Astigmatic Blur in Partial Visual Field Exposure Induces Astigmatism Compensation in Developing Chick Eyes

To determine whether localized retinal exposure to astigmatic blur is sufficient to drive compensatory changes in refractive and corneal astigmatism in developing chick eyes.

One hundred and thirty-six chicks were randomly assigned to nine groups combining three visual field conditions (full, horizontal, or vertical) and three lens treatments: with-the-rule (WTR) astigmatism (+2.00/-4.00 × 90), against-the-rule (ATR) astigmatism (+2.00/-4.00 × 180), or control (plano lens). Objective refraction and A-scan ultrasonography were measured at baseline (post-hatch day 5) and after 7 days of lens treatment, at which time corneal topography was also assessed. Data were analyzed using interocular differences (treated right eye minus untreated left eye) with two-way ANOVA.

Exposure to astigmatic blur induced significant compensatory changes in both refractive and corneal astigmatism, regardless of visual field extent. WTR blur elicited greater compensatory astigmatism than ATR blur (mean difference = 1.20 ± 0.16 DC, P < 0.001), with both conditions showing significant compensation compared to controls (P < 0.001). Visual field condition had no significant effect on astigmatic compensation (P ≥ 0.19). In contrast, spherical ametropia development was influenced by visual field exposure, with partial-field conditions inducing mild myopic shifts and deeper anterior chambers compared to full-field exposure (P < 0.001).

Localized retinal exposure to astigmatic blur is sufficient to drive compensatory changes in both refractive and corneal astigmatism, indicating that local retinal mechanisms can independently guide astigmatism compensation. In contrast, spherical refractive development appears to be modulated by the extent of visual field exposure.