A total of 792 patients with T2DM were enrolled and categorized into two groups: (1) the DR group consisted of 448 patients, which was further subclassified into a proliferative DR (PDR) group with 220 patients and a non-proliferative DR (NPDR) group with 228 patients; (2) the diabetes without retinopathy (DNR) group, comprised 344 patients who had no signs of DR. Single-nucleotide polymorphisms (SNPs), rs1800592 in the UCP1 gene, rs1801282, rs3856806 and rs1249719 in the PPARγ gene and rs11196205 in the TCF7L2 gene were genotyped in this study.