Phacoemulsification with and without iStent: A Systematic Review and Meta-Analysis of Comparative Studies

Author: Kahale F, Chanbour W, El Zein L, Brenner J, You JY, Melki S.

Geographical coverage: The USA, UK, Italy, Spain, Germany, and Switzerland

Sector: Biomedical

Sub-sector: Treatment comparison

Equity focus: Not reported

Study population: Patients with cataract

Review type: Effectiveness review

Quantitative synthesis method: Meta-analysis

Qualitative synthesis method: Not applicable

Background: Glaucoma is the leading cause of permanent blindness throughout the world and is commonly linked to elevated intraocular pressure (IOP), which is the only modifiable risk factor for its progression. While topical IOP-lowering drops are a mainstay treatment, but issues like ocular irritation and noncompliance reduce their effectiveness. To overcome this issue, minimally invasive glaucoma surgeries, such as iStent implantation, are an alternate way to enhance aqueous outflow through Schlemm’s canal. The iStent can be used alone or during phacoemulsification (which is a standard cataract surgery). Both iStent and phacoemulsification independently lower IOP, therefore, their combined effect may offer enhanced outcomes. Available literature lacks direct comparison with standalone phacoemulsification, therefore, a rigorous comparative evaluation is crucial to check and understand their relative benefits in managing open-angle glaucoma and ocular hypertension.

Objective: To compare the effect of iStent insertion at the time of phacoemulsification with phacoemulsification alone in patients with ocular hypertension or open-angle glaucoma.

Main findings: In total, 10 studies (853 eyes) met the inclusion criteria and were included in this review. Eight of the 10 included studies were randomised controlled trials, one was a retrospective cohort study, and one was a retrospective case series. The studies were conducted in the USA (n=4), England (n=1), Italy (n=2), Spain (n=1), Germany (n=1), and Switzerland (n=1). The quality index scores of the included studies ranged from 0.57 to 0.78.

All studies reported a larger decrease in the mean number of glaucoma drops use after combined surgery with a weighted mean drop reduction of 1.2 ± 0.3 drops compared with isolated phacoemulsification with a weighted mean drop reduction of 0.6 ± 0.6 drops. The majority of the studies (9 of 10) reported higher IOPR in the combined surgery with a weighted mean intraocular pressure reduction (IOPR) of 4.7 ± 2.1 mm Hg compared with phacoemulsification alone having a weighted mean IOPR of 2.8 ± 1.9 mm Hg.

The quality effect model showed an IOPR weighted mean difference (WMD) of 1.22 mm Hg (confidence interval [CI]: –0.43 to 2.87, p < 0.01, I² = 97%) and decreased eye drops WMD 0.42 drops (CI: 0.22 to 0.62, p < 0.01, I² = 84%) between both surgical groups.

Methodology:  The searches were conducted in Medline, Embase, CINHAL, and the Cochrane Library without any language limits between 2008 and June 2022. The studies were included if they were Clinical trials, randomised controlled trials, prospective and retrospective cohorts, or case series, and compared isolated phacoemulsification and combined phacoemulsification and iStent.

Two reviewers independently screened the articles, extracted the relevant data. Disagreements between the reviewers were resolved through discussion or by contacting a third reviewer. The study quality was assessed using the Downs and Black checklist. The findings were synthesised using meta-analysis, heterogeneity was assessed using the Cochrane Q-test and I² statistics, and publication bias was assessed using a funnel plot.

Applicability/external validity: The review noted that the included studies were conducted in the USA and Europe. Additionally, it noted high heterogeneity between the studies, as well as possible publication bias. The review emphasised the need for further studies to assess the long term IOP-lowering effect of iStent, the protective effect on the optic nerve, and how long it may delay the need for future, more invasive, glaucoma surgeries.

Geographic focus: The review did not apply any geographical limits. The included studies were conducted in the USA, UK, Italy, Spain, Germany, and Switzerland.

Summary of quality assessment: Overall, there is medium confidence in the conclusions about the effects of this study. The searches were conducted in Medline, Embase, CINHAL, and the Cochrane Library without any language limits between 2008 and June 2022. Inclusion and exclusion criteria were clearly defined, and two reviewers independently screened the articles and extracted data. The study quality was assessed using established tools. Characteristics of included studies were well-documented, meta-analyses were appropriately performed, and heterogeneity was addressed. However, the review did not report checking the reference lists of the included studies, nor did it provide a list of excluded studies. Additionally, the review did not analyse/report the findings by the risk of bias status.