Objective: To determine the relationship between tight blood pressure (BP) control and the different aspects of diabetic retinopathy in patients with type 2 diabetes mellitus (DM). Setting: Nineteen hospital- based clinics in England, Scotland, and Northern Ireland. Design: Outcome of retinopathy status assessed by 4- field retinal photography related to allocation within a randomized controlled trial comparing a tight BP control policy aiming for a BP less than 150/85 mm Hg with a less tight BP control policy aiming for a BP less than 180/105 mm Hg. Subjects: One thousand one hundred forty- eight hypertensive patients with type 2 DM were studied. These patients had type 2 DM for a mean duration of 2.6 years at the inception of the Hypertension in Diabetes Study, had a mean age of 56 years; and had a mean BP of 160/94 mm Hg. Seven hundred fifty- eight patients were allocated to a tight BP control policy with angiotensin- converting enzyme inhibitor or β - blockers as the main therapy; 390 were allocated to a less tight BP control policy. Main Outcome Measures: Deterioration of retinopathy (≥ 2- step change on a modified Early Treatment Diabetic Retinopathy Study [ETDRSAbstractfinal scale), together with end points (photocoagulation, vitreous hemorrhage, and cataract extraction) and analysis of specific lesions (microaneurysms, hard exudates, and cotton- wool spots). Visual acuity was assessed at 3- year intervals using ETDRS logarithm of the minimum angle of resolution charts. Blindness was monitored as an end point with the criterion of Snellen chart assessment at 6/60 or worse. Results: By 4.5 years after randomization, there was a highly significant difference in microaneurysm count with 23.3% in the tight BP control group and 33.5% in the less tight BP control group having 5 or more microaneurysms (relative risk [RRAbstract, 0.70; P=.003). The effect continued to 7.5 years (RR, 0.66; P < .001). Hard exudates increased from a prevalence of 11.2% to 18.3% at 7.5 years after randomization with fewer lesions found in the tight BP control group (RR, 0.53; P < .001). Cotton- wool spots increased in both groups but less so in the tight BP control group which had fewer cotton- wool spots at 7.5 years (RR, 0.53; P < .001). A 2- step or more deterioration on the ETDRS scale was significantly different at 4.5 years with fewer people in the tight BP control group progressing 2 steps or more (RR, 0.75; P=.02). Patients allocated to tight BP control were less likely to undergo photocoagulation (RR, 0.65; P=.03). This difference was driven by a difference in photocoagulation due to maculopathy (RR, 0.58; P=.02). The cumulative incidence of the end point of blindness (Snellen visual acuity, S6/60) in 1 eye was 18/758 for the tight BP control group compared with 12/390 for less tight BP control group. These equate to absolute risks of 3.1 to 4.1 per 1000 patient- years, respectively (P=.046; RR, 0.76; 99% confidence interval, 0.29- 1.99). There was no detectable difference in outcome between the 2 randomized therapies of angiotensin- converting enzyme inhibition and β - blockade. Conclusions: High BP is detrimental to each aspect of diabetic retinopathy; a tight BP control policy reduces the risk of clinical complications from diabetic eye disease.
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