Effect of axis orientation on visual performance in astigmatic eyes.

PURPOSE To determine the effect of axis orientation on visual performance in astigmatic eyes. SETTING Department of Ophthalmology, Kitasato University, Kanagawa, Japan. DESIGN Investigational simulation. METHODS Healthy volunteers with no ophthalmic disease other than refractive errors were enrolled. After cycloplegic refraction was fully corrected with a 3.0 mm artificial pupil, with-the-rule (WTR), against-the-rule (ATR), and oblique (OBL) astigmatism of 1.0 diopter (D), 2.0 D, and 3.0 D were produced using trial lenses in each subject. Distance visual acuity and reading performance with uncorrected astigmatism imposed by the trial lenses under cycloplegia were assessed. Reading performance was determined from reading acuity and maximum reading speed using the Japanese version of the Minnesota Low Vision Reading Test acuity charts. RESULTS Distance visual acuity and reading performance in the 38 volunteers decreased significantly with increasing astigmatism (P<.001, analysis of variance). Distance visual acuity, reading acuity, and maximum reading speed with uncorrected astigmatism were significantly affected by axis orientation at each diopter of astigmatism (P<.05, 1.0 D and 2.0 D; P<.001, 3.0 D). All parameters showed significantly better values in eyes with WTR or ATR astigmatism than in eyes with OBL astigmatism at each diopter (P<.05); there were no significant differences between eyes with WTR astigmatism and eyes with ATR astigmatism. CONCLUSIONS Eyes with OBL astigmatism had significantly lower visual performance than eyes with WTR or ATR astigmatism. Correcting the preexisting astigmatism to acquire excellent visual outcomes may be necessary, especially in eyes with OBL astigmatism. FINANCIAL DISCLOSURE No author has a financial or proprietary interest in any material or method mentioned.