Abstract
PurposeTo determine the effects of astigmatism on contrast sensitivity (CS).MethodsEighteen normal volunteers (30.5 ± 6.0 [mean ± SD] years) were recruited. After correcting each refractive error by spectacles, against-the-rule (ATR) or with-the-rule (WTR) astigmatism of +1.00, +2.00 and +3.00 D was intentionally produced in both eyes, and then binocular CS was measured. The cylindrical addition of different powers (+1.00–+3.00 D) was compensated with spherical lenses so that the spherical equivalent refraction became zero in each eye. Subsequently, the above cylindrical addition was monocularly induced, and binocular CS was measured again. The relation between CS and astigmatic power, axis, and monocular or binocular astigmatism was investigated.ResultsWith binocular ATR and WTR astigmatism, increases in astigmatic power significantly correlated with decreases in the area under the log contrast sensitivity function (AULCSF). With monocular astigmatic defocus, astigmatic power addition did not affect AULCSF. With binocular astigmatic defocus of high-power (+2.00 and +3.00 D), ATR astigmatism deteriorated AULCSF more than WTR astigmatism. In a comparison between binocular and monocular astigmatic defocus, CS was significantly worse with binocular astigmatic defocus than with monocular astigmatic defocus at higher spatial frequencies regardless of astigmatic power.ConclusionsBinocular astigmatic defocus deteriorates CS depending on the amount of astigmatic power. ATR astigmatism reduces CS more than WTR astigmatism dose. In addition, binocular astigmatic defocus affects CS more severely than monocular astigmatic defocus especially at high spatial frequencies.
Highlights
With binocular ATR and WTR astigmatism, increases in astigmatic power significantly correlated with decreases in the area under the log contrast sensitivity function (AULCSF)
In a comparison between binocular and monocular astigmatic defocus, CS was significantly worse with binocular astigmatic defocus than with monocular astigmatic defocus at higher spatial frequencies regardless of astigmatic power
Binocular astigmatic defocus deteriorates CS depending on the amount of astigmatic power
Summary
It has been known that uncorrected monocular astigmatism deteriorates monocular visual acuity, contrast sensitivity (CS), reading performance and functional visual acuity [1,2,3,4,5,6]. About the effect of uncorrected astigmatism on binocular visual function in various conditions such as binocular, monocular, against-the-rule (ATR) or with-the-rule (WTR) astigmatism. Only limited studies have reported on the effect of monocular uncorrected astigmatism on binocular visual function [2,7,8]. Aniso-astigmatism was uncommon in the natural history [9,10,11]. Linke et al reported that 2.59% patients have 1.75 diopters (D) and more aniso-astigmatism in myopic refractive surgery candidates [10]. Some patients have residual binocular or monocular astigmatism after operation. It is crucial to clarify the influences of monocular or binocular uncorrected astigmatism on binocular CS
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