Device-modified trabeculectomy for glaucoma

Review Question

We reviewed the evidence about the effectiveness and safety of the use of devices in a standard glaucoma surgery (trabeculectomy) for the treatment of glaucoma.

Background

Glaucoma is a disease of the optic nerve that leads to vision loss and blindness. It is the second leading cause of worldwide blindness, and the blindness caused by glaucoma is permanent. Treatment for glaucoma aims to reduce pressure in the eye (IOP), which helps to slow down or prevent further vision loss from glaucoma. Eye pressure can be lowered with medications, laser therapy, or surgery. Trabeculectomy, the most common standard surgical procedure for the treatment of glaucoma, can be modified by using aids or devices during the surgery. Current studies have reported using various devices such as Ex-PRESS, Ologen, amniotic membrane, expanded polytetrafluoroethylene (E-PTFE) membrane, Gelfilm, gold shunt, T-flux, etc.

Study Characteristics

We found 33 studies that met our inclusion criteria. These studies included a total of 1542 glaucoma participants and compared five types of devices implanted during trabeculectomy versus trabeculectomy alone. Five studies reported the use of Ex-PRESS (386 participants), eight studies reported the use of Ologen (327 participants), 18 studies reported the use of amniotic membrane (726 participants), one study reported the use of E-PTFE (60 participants), and one study reported the use of Gelfilm (43 participants). These studies were conducted in North America, South America, Europe, Asia, and the Middle East. Planned participant follow-up periods ranged from three months to five years.

Key Results

Three studies found that the use of the Ex-PRESS shunt during trabeculectomy may slightly reduce eye pressure by about 1.6 mm Hg more than trabeculectomy alone. Another study did not find any difference in eye pressure at one year between trabeculectomy combined with Ex-PRESS versus trabeculectomy alone. Five studies did not find any important difference between trabeculectomy and Ologen compared to trabeculectomy alone. Nine studies found that the use of amniotic membrane during trabeculectomy may reduce IOP by about 4 mm Hg more than trabeculectomy alone at one-year follow-up. We did not find important differences for postoperative eye pressure at one year between trabeculectomy + E-PTFE and trabeculectomy alone. We did not find enough data regarding the evidence for the use of Gelfilm. It is uncertain whether these devices are as safe as trabeculectomy alone. The evidence is current to 22 December 2014.

Quality of the Evidence

The overall quality of the included studies varied by the type of device studied. Specifically, the quality was very low for Ex-PRESS studies, very low for Ologen studies, low for amniotic membrane studies, and unclear for other devices. Due to the various flaws in study design and incomplete reporting, the data need to be interpreted with caution, particularly for the amniotic membrane studies.

Authors' conclusions: 

Overall, the use of devices with standard trabeculectomy may help with greater IOP reduction at one-year follow-up than trabeculectomy alone; however, due to potential biases and imprecision in effect estimates, the quality of evidence is low. When we examined outcomes within subgroups based on the type of device used, our findings suggested that the use of an Ex-PRESS device or an amniotic membrane as an adjunct to trabeculectomy may be slightly more effective in reducing IOP at one year after surgery compared with trabeculectomy alone. The evidence that these devices are as safe as trabeculectomy alone is unclear. Due to various limitations in the design and conduct of the included studies, the applicability of this evidence synthesis to other populations or settings is uncertain. Further research is needed to determine the effectiveness and safety of other devices and in subgroup populations, such as people with different types of glaucoma, of various races and ethnicity, and with different lens types (e.g. phakic, pseudophakic).

Read the full abstract...
Background: 

Glaucoma is an optic neuropathy that leads to vision loss and blindness. It is the second most common cause of irreversible blindness worldwide. The main treatment for glaucoma aims to reduce intraocular pressure (IOP) in order to slow or prevent further vision loss. IOP can be lowered with medications, and laser or incisional surgeries. Trabeculectomy is the most common incisional surgical procedure to treat glaucoma. Device-modified trabeculectomy is intended to improve drainage of the aqueous humor to lower IOP. Trabeculectomy-modifying devices include Ex-PRESS, Ologen, amniotic membrane, expanded polytetrafluoroethylene (E-PTFE) membrane, Gelfilm and others. However, the effectiveness and safety of these devices are uncertain.

Objectives: 

To assess the relative effectiveness, primarily with respect to IOP control and safety, of the use of different devices as adjuncts to trabeculectomy compared with standard trabeculectomy in eyes with glaucoma.

Search strategy: 

We searched CENTRAL (which contains the Cochrane Eyes and Vision Trials Register) (2014, Issue 12), Ovid MEDLINE, Ovid MEDLINE In-Process and Other Non-Indexed Citations, Ovid MEDLINE Daily, Ovid OLDMEDLINE (January 1946 to December 2014), EMBASE (January 1980 to December 2014), PubMed (1948 to December 2014), Latin American and Caribbean Literature on Health Sciences (LILACS) (January 1982 to December 2014), the metaRegister of Controlled Trials (mRCT) (www.controlled-trials.com), ClinicalTrials.gov (www.clinicaltrials.gov), and the World Health Organization (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 search for trials. We last searched the electronic databases on 22 December 2014.

Selection criteria: 

We included randomized controlled trials comparing devices used during trabeculectomy with trabeculectomy alone. We also included studies where antimetabolites were used in either or both treatment groups.

Data collection and analysis: 

We used standard procedures expected by Cochrane.

Main results: 

We found 33 studies that met our inclusion criteria, of which 30 were published as full-length journal articles and three as conference abstracts. Only five studies have been registered. The 33 studies included a total of 1542 participants with glaucoma, and compared five types of devices implanted during trabeculectomy versus trabeculectomy alone. Five studies reported the use of Ex-PRESS (386 participants), eight studies reported the use of Ologen (327 participants), 18 studies reported the use of amniotic membrane (726 participants), one study reported the use of E-PTFE (60 participants), and one study reported the use of Gelfilm (43 participants). These studies were conducted in North America, South America, Europe, Asia, and the Middle East. Planned participant follow-up periods ranged from three months to five years. The studies were reported poorly which limited our ability to judge risk of bias for many domains. Only two studies explicitly masked outcome assessment so, we rated 31 studies at high risk of detection bias.

Low-quality evidence from three studies showed that use of Ex-PRESS compared with trabeculectomy alone may be associated with a slightly lower IOP at one year (mean difference (MD) -1.58 mm Hg, 95% confidence interval (CI) -2.74 to -0.42; 165 eyes). Cataract surgery and hyphema may be less frequent in the Ex-PRESS group than in the trabeculectomy-alone group (cataract surgery: risk ratio (RR) 0.32, 95% CI 0.14 to 0.74, 3 studies, low-quality evidence; hyphema: RR 0.33, 95% CI 0.12 to 0.94, 4 studies, low-quality evidence). The effect of whether Ex-PRESS prevents hypotony was uncertain (RR 0.92, 95% CI 0.63 to 1.33, 2 studies, very low-quality evidence). All these studies received funding from the device manufacturer.

Very low-quality evidence from five studies suggests that use of Ologen compared with trabeculectomy alone is associated with slightly higher IOP at one year (MD 1.40 mm Hg, 95% CI -0.57 to 3.38; 177 eyes). The effect of Ologen on preventing hypotony was uncertain (RR 0.75, 95% CI 0.47 to 1.19, 5 studies, very low-quality evidence). Differences between the two treatment groups for other reported complications also were inconclusive.

Low-quality evidence from nine studies suggests that use of amniotic membrane with trabeculectomy may be associated with lower IOP at one year compared with trabeculectomy alone (MD -3.92 mm Hg, 95% CI -5.41 to -2.42; 356 eyes). Low-quality evidence showed that use of amniotic membrane may prevent adverse events and complications, such as hypotony (RR 0.40, 95% CI 0.17 to 0.94, 5 studies, low-quality evidence).

The report from the only E-PTFE study (60 eyes) showed no important differences for postoperative IOP at one year (MD -0.44 mm Hg, 95% CI -1.76 to 0.88) between the trabeculectomy + E-PTFE versus the trabeculectomy-alone groups. Hypotony was the only postoperative complication observed less frequently in the E-PTFE group compared to the trabeculectomy-alone group (RR 0.29, 95% CI 0.11 to 0.77).

The one Gelfilm study reported uncertainty in the difference in IOP and complication rates between the two groups at one year; no further data were provided in the study report.

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