Bi-directional Refractive Compensation for With-the-Rule and Against-the-Rule Astigmatism in Young Adults

Abstract

Purpose The purpose of this study was to investigate the short-term effect of imposing astigmatism on the refractive states of young adults. Methods Nineteen visually healthy low-astigmatic young adults (age = 20.94 ± 0.37 years; spherical-equivalent errors [M] = −1.47 ± 0.23 diopters [D]; cylindrical errors = −0.32 ± 0.05 D) were recruited. They were asked to wear a trial frame with treated and control lenses while watching a video for an hour. In three separate visits, the treated eye was exposed to one of three defocused conditions in random sequence: (1) with-the-rule (WTR) astigmatism = +3.00 DC × 180 degrees; (2) against-the-rule (ATR) astigmatism = +3.00 DC × 90 degrees; and (3) spherical defocus (SPH) = +3.00 DS. The control eye was fully corrected optically. Before and after watching the video, non-cycloplegic autorefraction was performed over the trial lenses. Refractive errors were decomposed into M, J0, and J45 astigmatism. Interocular differences in refractions (treated eye – control eye) were analyzed. Results After participants watched the video with monocular astigmatic defocus for an hour, the magnitude of the J0 astigmatism was significantly reduced by 0.25 ± 0.10 D in both WTR (from +1.53 ± 0.07 D to +1.28 ± 0.09 D) and 0.39 ± 0.15 D in ATR conditions (from −1.33 ± 0.06 D to −0.94 ± 0.18 D), suggesting an active compensation. In contrast, changes in J0 astigmatism were not significant in the SPH condition. No compensatory changes in J45 astigmatism or M were found under any conditions. Conclusions Watching a video for an hour with astigmatic defocus induced bidirectional, compensatory changes in astigmatic components, suggesting that refractive components of young adults are moldable to compensate for orientation-specific astigmatic blur over a short period.

Compensatory Interactions between Corneal and Internal Astigmatism despite Lifestyle Changes

“…The mechanism behind the interaction between corneal and internal astigmatism is still unclear. However, laboratory studies using human and animal models suggest that the eye can detect and compensate for perceived astigmatic blur, particularly when astigmatism is oriented in WTR and ATR directions [31][32][33][34]. These findings suggest a bias towards the cardinal orientations in the development of refractive astigmatism and warrant further investigation.…”