A systematic review including 3 RCTs in 6 publications with a total of 4 194 subjects was abstracted in DARE. Aspirin alone neither prevented the development of high-risk proliferative retinopathy (relative risk, RR=0.97, 95% confidence interval 0.85 to 1.11), nor increased the risk of vitreous haemorrhage (RR 1.0, 95% CI 0.8 to 1.3; 1 large study). There was no significant difference in the severity of vitreous or pre-retinal haemorrhage for aspirin versus placebo or aspirin-dipyridamole versus placebo. There was no statistically significant difference in the 5-year vitrectomy rates in the aspirin group compared with the placebo group (5.4% and 5.2%, respectively). There was no significant difference in the aspirin alone group and the aspirin-dipyridamole group in the development of microaneurysms. The mean annual increase in microaneurysms was significantly higher (P=0.02) in the placebo group than the treated group. In a two-period crossover study of 8 patients there was a mean aspirin-placebo treatment difference of 21% (95% CI 4 to 38, P=0.03).
Comment: The quality of evidence was downgraded by sparse data.