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
