 1.1-3.5); and the Igbo ethnic group (OR 4.4; 95% CI: 2.3-8.4). Cortical opacity was also associated with female sex (OR 2.1; 95% CI: 1.5-3.0) and the Yoruba (OR 0.45; 95% CI: 0.3-0.8), but not with BMI. "Other Lens Opacities," which includes couching, was significantly lower in the Guinea savannah region (OR 0.4; 95% CI: 0.2-0.9), while living in rain forest areas was protective for posterior subcapsular cataracts (OR 0.3; 95% CI: 0.1-0.7). CONCLUSIONS: A fifth of Nigerian adults have some degree of lens opacity. Further studies are needed to investigate the role of ethnicity, climate variables, and other risk factors.