To compare serum Lutein and Zeaxanthin (L/Z) concentrations between patients with nonproliferative diabetic retinopathy (NDR) and normal subjects, and to explore the effect of L/Z supplementation on serum L/Z level and visual function in NDR patientsSUBJECTS WERE DIVIDED INTO THREE GROUPS: 30 NDR patients supplied with Lutein 6mg/d and Zeaxanthin 0.5mg/d for three months (DR Group), 30 NDR patients without L/Z supplementation (DR Control Group) and 30 normal subjects (Control Group). Serum L/Z concentrations were measured by liquid high-resolution chromatography (HPLC). Visual acuity was recorded at baseline, 1 month, 2 months and 3 months post initial supplementation. Serum L/Z concentration were measured at baseline, 1 month and 2 months post initial supplementation. Contrast sensitivity (CS) and fovea thickness were recorded at baseline and 3 months post initial supplementation.Mean serum lutein concentrations in DR group were 0.0686±0.0296µg/mL and zeaxanthin concentration was 0.0137±0.0059µg/mL. The L/Z level of DR group was significantly lower compared to the control group (lutein: 0.2302±0.1308µg/mL, zeaxanthin: 0.0456±0.0266µg/m, P=0.000). The concentration of lutein and zeaxanthin in the DR control group at base line was 0.0714±0.0357µg/mL and 0.0119±0.0072µg/mL, respectively. There was no significant change of L/Z concentration in the DR control group during the study. Serum L/Z concentrations of DR group increased significantly after supplementation (F=109.124, P=0.000; F=219.207, P=0.000). Visual acuity improved significantly after medication. Compared with pre-medication, the average CS values of 1.5cpd, 3cpd and 6cpd after three months increased significantly (P=0.030,0.013,0.008) and the foveal thickness decreased. (P=0.05)Serum L/Z concentrations in DR patients are significantly lower than those in normal subjects, and L/Z intake can improve the visual acuity, CS and macular edema in DR patients, suggesting that L/Z supplementation might be targeted as potential potential therapeutic agents in treating NDR.