Bleb Grading and Hypotony After Trabeculectomy
Last updated: October 2026
Short answer: after trabeculectomy, the bleb is graded on its size, height, vascularity and leakage. The Indiana and Moorfields systems are the most widely used. Hypotony is usually defined as IOP below about 6 mmHg. It becomes a problem when it causes hypotony maculopathy, with chorioretinal folds and reduced vision, which needs treatment of the underlying cause.
Bleb grading systems
- Indiana Bleb Appearance Grading Scale: grades bleb height, extent, vascularity and leakage on the Seidel test.
- Moorfields Bleb Grading System: grades the central and maximal area of the bleb, its height and its vascularity.
- Photograph blebs at key visits so changes can be compared over time.
Bleb types and what they mean
| Bleb | Appearance | Significance |
|---|---|---|
| Diffuse, moderately vascular | Low, spread out, mild vascularity | The ideal functioning bleb |
| Thin, cystic, avascular | Clear, raised, few vessels (common after antimetabolites) | Risk of leaks, blebitis and endophthalmitis |
| Encapsulated (Tenon's cyst) | Tense, dome-shaped, thick-walled; often appears weeks after surgery | Raised IOP; may respond to needling or medication |
| Flat, scarred | Little or no elevation, vascular | Failing bleb with raised IOP |
Hypotony and hypotony maculopathy
- Definition: IOP below about 6 mmHg is commonly used. Low IOP alone is not always harmful.
- Hypotony maculopathy: reduced vision with chorioretinal folds, optic disc swelling and tortuous vessels. It needs treatment to avoid permanent damage.
- Other complications: shallow anterior chamber, choroidal detachment, and cataract.
Find the cause of hypotony
- Bleb leak: do a Seidel test with concentrated fluorescein.
- Overfiltration without a leak.
- Cyclodialysis cleft (after trauma or surgery): look with gonioscopy or UBM.
- Reduced aqueous production: inflammation, ciliary body detachment, or retinal detachment.
Treatment options
- Bleb leak: aqueous suppressants, reduced steroids, a bandage contact lens, autologous blood injection, compression sutures, or surgical bleb revision.
- Overfiltration: compression sutures, autologous blood, or bleb revision.
- Cyclodialysis cleft: cycloplegia, laser, or surgical closure.
- Treat inflammation and any retinal detachment.
Frequently asked questions
What IOP is considered hypotony?
IOP below about 6 mmHg is the most common definition. It matters most when it causes symptoms or hypotony maculopathy.
What is hypotony maculopathy?
Reduced vision from low IOP, with chorioretinal folds, optic disc swelling and tortuous vessels on examination. It needs treatment of the underlying cause.
What is an encapsulated bleb?
A tense, dome-shaped bleb with a thick wall (a Tenon's cyst), usually appearing in the weeks after surgery. It raises IOP and may respond to medication or needling.
Related: gradings in ophthalmology, bleb-related endophthalmitis and target IOP.
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