ACE and diabetic retinopathy: In a stepwise regression analysis including as independent covariates sex, age, duration of diabetes, total cholesterol, triglycerides and HbA1c levels, diabetic retinopathy status and use of ACE inhibitors and antihypertensive drugs, only use of ACE inhibitors remained inversely correlated (r2 = 0.38, p<0.0001) and HbA1c levels positively correlated (r2 = 0.01, p = 0.03) with AOPP concentration (data not shown).