Medications or surgery for the treatment of open angle glaucoma

Open angle glaucoma (OAG) is the most common form of glaucoma and an important cause of blindness. Having a high intraocular pressure (IOP) is an important risk factor. Treatment for OAG aims to lower the IOP and thus reduce the risk of progressive loss of vision. IOP can be lowered by medications (eye drops), laser therapy or surgery. There are many different types of eye drops available and these are compared in a Cochrane review (Vass 2007). Surgery for glaucoma has also evolved in the last 40 years. The most common type is called trabeculectomy, or drainage surgery, that creates an opening at the wall of the eye to release fluid and reduce the IOP. Surgery may have complications during and after the operation and may fail in the long-term due to scarring. Drainage surgery forms a 'bleb' i.e. small blister like elevation on the surface of the eye which can sometimes be uncomfortable.

It is not clear whether medication or surgery is the better treatment for OAG. The purpose of this review was to review and assess evidence from randomised studies to compare treatment with medications with surgical treatments in terms of how well they work, their relative safety and cost-effectiveness. Four relevant trials were identified, treating 888 people. Three studies were in the UK and one in the US. These trials had been initiated over many years from 1968 up to the most recent trial in 1993. The earlier trials used medications, and in one trial surgical techniques that are now rarely used. Findings of these studies suggest that, in mild OAG, worsening of the condition was not different whether first treatment was medication or surgery, but surgery was associated with more eye discomfort at five years. In more severe glaucoma, surgery lowered IOP significantly more than medications (not widely used anymore) and reduced the risk of progressive loss of visual field. In three trials the risk of developing cataract was higher with surgery (trabeculectomy), although in one trial with follow-up beyond five years there was no difference in the number of cataract surgeries between treatment groups. There was insufficient evidence to determine how well more recently available medications work compared with surgery in more severe OAG, and which was the more cost-effective treatment option. More research is required.

Authors' conclusions: 

Primary surgery lowers IOP more than primary medication but is associated with more eye discomfort. One trial suggests that visual field restriction at five years is not significantly different whether initial treatment is medication or trabeculectomy. There is some evidence from two small trials in more severe OAG, that initial medication (pilocarpine, now rarely used as first line medication) is associated with more glaucoma progression than surgery. Beyond five years, there is no evidence of a difference in the need for cataract surgery according to initial treatment.

The clinical and cost-effectiveness of contemporary medication (prostaglandin analogues, alpha2-agonists and topical carbonic anhydrase inhibitors) compared with primary surgery is not known.

Further RCTs of current medical treatments compared with surgery are required, particularly for people with severe glaucoma and in black ethnic groups. Outcomes should include those reported by patients. Economic evaluations are required to inform treatment policy.

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Background: 

Open angle glaucoma (OAG) is a common cause of blindness.

Objectives: 

To assess the effects of medication compared with initial surgery in adults with OAG.

Search strategy: 

We searched CENTRAL (which contains the Cochrane Eyes and Vision Group Trials Register) (The Cochrane Library 2012, Issue 7), Ovid MEDLINE, Ovid MEDLINE In-Process and Other Non-Indexed Citations, Ovid MEDLINE Daily, Ovid OLDMEDLINE (January 1946 to August 2012), EMBASE (January 1980 to August 2012), Latin American and Caribbean Literature on Health Sciences (LILACS) (January 1982 to August 2012), Biosciences Information Service (BIOSIS) (January 1969 to August 2012), Cumulative Index to Nursing and Allied Health Literature (CINAHL) (January 1937 to August 2012), OpenGrey (System for Information on Grey Literature in Europe) (www.opengrey.eu/), Zetoc, the metaRegister of Controlled Trials (mRCT) (www.controlled-trials.com) and the WHO International Clinical Trials Registry Platform (ICTRP) (www.who.int/ictrp/search/en). We did not use any date or language restrictions in the electronic searches for trials. We last searched the electronic databases on 1 August 2012. The National Research Register (NRR) was last searched in 2007 after which the database was archived. We also checked the reference lists of articles and contacted researchers in the field.

Selection criteria: 

We included randomised controlled trials (RCTs) comparing medications with surgery in adults with OAG.

Data collection and analysis: 

Two authors independently assessed trial quality and extracted data. We contacted study authors for missing information.

Main results: 

Four trials involving 888 participants with previously untreated OAG were included. Surgery was Scheie's procedure in one trial and trabeculectomy in three trials. In three trials, primary medication was usually pilocarpine, in one trial it was a beta-blocker.

The most recent trial included participants with on average mild OAG. At five 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 (odds ratio (OR) 0.74, 95% confidence interval (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 five years than initial medication, (mean difference 0.74 dB (95% CI -0.00 to 1.48). Initial trabeculectomy was associated with lower average intraocular pressure (IOP) (mean difference 2.20 mmHg (95% CI 1.63 to 2.77) but more eye symptoms than medication (P = 0.0053). Beyond five years, visual acuity did not differ according to initial treatment (OR 1.48, 95% CI 0.58 to 3.81).

From three 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 (two trials) the risk of failure of the randomised treatment was greater with medication than trabeculectomy (OR 3.90, 95% CI 1.60 to 9.53; hazard ratio (HR) 7.27, 95% CI 2.23 to 25.71). Medications and surgery have evolved since these trials were undertaken.

In three trials 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 five 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).

Methodological weaknesses were identified in all the trials.

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