Impact of Correcting Anisometropia on Contrast Sensitivity Impairment in Myopic Patients

Abstract

Background: Myopic anisometropia disrupts binocular visual integration and may reduce contrast sensitivity, compromising functional vision even when high-contrast acuity is relatively preserved. Evidence comparing longitudinal contrast sensitivity outcomes after spectacle versus contact lens correction in non-amblyopic adults remains limited. Objective: To evaluate changes in monocular and binocular contrast sensitivity following correction of myopic anisometropia with spectacles versus contact lenses over three months. Methods: A single-blinded randomized controlled trial was conducted at Pakistan Vision Clinic, Lahore (January–June 2024). Fifty-four adults aged 18–35 years with myopia and anisometropia were randomized (1:1) to spectacle correction or soft contact lens correction. Contrast sensitivity was measured monocularly (OD, OS) and binocularly using the Pelli-Robson chart under standardized photopic conditions at 1 m at baseline, 1 month, and 3 months. Data were non-normally distributed (Shapiro–Wilk p<0.05). Within-group change was assessed using the Friedman test, and between-group comparisons at each time point used the Mann–Whitney U test with effect size r. Results: Both groups demonstrated significant improvement over time in OD, OS, and binocular contrast sensitivity (glasses: OD p=0.008, OS p=0.004, binocular p=0.016; contact lenses: OD p<0.001, OS p<0.001, binocular p<0.001). Median binocular contrast sensitivity increased from 1.75 to 1.95 log units with spectacles and from 1.75 to 2.00 log units with contact lenses at 3 months. Between-group differences were not significant at any time point (e.g., binocular at 3 months p=0.142; r=0.21). Conclusion: Correcting myopic anisometropia with either spectacles or contact lenses significantly improves monocular and binocular contrast sensitivity over three months, with no statistically significant difference between modalities.