Non-penetrating glaucoma surgery: a meta-analysis of recent results

Methodological quality of the review: Low confidence

Author: Hondur A, Onol M, Hasanreisoglu B

Geographical coverage: Not reported

Sector: Glaucoma

Sub-sector: Non-penetrating glaucoma surgery

Equity focus: None specified

Review type: Effectiveness review

Quantitative synthesis method: Meta-analysis

Qualitative synthesis method: Not applicable

Background: For non-penetrating glaucoma surgery (NPGS), many modifications of both deep sclerectomy (DS) and viscocanalostomy (VC) have been introduced to facilitate intra-ocular pressure (IOP)-lowering efficacy. Many implants have also been used in the scleral space or in Schlemm’s canal, as well as anti-metabolite application. There is a need for clinical validation of DS and VC.

Objectives: To evaluate the efficacy of NPGS for open angle glaucoma with respect to target intra-ocular pressure (IOP) and severity of glaucoma.

Main findings: In this review, 30 studies were included. The percentage of cases achieving ≤21 mm Hg was 48.6% after primary DS, 68.7% after DS with implant, 67.1% after DS with anti-metabolite, 51.1% after primary VC and 36.8% after VC with anti-metabolite or implant.

Visual field parameters were almost exclusively not available, whereas cup/disk ratio and target IOP lower than 21 mm Hg were available in very few reports. With lower-set IOP targets, the rates of success varied between 35% and 86% for DS, and between 10% and 67% for VC. The mean follow-up of the studies was mostly in the range of three years.

The use of NPGS at an early stage of glaucoma has the benefit of avoiding adverse effects of anti-glaucoma medications on surgical success. In addition, the achievement of IOP targets in the high teens could be adequate to stop the progression of glaucoma. Authors note that longer-term studies, with data related to glaucoma severity and proper target IOPs, are required.

Methodology: MEDLINE was searched for ‘non-penetrating glaucoma surgery’, ‘deep sclerectomy (DS)’, ‘viscocanalostomy (VC)’ and ‘open angle glaucoma’. Studies encompassing only combined glaucoma and cataract surgery were excluded. To avoid any duplication of results, multiple clinical reports – including the same cases from a single centre, the study with the largest number of cases with longer follow-up or with more clear results – was evaluated, and others excluded. Measurement of effectiveness was determined on the basis of achievement of target IOP. Data related to post-operative goniopuncture and needling with anti-metabolite application was noted.

Applicability/external validity: No methods were used either to assess the applicability/external validity of the results or to discuss how generalizable the results are.

Geographic focus: This review focuses on all countries, as authors did not restrict the search to specific countries.

Summary of quality assessment: Low confidence was attributed in conclusions about the effects of this study as major limitations were identified. Authors did not conduct a thorough search of the literature as only MEDLINE was searched. Restriction bias was not avoided as authors included studies written in English only, and only published studies were searched for. Methods used to sift studies for inclusion, study selection, appraisal and synthesis was not clear from the review.