A Cochrane review [Abstract] 1 included 4 studies with a total of 888 participants with previously untreated open angle glaucoma (OAG). Surgery was Scheie's procedure in one study and trabeculectomy in 3 studies. In 3 studies, primary medication was usually pilocarpine, in 1 study it was a beta-blocker.
The most recent trial included participants with on average mild OAG. At 5 years, the risk of progressive visual field loss, based on a three unit change of a composite visual field score, was not significantly different according to initial medication or initial trabeculectomy (OR 0.74, 95% CI 0.54 to 1.01). In an analysis based on mean difference (MD) as a single index of visual field loss, the between treatment group difference in MD was -0.20 decibel (dB) (95% CI -1.31 to 0.91). For a subgroup with more severe glaucoma (MD -10 dB), findings from an exploratory analysis suggest that initial trabeculectomy was associated with marginally less visual field loss at 5 years than initial medication, (MD 0.74 dB, 95% CI -0.00 to 1.48). Initial trabeculectomy was associated with lower average intraocular pressure (IOP) (MD 2.20 mmHg, 95% CI 1.63 to 2.77) but more eye symptoms than medication (P = 0.0053). Beyond 5 years, visual acuity did not differ according to initial treatment (OR 1.48, 95% CI 0.58 to 3.81).
From 3 trials in more severe OAG, there is some evidence that medication was associated with more progressive visual field loss and 3 to 8 mmHg less IOP lowering than surgery. In the longer-term (2 studies) the risk of failure of the randomised treatment was greater with medication than trabeculectomy (OR 3.90, 95% CI 1.60 to 9.53; HR 7.27, 95% CI 2.23 to 25.71). Medications and surgery have evolved since these trials were undertaken.
In 3 studies the risk of developing cataract was higher with trabeculectomy (OR 2.69, 95% CI 1.64 to 4.42). Evidence from one trial suggests that, beyond 5 years, the risk of needing cataract surgery did not differ according to initial treatment policy (OR 0.63, 95% CI 0.15 to 2.62).
Comment: The quality of evidence is downgraded by study limitations (unclear blinding and high loss to follow-up in relation to observed absolute effect), by indirectness (differences between the interventions of interest and those studied), and by imprecise results (wide confidence intervals).
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