Abstract: Objective To investigate the associations of the contrast visual acuity in myopic eyes. Design Prospective non-controlled case series. Participants 123 right eyes of 123 subjects aged from 17 to 47 years-old with a spherical equivalent refraction (SE）varied from -0.5 D to -10.00 D were enrolled in this study. Methods MFVA-100 was used to measure contrast visual acuity. 100%, 25%, 10% and 5% contrast visual acuity under bright and dark backgrounds, and the pupil size for corresponding conditions were recorded. The relationship between contrast visual acuity and age, SE, pupil size under bright and dark backgrounds were analyzed. Multiple linear regression analysis was performed to determine the correlations between those variables. Main Outcome Measures Different contrast visual acuity, age, spherical equivalent, pupil size. Result At bright background, 100% contrast visual acuity was significantly correlated with spherical equivalent (t=2.551, P1=0.012, R2=0.043), but not with age and pupil size(all P>0.05); and contrast visual acuity (25%, 10%, 5%) was significantly associated with pupil size (t1=-4.111, P1<0.001, R21=0.123; t2=-4.434, P2<0.001, R22=0.14; t3=-5.766, P3<0.001, R23=0.216), but not with age (all P>0.05) and SE(all P>0.05). At dark background, 100%, 25% contrast visual acuity was significantly correlated with spherical equivalent (t1=2.695, P1=0.008, R21=0.057; t2=2.429, P2=0.017, R22=0.047), but not with age(all P>0.05) and pupil size(all P>0.05); and contrast visual acuity (10%, 5%) was significantly associated with pupil size (t1=-2.305, P1=0.023, R21=0.042; t2=-2.424, P2=0.017, R22=0.046), but not with age (all P>0.05) and SE (all P>0.05). Conclusion  100% contrast visual acuity was negatively correlated with SE under either bright or dark background, but no relationship with pupil size. While the 10%, 5% contrast visual acuity was negatively associated with pupil size. Under bright background, the effect of pupil size on visual acuity increased as the contrast reduced. The relationship between pupil size and 10%, 5% contrast visual acuities was less close under dark background than under bright background. （Ophthalmol CHN, 2012, 21: 319-322）　

Key words: myopia, contrast visual acuity, pupil size