To better shed light on these conflicting findings and to quantify the potential between-study heterogeneity and provide better ability to detect smaller effect sizes, we conducted a comprehensive meta-analysis on 40 published studies from 1994 to 2016 with 4252 diabetic retinopathy cases and 5916 controls relating the variant of the ACE I/D polymorphism to the risk of developing DR. This evidence concerns the gene ACE and diabetic retinopathy.