Table 1.
Main findings of the case-control and cross-sectional studies.
| Visual impairment type | Outcome | Type of metric | No. of studies | Cases | Sample size | Effect size (95% CI) | P | I2 | Small study effect | Excess significance bias | Largest study significant | PI | Level of evidence |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Diseases | |||||||||||||
| Open-angle glaucoma | Diabetes | OR | 13 | 11,472 | 3,480,114 | 1.46 (1.27–1.68) | <0.001 | 70.8 | No | Yes | Yes | 0.76–1.67 | II |
| AMD | Chlamydia pneumoniae | OR | 7 | 758 | 1395 | 1.11 (0.78–1.57) | 0.570 | 40.3 | No | No | No | −0.89–0.26 | NS |
| Diabetes | OR | 11 | NA | 175,305 | 1.30 (1.13–1.49) | <0.001 | 73.3 | No | NA | Yes | −28.02–46.18 | III | |
| Early AMD | Chronic kidney disease | OR | 14 | NA | 299,374 | 1.44 (1.24–1.68) | <0.001 | 69.9 | No | NA | Yes | NA | IV |
| Glaucoma | Diabetes | RR | 29 | NA | NA | 1.48 (1.29–1.71) | <0.001 | 82.6 | No | NA | NA | 1.02–3.60 | IV |
| Obstructive sleep apnoea | OR | 18 | 651,335 | 9,179,644 | 1.48 (1.26–1.75) | <0.001 | 83.8 | Yes | Yes | No | 0.81–2.70 | IV | |
| Nonarthritic ischemic optic neuropathy | Obstructive sleep apnoea | OR | 13 | 905 | 1332 | 3.8 (2.36–6.13) | <0.001 | 49.7 | Yes | Yes | Yes | 0.88–1.77 | IV |
| Any cataract | Gout | OR | 20 | NA | 56,248 | 1.47 (1.29–1.68) | <0.001 | 0.0 | Yes | NA | No | 0.98–1.55 | III |
| Type 2 Diabetes | OR | 23 | NA | 66,718 | 1.64 (1.42–1.88) | <0.001 | 60.9 | Yes | NA | Yes | 0.86–4.54 | II | |
| Diabetic retinopathy (T1D) | Metabolic syndrome | OR | 13 | NA | 10,651 | 1.38 (0.99–1.91) | 0.060 | 71.4 | Yes | NA | No | −27.14–64.37 | NS |
| Diabetic retinopathy | Non-alcoholic fatty liver disease | OR | 9 | NA | 7170 | 0.94 (0.51–1.72) | 0.810 | 96.3 | Yes | NA | Yes | 0.10–8.79 | NS |
| Mental health/cognition | |||||||||||||
| Diabetic retinopathy | Depression | OR | 20 | 4912 | 16,553 | 1.43 (1.21–1.69) | <0.001 | 81.8 | Yes | Yes | Yes | 1.15–2.63 | III |
| Open-angle glaucoma | Migraine | RR | 11 | NA | 467,008 | 1.23 (1.11–1.36) | <0.001 | 42.2 | No | NA | Yes | 0.44–4.27 | III |
| AMD | Cognitive dysfunction - measured by MMSE | Standard mean difference | 5 | NA | 1566 | −0.32 (−0.51; −0.13) | 0.001 | 51.6 | No | NA | Yes | −12.22–19.76 | IV |
| Cognitive dysfunction - measured by TMT-A | Standard mean difference | 2 | NA | 435 | 0.32 (0.13–0.51) | 0.001 | 0.0 | NA | No | Yes | −3.24–0.96 | IV | |
| Cognitive dysfunction - measured by TMT-B | Standard mean difference | 2 | NA | 435 | 0.10 (−0.10–0.29) | 0.330 | 0.0 | NA | No | No | −1.85–0.69 | NS | |
| Wet-AMD | Cognitive dysfunction - measured by MMSE | Standard mean difference | 3 | NA | 543 | −0.58 (−0.78; −0.38) | <0.001 | 0.0 | No | NA | Yes | 0.51–33.81 | IV |
| Cognitive dysfunction - measured by TMT-A | Standard mean difference | 2 | NA | 435 | 0.76 (0.13–1.39) | 0.020 | 78.5 | NA | No | Yes | 0.53–1.50 | IV | |
| Cognitive dysfunction - measured by TMT-B | Standard mean difference | 2 | NA | 435 | 0.32 (−0.04–0.69) | 0.080 | 44.9 | NA | No | Yes | 0.94–2.85 | NS | |
| Dry-AMD | cognitive dysfunction - measured by MMSE | Standard mean difference | 3 | NA | 543 | −1.16 (−1.72; −0.60) | <0.001 | 44.2 | No | NA | No | 0.53–3.52 | IV |
| Cognitive dysfunction - measured by TMT-A | Standard mean difference | 2 | NA | 435 | 1.22 (−0.18–2.62) | 0.090 | 91.8 | NA | NA | Yes | 0.72–1.87 | NS | |
| Cognitive dysfunction - measured by TMT-B | Standard mean difference | 2 | NA | 435 | 0.22 (−0.16–0.61) | 0.250 | 0.0 | NA | NA | No | NA | NS | |
| Onchocerciasis | Epilepsy | RR | 9 | NA | 5293 | 1.47 (1.04–2.09) | 0.030 | 81.0 | Yes | NA | No | 0.90–1.08 | IV |
| Modifiable risk factors | |||||||||||||
| Diabetic Macular Oedema | Dyslipidaemia - overall CHL | Standard mean difference | 7 | NA | 1125 | 30.08 (21.15–39.02) | <0.001 | 99.7 | No | NA | Yes | 0.66–2.80 | III |
| Dyslipidaemia - LDL levels | Standard mean difference | 7 | NA | 1125 | 18.62 (5.73–31.51) | 0.008 | 99.9 | No | NA | No | 0.79–7.41 | IV | |
| Triglyceride levels | Standard mean difference | 7 | NA | 1125 | 24.82 (9.21–40.42) | 0.002 | 99.8 | No | NA | No | 0.77–2.64 | IV | |
| Dyslipidaemia - HDL levels | Standard mean difference | 7 | NA | 1125 | 2.24 (−0.18–4.67) | 0.070 | 99.9 | No | NA | No | 0.18–59.90 | NS | |
| Diabetic retinopathy (T2D) | Dyslipidaemia - LDL levels | Mean difference | 4 | NA | 3465 | 3.74 (0.13–7.35) | 0.040 | 19.7 | No | NA | No | −23.18–72.80 | IV |
| Dyslipidaemia - overall CHL levels | Mean difference | 6 | NA | 4032 | 3.77 (−2.45–9.99) | 0.240 | 41.0 | No | NA | No | −8.71–4.43 | NS | |
| Dyslipidaemia - HDL levels | Mean difference | 5 | NA | 3698 | −1.14 (−2.43–0.15) | 0.080 | 0.0 | No | NA | No | 0.81–2.44 | NS | |
| Triglyceride levels | Mean difference | 7 | NA | 4366 | 9.08 (−4.20–22.36) | 0.180 | 64.6 | No | NA | No | 0.71–1.96 | NS | |
| Blood pressure | OR | 6 | NA | 7408 | 1.37 (0.96–1.95) | 0.080 | 45.5 | No | NA | No | 1.28–1.70 | NS | |
| Diabetic Retinopathy | BMI - overweight | OR | 6 | NA | 23,830 | 0.89 (0.75–1.07) | 0.210 | 65.5 | No | NA | No | NA | NS |
| BMI - obese | OR | 6 | NA | 23,830 | 0.97 (0.73–1.30) | 0.860 | 72.6 | No | NA | No | 0.47–1.64 | NS | |
| Intraoperative floppy iris syndrome | Hypertension | OR | 2 | NA | 1399 | 2.2 (1.15–4.19) | 0.020 | 0 | NA | NA | Yes | 0.41–2.30 | IV |
| Diabetes | OR | 4 | NA | 3281 | 1.26 (0.71–2.21) | 0.430 | 0.0 | No | NA | No | NA | NS | |
| Open-angle glaucoma | Hypertension | OR | 17 | NA | 60,084 | 1.25 (1.09–1.43) | 0.001 | 29.3 | No | NA | No | −6.94–14.42 | III |
| Pregnancy related conditions | |||||||||||||
| Retinopathy of prematurity | Hyperglycaemia | OR | 7 | 323 | 1211 | 4.15 (2.08–8.28) | <0.001 | 65.4 | Yes | Yes | Yes | 1.28–4.15 | IV |
| Pre-eclampsia | OR | 7 | 4356 | 32,890 | 1.29 (0.81–2.05) | 0.280 | 84.5 | No | Yes | Yes | NA | NS | |
| Visual impairment | |||||||||||||
| Open-angle glaucoma | Myopia | OR | 11 | NA | 43,958 | 1.92 (1.54–2.38) | <0.001 | 53.0 | Yes | NA | Yes | 0.32–5.64 | II |
| Diabetic retinopathy | Myopia | OR | 7 | NA | 27,638 | 0.83 (0.66–1.04) | 0.100 | 36.7 | No | NA | No | 1.08–1.20 | NS |
PI prediction interval, AMD advanced macular degeneration, T2D Type 2 diabetes, T1D Type 1 diabetes, CHL cholesterol, LDL low-density lipoprotein, HDL high-density lipoprotein, BMI Body mass index, MMSE mini-mental state examination, TMT-A Trial making test part A, TMT-B Trial making test part B, OR Odds ratio, RR Risk ratio, NS Non-significant.