Anterior segment imaging in minimally invasive glaucoma surgery – A systematic review

Author: Kan JT, Betzler BK, Lim SY, Ang BCH.

Geographical coverage: Italy, Spain, Switzerland, the USA, Austria, Japan, Canada, Germany, and India.

Sector: Glaucoma treatment

Sub–sector: Anterior segment imaging

Equity focus:  Not reported

Study population: Patients with glaucoma

Review type: Effectiveness review

Quantitative synthesis method: Narrative synthesis

Qualitative synthesis method: Not applicable

Background:

Glaucoma, a leading cause of irreversible blindness, is increasingly prevalent. Traditional treatments such as medication and laser therapy are effective in lowering intraocular pressure (IOP), while advanced cases often require more invasive procedures like trabeculectomy. However, minimally invasive glaucoma surgery (MIGS) has emerged in recent years and is gaining popularity due to its IOP-lowering efficacy and superior safety profile compared with traditional glaucoma surgeries.

Objectives:

To explore the peri-operative and intraoperative application of anterior segment imaging to maximise the efficacy and safety of MIGS.

Main findings:

Overall, anterior segment imaging holds significant potential to enhance the safety, efficacy, and clinical outcomes of MIGS despite current technological and practical limitations.

A total of 570 records were identified from the electronic database, of which 21 studies were included in this review. Eleven of the 21 included studies were case series, seven were case reports, two were prospective, and one was an observational study. The included studies were conducted in Italy, Spain, Switzerland, the USA, Austria, Japan, Canada, Germany, and India. Imaging was predominantly applied postoperatively (19 of 21 studies), while intraoperative imaging was reported in three studies, and preoperative imaging was the least common, reported in only one study.

Anterior segment imaging modalities included anterior segment optical coherence tomography, ultrasound biomicroscopy, aqueous angiography, optical coherence tomography volumetric scans and in vivo confocal microscopy. Identification and evaluation of aqueous outflow pathways before and after MIGS have the potential to enhance preoperative patient selection and improve postoperative outcomes. Intraoperative imaging potentially provides the resolution needed for good visualisation of angle anatomy and accurate evaluation of surgical endpoints in angle-based MIGS.

Anterior segment imaging has been used to identify procedural complications, provide objective information on implant location in relation to surrounding anatomy, assess the post-implantation structural impact of MIGS devices and manage bleb failure and scarring. Technical difficulties in incorporating imaging modalities into the surgical microscope, variable quality of images, and optical interference from ocular structures or surgical instruments are remaining barriers that discourage widespread clinical use of this technology.

Methodology:

The literature search was conducted in PubMed, EMBASE, and CINAHL, by two review authors, to retrieve studies reporting on MIGS devices and procedures that create subconjunctival outflow, increase trabecular outflow, and decrease aqueous production; excluding the CyPass Micro-Stent, which was recalled due to safety concerns. Only human studies published in English, spanning from the inception of the databases to April 21, 2020, were included. A secondary search of the references of all retrieved articles and review articles was performed to identify other potentially relevant studies. The studies were independently assessed by three reviewers, and discrepancies were resolved through a discussion with a senior reviewer. The findings were synthesised narratively.

Applicability/external validity:

The study’s comprehensiveness is limited by data heterogeneity, preventing a meta-analysis, and its focus solely on FDA-approved MIGS excludes other valuable procedures. This narrows the scope, potentially affecting the generalisability and applicability of the findings.

Geographic focus:

The included studies were conducted in Italy, Spain, Switzerland, the USA, Austria, Japan, Canada, Germany, and India.

Summary of quality assessment:

There is low confidence in the conclusion of this review. Despite thorough literature searches, only English studies were included. Additionally, the risk of bias in the studies was not assessed, and the methods for data extraction remain unclear.