Normative Data for Non-Strabismic Binocular Vision Parameters in a Nepalese Young Adults

To establish population-specific normative data for non-strabismic binocular vision (NSBV) parameters in Nepalese young adults and to evaluate their association with age and gender.

This cross-sectional analytical study included asymptomatic adults aged 18-35 years who underwent comprehensive ophthalmic evaluation and standardized accommodative and binocular vision assessments. The mean and standard deviation were used to describe the central tendency and dispersion of the study parameters, respectively. Intergroup comparisons were performed using ANOVA and independent t-tests.

A total of 1,393 participants completed all NSBV assessments. The mean age of the participants was 25.04 ± 4.79 years. The mean values for key NSBV parameters were as follows: amplitude of accommodation, 8.75 ± 1.53 D; accommodative response (MEM), 0.50 ± 0.30 D; monocular accommodative facility, 9.98 ± 3.55 cpm; binocular accommodative facility, 6.39 ± 2.79 cpm; near point of convergence (break), 4.82 ± 1.50 cm; distance phoria, 0.19 ± 0.79 exophoria; near phoria, 2.96 ± 2.65 exophoria; and AC/A ratio, 2.61 ± 1.23. Amplitude of accommodation showed a strong negative association with age (AA = 16.20 - 0.30 × age; R² = 0.85; p < 0.001). Although gender differences were statistically significant for several parameters, the magnitude of these differences was small and not clinically meaningful.

This study provides the first large-scale normative clinical dataset of NSBV parameters in Nepalese young adults. Age significantly influences accommodative parameters, whereas gender-related differences are minimal. These population-specific normative values may support the screening, accurate diagnosis, and management of NSBVA and provide a contemporary reference for clinicians and researchers working with South Asian populations.