Background: To elucidate whether eyelid squinting improves near and distance vision in against-the-rule (ATR) and with-the-rule (WTR) simple myopic astigmatism in pseudophakic eyes. Methods: A refraction-model eye was mounted on a wavefront analyzer. The eyelid fissure was simulated using a slit placed horizontally in front of the model eye. Four different refractive statuses [- 1.50 diopters (D) and - 3.00 D of both WTR and ATR simple myopic astigmatism] were set using cylindrical lenses. For each refractive status (emmetropia, - 1.50 D WTR, - 1.50 D ATR, - 3.00 D WTR, and - 3.00 D ATR astigmatism), wavefront aberrations were measured, both with and without the slit, 40 times each. Results: The 2 mm horizontal slit caused a hyperopic focus shift (+ 6.69 μm) in - 1.50 D WTR astigmatism, whereas, in - 1.50 D ATR astigmatism, it caused a myopic focus shift (- 2.01 μm). The astigmatism was decreased in the ATR astigmatism groups and increased in the emmetropia and WTR astigmatism groups, respectively. Total aberrations were decreased in the emmetropia and WTR astigmatism groups and increased in the ATR astigmatism groups. When the reference plane was set to the near plane, total aberrations were decreased in the ATR astigmatism groups. Conclusion: As the horizontal slit was placed in front of the model eye, the focus moves nearer in ATR astigmatism and farther in WTR astigmatism. These effects of eyelid cause improvement of near vision of pseudophakic eyes with ATR astigmatism.
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