Prevalence and risk factors for anisometropia in the Tehran eye study, Iran

To determine the prevalence of anisometropia and its determinants in a population-based sample.

In a cross-sectional population-based study, stratified cluster sampling was carried out from the population of Tehran. Respondents were transferred to a clinic for an interview and ophthalmic examinations including tests for visual acuity with and without correction, cycloplegic refraction, the slit lamp examination, fundoscopy, and lensometry. Anisometropia was defined as unequal spherical equivalent cycloplegic refractions in the two eyes.

Of 4565 participants, cycloplegic refraction was performed in both eyes of 3519 people. The mean age of the examinees was 31.5 ± 18.0 (range, 5-86) years. The mean anisometropia was 0.34 diopter (D) (95% Confidence Interval (CI): 0.31-0.37). The prevalence rates of anisometropia more than 0.5, 1.0, 1.5 and 2.0 D were 18.5% (95% CI: 17.0-19.9), 6.7% (95% CI: 5.8-7.7), 3.8% (95% CI: 3.1-4.5) and 2.6% (95% CI: 2.1-3.1). The inter-gender difference in the prevalence of anisometropia ≥ 1.0D was not statistically significant (P = 0.952). The prevalence of anisometropia increased after the age of 45 years. Overall, 15.7% of the examinees had anisomyopia and 4.7% had anisohypermetropia equal to or more than 1.0D. Anisometropia was more prevalent among patients with cataracts, amblyopia, and pseudophakia. The prevalence rates of spherical and cylindrical anisometropia in the studied sample were 8.0% and 7.1%, respectively.

The prevalence of anisometropia in the population of Tehran is beyond negligible. It showed a significant increase with age. Results also indicate that myopic patients are more likely to have anisometropia.