CLDN5 and diabetes mellitus: The expression levels of ZO-1, Occludin, and Claudin-5 in the retina were markedly down-regulated in the DM group compared with that in the NC group (ZO-1: 0.08 ± 0.08 vs. 0.89 ± 0.56, p < 0.05; Occludin: 0.28 ± 0.03 vs. 0.90 ± 0.30, p < 0.05; Claudin-5: 0.22 ± 0.08 vs. 0.87 ± 0.48, p < 0.05, respectively).