Astigmatism: Prevalence, Distribution and Determinants in Owerri, Nigeria

Abstract

Background: Astigmatism impairs focusing ability of the eyes at far and near distances. This causes distortion, blurred vision, eye strain, headache, makes difficult visual tasks such as reading, driving (especially at night), focusing on the classroom board and computer screen. This study determined the prevalence, distribution and determinants of astigmatism in Owerri, Imo State, Nigeria in order to establish a baseline data for the state. Materials and Methods: Three thousand, four hundred and fifty – one adults consisting of 2606 persons as test subjects and 845 persons as controls were randomly selected for the study. Structured – questionnaire was administered to the subjects and thereafter, the visual acuity at far and near including tonometry, ophthalmoscopy, perimetry, retinoscopy and subjective refraction were done. Astigmatic correction was prescribed in the minus cylinder format and astigmatism was defined as a cylindrical error less than -0.50 diopter cylinder in any axis. Astigmatism was classified by axis as with-the-rule (WTR), against-the-rule, and oblique astigmatism. Results: A prevalence of 20.9% and 22.5% of astigmatism was found in the study and control groups respectively. From the astigmatics, 59.4% and 61.1% of females in the study and control groups respectively (especially females aged 40-49) were mostly affected. WTR astigmatism of ≤1.00DC (P = 0.000) was statistically significant between study and control groups. A higher prevalence of astigmatism was found in subjects domiciled in the rural areas and caused by factors like environmental influences, poor nutrition and irrational first line drug use of chloroquine. Conclusion: To achieve the targets of vision 2020, we recommend periodic visual examination and health education on diet, drug use and safe environmental practises especially for people living in rural areas in low income economy like ours.