This cross-sectional study was performed at the Zhongshan Ophthalmic Centre, Sun Yat-sen University, China. The study was approved by the Institute's Ethics Committee, and performed according to the discipline of the tenets of the Helsinki Declaration. All participants signed a written informed consent before entering the study.
Participants were recruited from a community in the Yuexiu district, Guangzhou, China. Subjects meeting the following inclusion criteria were recruited: (1) patients with type 2 DM aged 30 to 80 years, (2) ocular treatment-naïve, (3) visual acuity of 0.1 or more and able to complete an eye examination, and (4) a spherical equivalent (SE) of −12 diopters (D) or less, astigmatism of 4D or less and AL of 30 mm or less. The SE was calculated as spherical degree plus half of cylinder degree (SE = spherical degree + cylinder degree × 1/2). The participants were excluded if any of the following conditions were true: (1) any history of serious systemic diseases such as uncontrolled hypertension, serious cardiovascular or cerebrovascular diseases (ischemic heart disease, stroke), malignant tumors or nephritis; (2) any history of surgery, such as coronary artery bypass grafting, thrombolysis therapy, or kidney transplantation; (3) the presence of cognitive impairment, mental illness, or being unable to complete questionnaires and examinations; (4) any ocular diseases other than DR, such as glaucoma, vitreous-macular diseases (vitreous hemorrhage and retinal detachment), and amblyopia; (5) any history of ocular surgical interventions, such as a history of retina laser treatments or intraocular injections, glaucoma surgery, cataract surgery, or laser myopia surgery; and (6) abnormal refractive media (moderate to severe cataract, corneal ulcer, pterygium, corneal turbidity), poor fixation, and other characteristics that result in a poor quality of the fundus or OCT images.