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Yumi Hasegawa, Takahiro Hiraoka, Tetsuro Oshika; Effects of Bilateral Astigmatic Defocus on Binocular Functional Visual Acuity. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):2960.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate the effects of bilateral astigmatism on binocular functional visual acuity (FVA).
Thirteen normal volunteers (mean age 29.1 ± 8.1 years) with spherical equivalent refraction between 0.00 and - 6.00 diopters (D) and refractive astigmatism up to 1.00 D were examined. After correcting each refractive error by spectacles, against-the-rule (ATR) astigmatism of +1.00, +2.00 and +3.00 D was intentionally produced in both eyes, and then binocular conventional visual acuity (CVA) and FVA were measured. With-the-rule (WTR) astigmatism of +3.00 D was also induced in both eyes, and binocular VA and FVA were measured. The same measurements were repeated with oblique (OBL) astigmatism of +3.00 D in both eyes. CVA was measured binocularly at 5 m using the Landolt chart, and FVA was evaluated binocularly using the FVA measurement system AS-28 (KOWA, Co. Ltd. Japan). In each measurement, cylindrical addition (+1.00 ~ +3.00 D) was compensated by spherical lenses so that the spherical equivalent refraction became emmetropic in each eye. The order of cylindrical induction with different powers and axes were randomly determined. We investigated CVA and FVA in relation to astigmatic power and axis.
Induction of ATR astigmatism from +1.00 to +3.00 D deteriorated both CVA and FVA according to the astigmatic power added (p < 0.0001, Spearman correlation test). With +2.00 D and +3.00 D ATR astigmatic defocus, FVA was significantly worse than CVA (p < 0.05, Wilcoxon signed-ranks test). The similar tendency was observed in +3.00 D WTR and OBL astigmatism, but not statistically significant (p = 0.15 for WTR, p = 0.06 for OBL). When compared among the axes of +3.00 D astigmatic defocus, FVA with OBL astigmatism was significantly worse than that with WTR astigmatism (p < 0.01, Fisher’s PLSD). In contrast, there were no significant differences in CVA among astigmatic axes.
Astigmatic defocus deteriorated FVA depending on the amount of astigmatic power. Astigmatic defocus affected FVA more severely than CVA. The influence of OBL astigmatism on FVA was larger than that of WTR astigmatism.
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