---
title: What is ab externo glaucoma surgery?
description: "Ab externo glaucoma surgery is performed from outside the eye wall, typically involving creation of a new drainage route for aqueous humour under the conjunctiva. It includes operations such as trabeculectomy and non‑penetrating deep sclerectomy. ## Procedures In trabeculectomy, a…"
url: "https://bluefinvision.com/knowledge-base/topics/treatments-procedures/what-is-ab-externo-glaucoma-surgery/"
updated: "2025-12-12"
category: "Treatments & Procedures"
---

# What is ab externo glaucoma surgery?

Ab externo glaucoma surgery is performed from outside the eye wall, typically involving creation of a new drainage route for aqueous humour under the conjunctiva. It includes operations such as trabeculectomy and non‑penetrating deep sclerectomy.

## Procedures

In trabeculectomy, a partial-thickness scleral flap and internal opening are created so fluid can percolate into a subconjunctival bleb, lowering intraocular pressure. Deep sclerectomy and other variants modify this approach to reduce risk of hypotony.

- Often used for moderate to advanced glaucoma needing low target pressures
- Antimetabolites like mitomycin C may be applied to reduce scarring
- Post-operative care involves intensive drop regimens and frequent visits
- Needling or suture adjustment may be required to maintain filtering function

## Benefits and Risks

Ab externo surgery can achieve substantial and long-lasting pressure reduction but carries higher risks than MIGS, including infection, hypotony, bleb leaks, and visual fluctuation.

- Careful patient selection and adherence to follow-up are crucial
- Over- or under‑filtration can require additional interventions
- Despite risks, it remains the gold standard for difficult or advanced glaucoma
- Patients must understand signs of late bleb infection and seek urgent care if they occur