Effects of firsthand tobacco smoking on retinal vessel caliber: a systematic review and meta-analysis

Purpose To review the effects of firsthand tobacco smoking on central retinal arteriolar equivalent (CRAE) and central retinal venular equivalent (CRVE) of firsthand tobacco smokers. Methods We performed a search on EMBASE and PubMed for studies up to 15 th July 2022. Two independent reviewers selected studies with baseline data of CRAE and CRVE of current smokers, nonsmokers, and former smokers. Initial search identified 893 studies, of which 10 were included in the meta-analysis. Two independent reviewers extracted data from the included studies. The quality of studies was assessed by the Newcastle–Ottawa Scale. Results In this meta-analysis, 7431 nonsmokers, 2448 current smokers and 5786 former smokers, as well as 7404 nonsmokers, 2430 current smokers and 5763 former smokers were included in CRAE and CRVE analysis respectively. Nonsmokers had narrower CRVE (Weighted mean difference [WMD], -12.15; 95% CI, -17.33 – -6.96) and CRAE (WMD, -4.77; 95% CI, -7.96 – -1.57) than current smokers, and narrower CRVE (WMD, -3.08; 95% CI, -6.06 – -0.11) than former smokers. Current smokers had wider CRVE (WMD, 10.42; 95% CI, 7.80 – 13.04) and CRAE (WMD, 7.05; 95% CI, 6.65 – 7.46) than former smokers. Subgroup analysis and sensitivity analysis were performed. Conclusion Firsthand tobacco smoking resulted in wider CRAE and CRVE in current and former smokers, particularly in CRVE, and such changes may not be reversible after smoking cessation. Therefore, retinal vessel caliber may reflect the effects of firsthand tobacco smoking and be used to estimate the risk of cardiovascular diseases.