Table 1 Baseline characteristics of the selected studies
Study | Publication year | Study design | Country | Sample size | Percent of male (%) | Mean age (years) | Number of cases | DR diagnosis | DR definition | Diabetes | Exposure Definition | Adjustment/matched | NOS score |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Young [28] | 1984 | Cohort | UK | 296 | 100.0 | 20.0–59.0 | 66 | Fundoscopic | Four Grades | Mixed | ≤10 measures/ week, > 10 measures/week | Crude | 6 |
Moss [29] | 1994 | Cohort | USA | 916 | NA | ≥ 21.0 | 238 | Fundus photographs | ETDRS | Mixed | Average loz/ day increase | Age, sex, HbA1c, retinopathy | 8 |
Kohner [30] | 1998 | Case control | UK | 2964 | 58.4 | 25.0–65.0 | 1102 | Retinal photography | ETDRS | T2DM | None, occasional, regular, heavy | Crude | 6 |
Rasmidatta [31] | 1998 | Case control | Thailand | 198 | NA | 60.5 | 63 | Fundoscopic examinations | Three grades | T2DM | Nondrinker, drinker, not regular drinker | HbA1c, cholesterol, triglyceride, HDL, BP | 6 |
Giuffrè [32] | 2004 | Case control | Italy | 132 | 38.6 | ≥ 40.0 | 45 | Fundus examination | ETDRS | Mixed | None, 1–19 years, 20 years or more | Crude | 6 |
Hirai [33] | 2007 | Cross-sectional | USA | 537 | 50.1 | 45.3 | 309 | Retinal photography | ETDRS | T1DM | Alcohol/No alcohol | Crude | 4 |
Beulens [34] | 2008 | Cross-sectional | Europe | 3250 | 29.7 | 15.0–60.0 | 304 | Retinal photographs | Three grades | T1DM | 0 g/week, 0.0–4.9 g/week, 5.0–29.9 g/ week, 30.0–69.9 g/week, 70.0–209.9 g/week, ≥210 g/week | Age, sex, centre, duration of illness, systolic BP, physical activity, smoking, BMI, presence of cardiovascular disease and HbA1c | 7 |
Xu [35] | 2009 | Cohort | China | 4141 | 43.4 | ≥ 40.0 | 366 | Fundus photographs | NA | General | Consumers, non-consumers | BMI, HDL, LDL, arterial hypertension | 7 |
Lee [36] | 2010 | Cohort | 14 countries | 1239 | 60.7 | 55.0–81.0 | 640 | Retinal photography | ETDRS | T2DM | 0, drinks /week 1–14, drinks/week > 14 drinks /week | Age, sex, HbA1c, systolic BP, duration of diabetes, BMI, cigarette smoking, ethnicity | 8 |
Yang [37] | 2013 | Cross-sectional | Korea | 978 | 54.1 | ≥ 19.0 | 112 | Fundus examination | ETDRS | Mixed | ≥4 alcoholic drinks/week, < 3 drinks/week | Age, gender, smoking status, regular exercise, BMI, serum total cholesterol, serum triglyceride, serum HDL cholesterol, anti-lipid drug use | 6 |
Jongsareejit [38] | 2013 | Cross-sectional | Thailand | 933 | NA | 59.5 | 214 | Indirect ophthalmoscope | International scales | T2DM | No, ever, current | Gender, age, diastolic BP, waist, total cholesterol, HDL, ccular perfusion pressure | 5 |
Harjutsalo [39] | 2014 | Cross-sectional | Finland | 3608 | 52.6 | 28.9–46.8 | 1191 | Retinal photography | NA | T1DM | Heavy drinker light drinker | Crude | 3 |
Fenwick [40] | 2015 | Cross-sectional | Australia | 395 | 64.1 | ≥ 18.0 | 235 | Fundus photography | ETDRS | T2DM | None, moderate, high | Education, income, language spoken at home, country of birth, lipid lowering drugs, hypertension drugs | 6 |
Tseng [41] | 2015 | Cohort | China | 573 | 61.8 | 58.9 | 91 | Funduscopic | Three grades | T2DM | Drinker, no-drinker | Crude | 6 |
MartÃn-Merino [42] | 2016 | Case control | UK | 17,130 | 55.9 | All stages | 7735 | Computerized records | NA | T2DM | 0–1 units/week 2–21 units/ week 22–34 units/week ≥35 units/week | Sex, age at index date, diabetes duration, primary care practitioner visits, referrals and hospitalizations, smoking, first HbA1c; systolic BP, glaucoma; cataracts, or lens extraction, HDL and triglycerides, and hypoglycaemic agents, including oral hypoglycaemic drugs and insulin | 7 |