Review question
We reviewed the evidence about the effectiveness and safety of using devices modifying a standard surgery (trabeculectomy) for the treatment of glaucoma.
What is glaucoma and how is it treated?
Glaucoma is a disease of the optic nerve, which relays information from the eye to the brain to create images. Increasing pressure within the eye (increased intraocular pressure or IOP) damages the optic nerve leading to vision loss and blindness. It is the second leading cause of blindness worldwide in adults aged 50 years and over. Treatment for glaucoma aims to reduce pressure in the eye, which helps to slow down or prevent further vision loss. Eye pressure can be lowered with medicines, laser therapy, or surgery. Trabeculectomy is one of the most common standard surgical procedures for the treatment of glaucoma. It lowers IOP by creating a channel between the inside of the eye and the subconjunctival space (a fluid-filled space just under the surface of the eye), and it can be modified with implantable devices. Studies have reported using various devices such as the Ex-PRESS, the XEN Gel Stent, and the PreserFlo MicroShunt, along with materials such as Ologen, amniotic membrane, expanded polytetrafluoroethylene (ePTFE) membrane, Gelfilm, and others.
What did we do?
We searched medical databases for well-designed clinical studies in people with glaucoma comparing device-modified trabeculectomy techniques with standard trabeculectomy.
What did we find?
We found eight studies that met our inclusion criteria. These studies included 961 people with glaucoma and compared one of two types of device implanted during trabeculectomy versus standard trabeculectomy. Seven studies used the Ex-PRESS (434 participants), and one study used the PreserFlo MicroShunt (527 participants). These studies were conducted in North America, Europe, and Africa. Planned follow-up periods ranged from six months to five years. We found no studies using the XEN Gel Stent that met our criteria.
Main results
Five studies found that using the Ex-PRESS shunt during trabeculectomy may slightly reduce eye pressure by about 1.76 mmHg more than standard trabeculectomy. Another study showed that using the PreserFlo MicroShunt may be associated with a slightly higher eye pressure by 3.20 mmHg than standard trabeculectomy. Use of PreserFlo MicroShunt reduces the risk of developing abnormally low eye pressure by about 50% compared with standard trabeculectomy. Five studies found that the use of either device may lower the risk of subsequent cataract surgery (replacing a cloudy lens within the eye).
What are the limitations of the evidence?
The overall quality of the included studies varied by the type of device studied. Specifically, the quality was very low for studies using the Ex-PRESS, and low for studies using the PreserFlo MicroShunt study to flaws in study design and incomplete reporting. Therefore, the data need to be interpreted with caution.
How up to date is this evidence?
The evidence is current to 8 August 2021.
Use of an Ex-PRESS plus trabeculectomy may produce greater IOP reduction at one-year follow-up than standard trabeculectomy; however, due to potential biases and imprecision in effect estimates, the certainty of evidence is low. PreserFlo MicroShunt may be inferior to standard trabeculectomy in lowering IOP. However, PreserFlo MicroShunt may prevent postoperative hypotony and bleb leakage. Overall, device-modified trabeculectomy appears associated with a lower risk of cataract surgery within five years compared with standard trabeculectomy. 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 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).
Glaucoma is an optic neuropathy that leads to visual field defects and vision loss. It is the second leading cause of irreversible blindness in the world. Treatment for glaucoma aims to reduce intraocular pressure (IOP) to slow or prevent further vision loss. IOP can be lowered with medications, laser, or incisional surgery. Trabeculectomy is a surgical approach which lowers IOP by shunting aqueous humor to a subconjunctival bleb. Device-modified trabeculectomy techniques are intended to improve the durability and safety of this bleb-forming surgery. Trabeculectomy-modifying devices include the Ex-PRESS, the XEN Gel Stent, the PreserFlo MicroShunt, as well as antifibrotic materials such as Ologen, amniotic membrane, expanded polytetrafluoroethylene (ePTFE) membrane, Gelfilm and others. However, the comparative effectiveness and safety of these devices are uncertain.
To evaluate the benefits and harms of different devices as adjuncts to trabeculectomy on IOP control in eyes with glaucoma compared to standard trabeculectomy.
We used standard, extensive Cochrane search methods. The latest search was August 2021.
We included randomized controlled trials in participants with glaucoma comparing device-modified trabeculectomy techniques with standard trabeculectomy. We included studies that used antimetabolites in either or both treatment groups.
We used standard Cochrane methods. Our primary outcomes were 1. change in IOP and 2. mean postoperative IOP at one year. Our secondary outcomes were 3. mean change in IOP from baseline, 4. mean postoperative IOP at any time point, 5. mean best-corrected visual acuity (BCVA), 6. visual field change, 7. quality of life, 8. proportion of participants who are drop-free at one year, 9. mean number of IOP lowering medications at one year, and 10. proportion of participants with complications.
Eight studies met our inclusion criteria, of which seven were full-length journal articles and one was a conference abstract. The eight studies included 961 participants with glaucoma, and compared two types of devices implanted during trabeculectomy versus standard trabeculectomy. Seven studies (462 eyes, 434 participants) used the Ex-PRESS, and one study (527 eyes, 527 participants) used the PreserFlo MicroShunt. No studies using the XEN Gel Stent implantation met our criteria. The studies were conducted in North America, Europe, and Africa. Planned follow-up periods ranged from six months to five years. The studies were reported poorly, which limited our ability to judge risk of bias for many domains. None of the studies explicitly masked outcome assessment. We rated seven studies at high risk of detection bias.
Low-certainty of evidence from five studies showed that using the Ex-PRESS plus trabeculectomy compared with standard trabeculectomy may be associated with a slightly lower IOP at one year (mean difference (MD) −1.76 mmHg, 95% confidence interval (CI) −2.81 to −0.70; 213 eyes). Moderate-certainty of evidence from one study showed that using the PreserFlo MicroShunt may be associated with a slightly higher IOP than standard trabeculectomy at one year (MD 3.20 mmHg, 95% CI 2.29 to 4.11). Participants who received standard trabeculectomy may have a higher risk of hypotony compared with those who received device-modified trabeculectomy, but the evidence is uncertain (RR 0.73, 95% CI 0.46 to 1.17; I² = 38%; P = 0.14). In the subgroup of participants who received the PreserFlo MicroShunt, there was a lower risk of developing hypotony or shallow anterior chamber compared with those receiving standard trabeculectomy (RR 0.44, 95% CI 0.25 to 0.79; 526 eyes). Device-modified trabeculectomy may lead to less subsequent cataract surgery within one year (RR 0.46, 95% CI 0.27 to 0.80; I² = 0%).