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KMID : 1159320160180040497
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Korean Journal of Vision Science
2016 Volume.18 No. 4 p.497 ~ p.505
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The Effects of Pinhole on Decimal Visual Acuity, Spherical Equivalent Refractive Error, and Astigmatism
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Shin Hyung-Sup
Jang Jun-Kyu
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Abstract
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Purpose: While changing the pinhole size, the decimal visual acuity of subjects was measured. The effects of pinhole size on visual acuity, spherical equivalent refractive error, and astigmatism are studied.
Methods: 118 adult subjects participated in this study. The mean age of subjects was 22.7±5.9 years. The decimal visual acuity was measured as a function of pinhole size (0.5 ~ 3.0 mm) and refractive error. The decimal visual acuity according to the pupil size was calculated and compared with the measured visual acuity.
Results: When the pinhole size was reduced, the decimal visual acuity of high myopia (-6.96±0.83 D) and mild myopia (-4.30±0.83 D) was significantly increased. The visual acuity of low myopia (-1.63±0.64 D) showed a maximum at pinhole size 1.0 mm. The visual acuity of emmetropia (-0.11±0.37 D) and hypermetropia (1.88±1.63 D) was slightly reduced. If the pupil size is reduced, the longitudinal spherical aberration and the longitudinal chromatic aberration were gradually reduced and the effect of the depth of field on the visual acuity was constant, but the diffraction was largely increased. Therefore, the calculated decimal visual acuity of emmetropia decreased below pupil size 1.5 mm. Up to pupil size 1.0 mm, the calculated visual acuity of myopia increased linearly because the influence of spherical equivalent refractive error is larger than that of diffraction and aberration. The changes of the decimal visual acuity of myopic high astigmatism (C= -2.73±0.63 D) and myopic mild astigmatism (C= -1.93±0.39 D) were equal to that of the myopia of similar spherical equivalent refractive error. Also that of hyperopic astigmatism (C= 1.29±0.72 D) was equal to that of the hypermetropia of similar spherical equivalent refractive error.
Conclusions: While decreasing the pinhole size, the visual acuity of emmetropia and hypermetropia decreased slightly because the diffraction increases largely and the aberrations decrease. Effect of the depth of field on decimal visual acuity was constant regardless of the pinhole size. The visual acuity of myopia increased largely due to the influence of spherical equivalent refractive error. The astigmatism can not be decreased by the pinhole because the spherical equivalent refractive error affects mainly on the visual acuity.
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KEYWORD
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Decimal visual acuity, Pinhole size, Pupil size, Spherical equivalent refractive error, Astigmatism
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