APOA2 and type 2 diabetes mellitus: apoE/apoC-II was negatively correlated with AI (r = −0.23, p < 0.001) and API (r = −0.18, p < 0.001), and apoC-III, apoE, apoB, apoC-II, apoB/apoA-I, apoC-II/apoC-III, and apoA-II/apoA-I were positively correlated with AI (p < 0.001) and API (p < 0.001), which indicated that they contributed to the occurrence of T2DM and severity of DR.