In industrialized nations diabetic retinopathy(DR) is the most frequent microvascular complication of type 2 diabetes mellitus and the leading cause of visual impairment and blindness in the working-age population. The well-accepted strategy for prevention and treatment of diabetic eye complications focused on confirmed diabetic retinopathy, diabetic macular edema, cataract, etc, and there was no definitive therapy for preclinical central visual acuity (CVA) impairment, mainly because of its unknown pathogenesis. In our previous population-based study, the prevalence rate of early CVA impairment was as high as 9.1%, and that obviously limits the effects of diabetic eye diseases prevention and early-stage treatment strategy. Of note, the choriocapillaris is the only route for metabolic exchange in the retina within the foveal avascular zone, it was speculated that early CVA impairment is related to diabetic choroidopathy (DC). Recent research shows that the decreased macular choriocapillaris vessel density (MCVD) in diabetic eye ,which indicating early ischemia, is already present before diabetic macular edema can be observed; we have observed subfoveal choroidal thickness (SFCT) decreased significantly in the early CVA impairment patients. However, up til now, there was no epidemiology report on early CVA impairment in Chinese diabetes population. In the present study, we plan to conduct a 10-year perspective cohort observation of 2217 Chinese type 2 diabetic residents without diabetic retinopathy, diabetic macular edema, cataract and other vision impairing diseases, trying to find out related physical and biochemical risk factors. The results will facilitate discriminating high risk groups of early CVA impairment in diabetic patients. In the same time, a quantitative relationship between SFCT change, MCVD change and CVA change will be established. This study will demonstrate the role of DC in the occurrence of preclinical CVA impairment, and provide important theoretic evidence of blocking agents which target on DC.

Inclusion Criteria:

• ≥18 years old;
• Diabetes mellitus (DM) was defined as either blood hemoglobin A1C≥6.5%, use of diabetic medication or a physician diagnosis of diabetes.

Exclusion Criteria:

• None;

Type 2 diabetes mellitus. Diabetes mellitus (DM) was defined as either blood hemoglobin A1C≥6.5%, use of diabetic medication or a physician diagnosis of diabetes.