Study population

This study was carried out in Fengyutan Healthcare Centre which was part of a model for prevention of DR in Liaoning Diabetic Eye Centre. It is located in the Fengyutan Sub-District of Shenyang City in North China. There are more than 80 000 residents and five communities (Yutan, Yonghuan, Taoyuan, Qingnian and Zhongxin community) in Fengyutan Sub-District. Multistage, stratified random sampling was carried out on a selection of residents. First, the five communities were numbered, and then four were randomly selected from the five numbers. Second, the household health files registered in Fengyutan Healthcare Centre were numbered, and 400 households in each of the four selected communities were randomly chosen using a ‘true random number generator’ (https://www.random.org/). The participants had lived in Fengyutan for at least 2 years at the time the research was conducted. The selected households were informed by community officers using web page message or a telephone call. Finally, a total of 1400 subjects aged over 40 years attended from August 2013 to September 2014. After exclusion of patients with cancer, hepatic failure, renal failure, severe psychiatric disturbance or any other systemic medical condition (for example, severe cardiac or respiratory impairment) and subjects who would not attend voluntarily, 1163 (response rate 83.07%) eligible participants were enrolled.

Data collection

Information on name, gender, age, smoking and drinking habits, and health status (eg, duration of diabetes, hypertension duration, medical history and treatment methods) were obtained using a standardised questionnaire. In addition, participants were asked whether they had DM and if the diagnosis was made by a physician. All subjects were also asked to provide information on their current medication. Thus, known diabetes was defined according to self-reported physician diagnosis or the use of antidiabetic agents. Following an interview with a community office worker, all participants were asked to fast overnight (>8 h) before a physical examination. Waist circumference was measured at the level of the umbilicus in the standing position. Height and weight were measured without hats or heavy coats. Blood pressure (BP) was measured in the sitting position (first) and supine position (second), with a 5 min interval, using an upright standard sphygmomanometer. Subjects were asked to avoid vigorous physical activity and smoking for at least 30 min before BP measurement. The second BP measurement with fifth-phase diastolic pressure was used for analysis. All participants were subjected to stereo fundus photography to detect retinopathy by 45° through undilated pupils (non-mydriatic fundus camera; CR6-45NM; Canon, Tokyo, Japan). For each subject, two images for each eye centred on the fovea and optic disc were taken in a darkened room. Each image was graded in a blinded manner by two well-trained ophthalmologists separately for the presence of retinopathy lesions. If the grades were inconsistent, the other ophthalmologist would give the final diagnosis. The grade of retinopathy for each eye was determined; the individual classification was based on the worse eye. A clear retinal image could not be obtained for 41 subjects because of anterior segment opacity. Mydriasis with tropicamide 1% (Santen Pharmaceutical Co, Shiga, Japan) before 20 min of dark adaptation and binocular indirect ophthalmoscopy by two ophthalmologists who reviewed the retinal images was accepted.

The mayor and the welfare section of Fengyutan Sub-District approved this study. The research followed the tenets of the Declaration of Helsinki, and informed consent was obtained from the subjects after explanation of the nature and possible consequences of the study. The research was approved by the institutional ethics committee of The First Affiliated Hospital of China Medical University.

Laboratory methods

Blood was drawn from the antecubital vein for determination of high-density lipoprotein (HDL) cholesterol, triglycerides, fasting plasma glucose, and haemoglobin A1c in the morning after an 8 h fast. The 75 g oral glucose tolerance test was then carried out; 2 h later blood was drawn again. All biochemical analyses (enzymatic assay method) were performed at a commercial laboratory (The Endocrinology Laboratory, China Medical University, Shenyang, China).

Definition of MS, retinopathy, smoking, drinking and diabetes

The International Diabetes Federation 2005 (IDF) definition of MS describes a waist circumstance for a Chinese woman of ≥80 cm and a man of ≥90 cm plus two or more of the following four risk factors: (1) triglyceride concentration ≥1.70 mmol/L or specific treatment for this lipid abnormality; (2) HDL cholesterol <1.29 mmol/L or specific treatment for this lipid abnormality; (3) raised BP (systolic BP (SBP) ≥130 mm Hg or diastolic BP (DBP) ≥85 mm Hg) or treatment of previously diagnosed hypertension; and (4) fasting plasma glucose ≥5.6 mmol/L or previously diagnosed type 2 diabetes.10 Diabetes was diagnosed according to the 1999 WHO criteria.11 Stereoscopic colour fundus photographs were graded using the modified Airlie House classification and the Early Treatment Diabetic Retinopathy Study retinopathy severity scheme.12 ,13 For each eye, the maximum grade in any of the seven standard photographic fields was determined for each of the lesions and used in defining retinopathy levels. Drinking was defined as alcohol intake more than once a month over the past 12 months. Smoking was defined as having smoked 100 cigarettes in one’s lifetime and currently smoking cigarettes.

Statistical analysis

Mean±SD was used to express measurement data. In univariate analysis, a t test was applied for continuous variables and χ² test for nominal-scale data. Independent risk factors for retinopathy were analysed using multiple logistic regression with a stepwise approach. Data management and statistical analyses were performed using SPSS statistical software (V.16.0). p<0.05 was considered significant.