First Author: S.Nakano JAPAN
Co Author(s): T. Hiraoka Y. Hasegawa T. Oshika
Purpose:
To evaluate the effect of monocularly and binocularly induced astigmatism on visual acuity.
Setting:
Twelve normal volunteers (31.2 ± 5.2 [mean ± SD] years) with spherical equivalent refraction between 0 and 6.00 diopters (D), refractive astigmatism up to 0.75 D were enrolled.
Methods:
After correcting each refractive error by spectacles, against-the-rule (ATR) or with-the-rule (WTR) astigmatism was intentionally produced in both eyes in three steps ( +1.0, +2.0 and +3.0D), and near visual acuity (NVA) and distant visual acuity (DVA) were measured by using OPTEC Vision Tester 6500 (Stereo Optical Co, Inc.). The cylindrical addition of different powers (+1.0 ~ +3.0D) was compensated with spherical lenses so that the spherical equivalent refraction became zero in each eye. These cylindrical additions were monocularly induced (i.e.; no astigmatism in fellow eye), and the same examination was repeated. The order of cylindrical induction with different powers and axes was randomly determined.
Results:
The mean logMAR DVA and NVA in each condition were -0.03 and -0.16 for binocular WTR, -0.17 and -0.16 for monocular WTR,
-0.05 and -0.08 for binocular ATR, and -0.17 and -0.18 for monocular ATR astigmatism at 1D induction. At 2D induction, they were 0.24 and 0.07, -0.13 and -0.12, 0.25 and 0.11, -0.13 and -0.13, respectively. At 3D induction, they were 0.44 and 0.28, -0.13 and -0.09, 0.49 and 0.31, and -0.09 and 0.08, respectively. When compared between binocular and monocular astigmatic induction, DVA and NVA were significantly better in monocular astigmatic induction than in binocular induction at all powers (p < 0.05), except NVA in WTR 1D induction (p=0.84). When compared between ATR and WTR astigmatism, there were no significant differences in DVA in all conditions (p > 0.05). Similarly, there were no significant differences in NVA in all conditions (p > 0.05). Significant correlations were found between astigmatic power and DVA in all conditions (r = 0.34~0.91, p = 0.017~0.001). Similarly, significant correlations were found between astigmatic power and NVA in all conditions (r = 0.34~0.89, p = 0.017~0.001).
Conclusions:
Both binocular and monocular astigmatic induction degraded near and distant visual acuity, depending on astigmatic power. Although both near and distant visual acuities were worse in binocular astigmatic induction than in monocular induction, they were not affected by astigmatic axes such as WTR and ATR in normal eyes. FINANCIAL DISCLOSURE?: No
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