Quantifying the effect of intraocular pressure reduction on the occurrence of glaucoma.

Purpose: To estimate the effect of reducing intraocular pressure (IOP) on: (i) the incidence of primary open-angle glaucoma (POAG) in patients with ocular hypertension (OH), and (ii) the progression of glaucoma. Methods: A meta-analysis of relevant randomized controlled trials was conducted. A literature search was performed to identify trials with: a randomized comparison of IOP-lowering intervention versus placebo or no treatment; visual field loss or optic disc changes as outcome; and follow-up >6 months. A pooled relative risk (RR) was calculated by a random effects model. Risk reduction of glaucoma conversion per mmHg of IOP reduction was quantified in a meta-regression model. Results: We identified nine OH and one POAG trials. A meta-analysis of OH trials gives a pooled RR of 0.61 [95% confidence interval (CI) 0.45-0.83]. A meta-regression shows a decrease of the RR of glaucoma conversion by 14% with each mmHg extra IOP reduction (P = 0.045). No meta-analysis of POAG trials was performed because only one study has been identified. Conclusion: There is sufficient evidence that OH therapy reduces the risk of conversion to glaucoma. This risk reduction increases with greater IOP reduction.