Clinical Question: Does tight blood pressure control improve visual outcomes in patients with diabetes and hypertension?
Setting: Outpatient (any)
Study Design: Randomized controlled trial (double-blinded)
Synopsis: In this substudy of the landmark United Kingdom Prospective Diabetes Study, 1,148 patients with hypertension and diabetes were assigned randomly in a 2:1 ratio to tight or loose control of blood pressure, with target blood pressures of 150/85 mm Hg or 200/105 mm Hg, respectively. The loose control target pressure was changed to 185/105 mm Hg midway through the study. Patients in the active treatment group were further randomized to receive captopril or atenolol in standard dosages, increased until control was achieved, with furosemide, nifedipine, methyldopa, or prazosin added (in that order), if needed.
The degree of retinopathy was evaluated at enrollment and every three years thereafter. Allocation to groups was concealed, outcome assessment was blinded, and analysis was by intention to treat. Patients were followed for a median of 9.3 years. The average blood pressure in the tight control group was 144/82 mm Hg, and in the loose control group, it was 154/87 mm Hg. The mean glycohemoglobins were similar in these groups: 7.2 percent during the first four years of the study, and 8.2 to 8.3 percent for the final four years.
The tight control group had fewer micro-aneurysms after 4.5 years of follow-up (23.3 versus 33.5 percent in the loose control group; number needed to treat [NNT] = 10), fewer hard exudates, fewer cotton wool spots, less progression of retinopathy, and less need for photocoagulation. These are all disease-oriented end points and do not necessarily result in significant worsening of vision or visual loss.
The primary patient-oriented outcomes were blindness and reduction in visual acuity. Visual loss in one eye was less likely in the tight control group, occurring in 2.4 percent of patients compared with 3.1 percent in the loose control group (P = .046). This corresponds to an absolute increase in risk with loose control of approximately one per 1,000 patient-years of treatment. After nine years, a lower likelihood of deterioration in either eye was noted in the tight control group (20.5 versus 32.8 percent; NNT = eight). However, there was no significant difference in the reduction of vision as assessed by the better eye.
An interesting finding, not otherwise commented on in the manuscript, was that 36 patients in the tight control group required cataract extraction compared with 14 patients in the loose control group. Judging by the other differences, this difference almost certainly was statistically significant.
Bottom Line: Tight blood pressure control results in a small benefit in the prevention of blindness, with an NNT of 1,000 patients for one year. Tight control also is associated with a reduction in loss of visual acuity after nine years (but not with shorter durations of follow-up) and an apparent increase in the likelihood of cataract extraction. (Level of Evidence: 1b)