• Journal of Korean Ophthalmic Optics Society
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• v.19 no.1
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• pp.93-98
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• 2014

Purpose: We were aim to investigate individual difference of visual acuity (VA) decrease and the change of contrast threshold (CT) according to the level of optically induced retinal defocus. Methods: A total of 69 eyes were examined using consist of ten-graded decimal vision chart (Landolt's ring). After conducted full correction of subject's refractive error, a monocular VA and CT were measured according to sequential increase by 0.25 D each time. Results: VA gradually decreased according to the increase of retinal defocus level. Individual difference of VA decrease was range from 1.2 to 0.6 in retinal defocus induced by +0.25 D. When retinal defocus was induced as much as +0.50 D and +0.75 D, it was in the range of 1.0 to 0.3 and 0.9 to 0.1 respectively. With +1.00 D, some participants didn't even recognize the 0.1 in the chart. With +1.75 D, whole participant did not recognize the 0.1. Also, CT was gradually decreased with increase of the retinal defocus level. Conclusions: Examiners should consider individual difference in the decrease of VA according to the level of residual refractive error when determining final prescription of a patient.

• Journal of Korean Ophthalmic Optics Society
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• v.20 no.2
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• pp.157-165
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• 2015

Purpose: To evaluate changes in central and peripheral refraction along the horizontal visual fields in myopic corneal refractive surgery group compared with emmetropes. Methods: One hundred twenty eyes of 60 subjects ($23.56{\pm}2.54$ years, range: 20 to 29) who underwent myopic refractive surgery and 40 eyes of 20 emmetropes ($22.50{\pm}1.74$ years, range: 20 to 25) were enrolled. The central and peripheral refractions were measured along the horizontal meridianat $5^{\circ}$, $10^{\circ}$, $15^{\circ}$, $20^{\circ}$, $25^{\circ}$ in the nasal and temporal areas using an open-field autorefractor. For analysis of post-op group, the group was classified by pre-op spherical equivalents of < -6.00 D and ${\geq}-6.00D$ as two post-op groups. Results: Pre-op spherical equivalent was $-4.56{\pm}0.92D$ (rang: -2.50 to -5.58 D) in post-op group 1, and $-7.09{\pm}0.96D$ (rang: -6.00 to -9.00 D) in post-op group 2. Spherical equivalent (M) in the emmetropes ranged from $-0.20{\pm}0.22D$ at center to $-0.64{\pm}0.83D$ at $25^{\circ}$ in the temporal visual field and to $-0.20{\pm}0.67D$ at $25^{\circ}$ in the nasal visual field; M in post-op group 1 ranged from $-0.16{\pm}0.29D$ at center to $-5.29{\pm}1.82D$ at $25^{\circ}$ in the temporal visual field and to $-4.48{\pm}1.88D$ at $25^{\circ}$ in the nasal visual field; M in post-op group 2 ranged from $-0.20{\pm}0.32D$ at center to $-7.98{\pm}2.08D$ at $25^{\circ}$ in the temporal visual field and to $-7.90{\pm}2.26D$ at $25^{\circ}$ in the nasal visual field. Among the three groups, there was no significant difference in M at central visual field (p=0.600) and at $5^{\circ}$ in the temporal visual field (p=0.647), whereas, there was significant difference in M at paracentral and peripheral visual field (p=0.000). Conclusions: Emmetropes had relatively constant refractive errors throughout the central and peripheral visual field and showed myopic peripheral defocus along the horizontal visual field. On the other hand, in myopic corneal refractive surgery group, there were significant differences in refractive errors between the central and peripheral visual field compared with differences in the central and peripheral refraction patterns of emmetropes.