Abstract

Background. Visual acuity (VA) and stereoacuity (SVA) are fundamental visual functions that decline with increasing retinal eccentricity. Patients with macular degeneration and other central vision disorders often rely on paracentral vision, yet location-specific reference data for VA and SVA across the parafoveal and perifoveal retina remain limited. This study aimed to quantify the distribution of binocular VA and SVA across eccentricity and meridian in young adults, develop prediction equations with 95% prediction intervals, and examine the relationship between these two visual functions in the paracentral retina.
Methods. Thirty-five healthy young adults (13 males, 22 females; mean age 27.23 ± 2.43 years) were recruited. Binocular VA and SVA were measured at 48 test positions across eight meridians (0°, 45°, 90°, 135°, 180°, 225°, 270°, 315°) and six eccentricities (2.5° to 15° in 2.5° increments) using a polarized 3D display system. A four-alternative forced-choice task was employed with tumbling E optotypes for VA and random-dot stereograms for SVA. Eye tracking ensured fixation stability throughout testing. Generalized estimating equations were used to analyze the effects of eccentricity and meridian. Linear mixed-effects models and Bayesian Tobit models were employed to develop prediction equations. Ten-fold cross-validation assessed model generalizability.
Results. Both VA and SVA significantly declined with increasing eccentricity (P<0.001). VA decreased from a median of 0.40 logMAR at 2.5° to 1.20 logMAR at 15.0°, at a rate of 0.057 logMAR per degree. SVA increased from 2.1 log arcsec at 2.5° to 2.9 log arcsec at 7.5°, declining approximately three times faster than VA (0.154 log arcsec per degree). Both functions showed significant meridional anisotropy (P<0.001), with the horizontal meridian demonstrating 0.058 logMAR better VA and 0.106 log arcsec better SVA compared to the vertical meridian. Despite parallel declines with eccentricity, no significant correlations were observed between VA and SVA at any test position within 7.5° eccentricity (P>0.05).
Conclusions. VA and SVA deteriorate with increasing eccentricity in the paracentral retina, with stereopsis declining approximately three times faster and demonstrating a more pronounced horizontal-over-vertical advantage. The absence of correlation between VA and SVA suggests distinct neural mechanisms underlying these functions. The prediction equations with 95% prediction intervals provide reference benchmarks for healthy young adults, facilitating clinical interpretation of patient measurements and enabling objective assessment of disease-related changes in paracentral visual function.