Objective To analysis the effect of lens opacity on the measurement of retinal vessel oxygen saturation. Methods This was a cross sectional study. Forty four eyes of 44 patients with different degrees of lens opacity were enrolled. There were 23 males and 21 females. The patients aged from 48 to 84 years, with the mean age of (71.8±10.3) years. The mean best corrected visual acuity was 0.65±0.22. The mean intraocular pressure was (14.2±4.3) mmHg (1 mmHg=0.133 kPa). The mean equivalent spherical degree was (−0.05±2.10) D. The opitical quality analysis system was applied to measure intraocular objective scattering index (OSI) caused by lens opacity. According to the OSI, the opacity of lens was divided into four groups. Patients with OSI value ＜1.0 was grouped to level 1, which indicated that the lens were basically transparent; patients with OSI value between 1.0 and 3.0 was grouped to level 2, which indicated early cataract; patients with OSI value between 3.0 and 7.0 was grouped to level 3, which indicated progressive cataract; patients with OSI value ＞7.0 was grouped to level 4, which indicated the mature stage of cataract. The retinal oximeter Oxymap T1 was used to capture the fundus images under different wavelengths. Pearson correlation analysis was used to analyze the correlation between retinal oxygen saturation and age, intraocular pressure, equivalent spherical degree and OSI. One way ANOVA was used to analyze the difference of retinal oxygen saturation among groups. Results The mean retinal arterial oxygen saturation, venous oxygen saturation and arteriovenous difference was (90.70±6.46)%, (47.34±13.51)%, (43.36±10.09)%, respectively. The correlations of retinal arterial oxygen saturation, venous oxygen saturation and arteriovenous difference with age, intraocular pressure, equivalent spherical degree was not statistically significant (all P＞0.05). The retinal arterial oxygen saturation and venous oxygen saturation was negatively correlated with OSI (r=−0.462,−0.500; P=0.002, 0.001), the arteriovenous difference and OSI was positively correlated (r=0.373, P=0.013). According to lens opacity, there were 11 eyes in level 1, 9 eyes in level 2, 14 eyes in level 3, 10 eyes in level 4. There were significant differences of retinal artery and venous oxygen saturation among different lens opacity levels (F=5.340, 4.710; P=0.003, 0.007); meanwhile, the arteriovenous difference was not significantly different (F=2.048, P=0.123). The retinal arterial oxygen saturation and venous oxygen saturation was significantly lower in the level 4 lens opacity group than any other three groups (all P＜0.05), but there was no statistically significant difference among level 1 to level 3 lens opacity group. Conclusion The effect of lens opacity of level 1 to level 3 is limited on the measurement of retinal oxygen saturation, but level 4 lens opacity will cause decrease of retinal artery and venous oxygen saturation.