Prevalence of amblyopia and its determinants in a rural population: a population-based cross-sectional study

To determine the prevalence of amblyopia and its determinants in underserved rural villages of Iran. This population-based cross-sectional study was conducted in 3850 subjects selected from two underserved districts in the north (Kojur District, Nowshahr County, Mazandaran Province) and southwest (Shahyun District, Dezful County, Khuzestan Province) of Iran using multi-stage cluster sampling. The subjects underwent complete ophthalmic examinations including the measurement of uncorrected (UCVA) and best-corrected (BCVA) visual acuity, objective and subjective refraction, unilateral and alternate cover tests and ocular health examination. Amblyopia was defined as a reduction of BCVA to 20/30 or less in one eye or a 2-line interocular optotype acuity difference in the absence of any pathological factors. Of 3850 selected subjects, 3314 participated in the study (response rate = 86.08%). The mean age of the participants was 36.90 ± 20.21 years (range: 3-93 years). The prevalence and 95% confidence interval of total, bilateral, and unilateral amblyopia were 2.73% (2.17 to 3.38), 0.50% (0.28 to 0.83), and 2.23% (1.73 to 2.83), respectively. The most common type of amblyopia was anisometropic followed by strabismic and mixed. The lowest and highest prevalence was seen in the age group 6-20 years (1.36%; 0.65 to 2.49) and above 70 years (5.97%; 3.02 to 10.44), respectively. According to the results of multiple logistic regression analysis, compared to illiterate subjects, the odds ratio of amblyopia was 0.321 (P = .033) in subjects with High school education, 0.181 (P = .030) in subjects with secondary School education, and 0.486 (P = .041) in subjects with primary school education. The odds ratio of amblyopia for north villages residence vs southwest villages residence was 2.105 (P = .012). The odds ratio of amblyopia was 2.765 for age group>70 years vs. 6-20 years (P = .033). The prevalence of amblyopia was higher in north region, in participants with lower education level and older individuals. The high prevalence of amblyopia in older people may be due to the lack of screening programs in previous generations and consequently the lack of timely diagnosis and treatment.