When is evidence enough evidence? A systematic review and meta-analysis of the Trabectome as a solo procedure in patients with primary open-angle glaucoma

Methodological quality of the review: Low confidence

Authors: Chow JTY, Cindy M L Hutnik CML, Solo K, Malvankar-Mehta MS

Region: Canada, Japan, Mexico and USA

Sector:  Glaucoma

Sub-sector:  Treatment

Equity focus: None specified

Review type: Other review

Quantitative synthesis method: Meta-analysis

Qualitative synthesis method: Not applicable

Background:

Surgery is typically required when medication and laser treatments fail to deliver the necessary reduction in IOP in glaucoma patients. Minimally invasive glaucoma surgeries (MIGS) have become more popular due to their perceived safety and lack of complications. One of these MIGS is the Trabectome surgical system developed by NeoMedix Inc. in Tustin, CA.

Objectives:

The purpose of this systematic review and meta-analysis was to examine the availability of evidence for one of the earliest available minimally invasive glaucoma surgery (MIGS) procedures, the trabectome.

Main findings:

The authors included three studies and one abstract in the meta-analysis. Though the full text was in German, the abstract was included since there was sufficient information in the abstract. All studies measured IOP and glaucoma medications at baseline and post-operative time points with subgroups for POAG and pseudoexfoliation glaucoma (XFG) patients.

Of the studies that looked at the effect of intraocular pressure, the authors found significant heterogeneity between studies examining one month follow-up  (I² = 88.5%, p value = 0.03), but nonsignificant heterogeneity between studies examining six months follow-up (I² = 0.0%, p value = 0.958) and 12 months follow-up (I² = 39.6%, p value = 0.191). In addition, the authors also found a non-statistically significant reduction in IOP with SMD of -1.66 at  one month and a statistically significant reduction in IOP with a SMD of -1.31 at six months and -1.35 at 12 months. Overall, this suggests that the significant reduction in IOP from the trabectome procedure persists even after 12 months.

Of the studies that analysed change in glaucoma medications, two studies considered follow-up of six months and three studies inspected 12-months follow-up.  Nonsignificant heterogeneity between studies examining follow-up at one month (I² = 32.8%, p value = 0.223), six months (I²= 0.0%, p value = 0.694), and 12 months (I² = 0.0%, p value = 0.934) was used to determine the fixed-effect computations. The authors found that there was a statistically significant reduction in post-operative glaucoma medications used with a SMD of −0.18 (CI: [−0.31, −0.05]) at one month, SMD of −0.43 (CI: [−0.56, −0.31]) at six months, and a SMD of −0.45 (CI: [−0.56, −0.33]) at 12 months follow-up. Thus, trabectome surgery may significantly reduce dependence on glaucoma medications at 12 months follow-up.

Methodology: 

Searches were conducted in several databases including PubMed, MEDLINE, EMBASE, Web of Science Core Collection, and CINHAL from inception to December 2016. Grey literature was identified by searching ClinicalTrials.gov, the International Clinical Trials Registry Platform, ProQuest Dissertations and Theses, the Networked Digital Library of Theses and Dissertations, the Electronic Thesis Online Service, the Theses Canada Portal, the Canadian Health Research Collection, the Agency for Healthcare Research and Quality, and the Canadian Agency for Drugs and Technologies in Health for all relevant studies. BIOSIS Previews (using the Web of Science platform), the Association for Research in Vision and Ophthalmology (ARVO), the American Academy of Ophthalmology (AAO), and the Canadian Ophthalmological Society (COS) were searched for meeting abstracts that met the criteria described in the database search.

Inclusion criteria consisted of primary research studies presenting outcomes for the trabectome as a solo procedure in humans with POAG. No restrictions were made on study location or year of publication. Studies were included if they were published in English and had a sample size over 20. Two reviewers independently screened studies for inclusion. All included studies except for the abstract-only study were assessed for quality using the Downs and Black checklist.

Percentage of IOP reduction (IOPR%) and standard error of percentage of IOP reduction (SEIOPR%) were calculated using the extracted IOP and standard deviation at each time point according to equations described in similar studies. The outcomes of interest were the standardized mean differences (SMD) for change in intraocular pressure and change in glaucoma medications at six-month and 12-month follow-up. Based on I² statistics and p values (>0.01) observed, heterogeneity was determined and fixed-effect or random-effect models were used accordingly. Forest plots were generated for each outcome of interest, and funnel plots were generated to check for publication bias.

Applicability/external validity:

In all included studies, the results suggested that the trabectome surgery resulted in significant reduction in IOP and glaucoma medications in POAG patients

Geographic focus

The authors did not report geographic focus of all included studies, therefore it is not possible to discuss applicability of findings to low- and middle-income countries.

Summary of quality assessment:

Overall, there is low confidence in the conclusions about the effects of this review. The authors used comprehensive methods to search for the literature to ensure that all relevant studies were included in the review. However, it is not clear the risk of bias of included studies was considered, therefore impacting on the reliability of included studies. In addition, it is not clear from the review if the authors used rigorous methods to extract data of included studies.