iStent for open-angle glaucoma

Citation: Le JT, Bicket AK, Wang L, Li T. Ab interno trabecular bypass surgery with iStent for open-angle glaucoma. Cochrane Database of Systematic Reviews 2019, Issue 3. Art. No.: CD012743. DOI: 10.1002/14651858.CD012743.pub2

What is the aim of this review?
The aim of this Cochrane Review was to find out whether the implantation of one or more iStent or iStent inject devices ('iStents'), compared with conventional medical, laser, or surgical treatments, can keep people who have primary open-angle glaucoma from needing to use glaucoma drops (i.e. keep them 'drop-free'). The glaucoma drops are used to control the fluid pressure within their eyes (called the intraocular pressure (IOP)). We also looked at average change from baseline in number of glaucoma drops needed to control IOP, average change from baseline (i.e. before treatment) in IOP, and health-related quality of life as defined by study investigators. We examined all outcomes at short-term (less than six months), medium-term (six to ≤ 18 months), long-term (> 18 months and ≤ 36 months) and greater than 36-month time points. We collected and analyzed all relevant randomized controlled trials (RCTs; clinical studies where people are randomly put into one of two or more treatment groups) to answer this question and found seven RCTs evaluating iStents.

Key messages
There was very low-quality evidence that treatment with iStents may have resulted in higher proportions of people who were drop-free at medium-term time points or who had better control of their IOP. None of the seven RCTs examined how the iStent affected quality of life and reporting on complications was highly variable. At present, clinical practice decisions should be based on provider judgment and patient preferences, given inconsistency in results and risk of bias in relevant studies published to date.

What was studied in the review?
Glaucoma is a group of eye diseases that cause irreversible damage to the optic nerve in the eye. If untreated, glaucoma can lead to blindness. Elevated IOP is the only known modifiable risk factor for open-angle glaucoma, which is the most common form of glaucoma. Conventional first-choice treatments for open-angle glaucoma include medical (e.g. glaucoma drops) or laser interventions. Surgery, which has a higher risk profile, is offered when glaucoma progresses despite treatment with medication or laser.

Minimally invasive glaucoma surgical procedures involve implantation of devices such as the iStent. They have been proposed as a safer alternative to standard glaucoma surgeries in people with mild-to-moderate forms of open-angle glaucoma. The iStent creates a 'bypass' between the front chambers of the eye and its natural drainage pathway. This bypass increases the flow of fluids out of the eye, which may decrease IOP and the need to use glaucoma drops to control IOP.

What were the main results of the review?
We identified four RCTs that randomized participants to treatment with iStents in combination with cataract surgery (called phacoemulsification) or with phacoemulsification alone. Additionally, we identified two RCTs that randomized participants to treatment with iStents or to medical interventions. We also identified one RCT that randomized participants to treatment with one iStent, with two iStents, or with three iStents. The manufacturer of the iStent provided funding and sponsorship for all the RCTs in this review.

Based on low-quality evidence, we found that participants who received iStent in combination with cataract surgery were more likely to be drop-free and may have experienced a modest reduction in number of glaucoma drops used per day to control IOP in the medium term, compared with participants who underwent cataract surgery alone; however, there was no difference in average change from baseline in IOP between the two groups.

Due to substantial heterogeneity, we did not conduct an analysis of the two studies comparing treatment with iStent to medical therapy. Investigators of those two studies reported that no participants in the medical therapy group were drop-free at 12 months, compared to over 90% in the iStent treatment groups. Data suggested that treatment of people with two or with three iStents may have been more effective than treatment with one iStent in terms of IOP control.

None of the seven studies included in this review provided information on quality of life, and differences in complications or side effects between treatment groups were uncertain, given few reported events and varied effectiveness.

How up-to-date is the review?
We searched for studies published up to 17 August 2018.