What Is Trabeculectomy?

Glaucoma damages the optic nerve slowly, and raised pressure inside the eye is the main force driving that damage. Drops and laser treatment lower the pressure for many people, but when they no longer control it — or the nerve keeps worsening anyway — surgeons can build the eye a new way out for its fluid. That operation is a trabeculectomy. Rather than explaining it in the abstract, it helps to follow it step by step, because each step answers the one before it.

The video at the top of this page, "Glaucoma Trabeculectomy Surgery", is a real operating-microscope recording, a little over six minutes long. Its description frames it plainly: trabeculectomy with mitomycin-C for complex glaucoma. You are watching through the surgeon's microscope, so the eye fills the frame and every movement is small and deliberate — that magnification is exactly how the operation is actually done.

Step one: settling the eye and opening the surface

The eye is numbed first. Depending on the patient and the surgeon, that can mean local anaesthetic around or behind the eye, sometimes with sedation, and occasionally a general anaesthetic. The surface is cleaned, a drape keeps the lashes out of the way, and a small clip holds the eyelids gently open.

Working under the microscope, the surgeon lifts a thin flap in the conjunctiva — the clear skin over the white of the eye — near the top of the eye, usually hidden under the upper lid. That pocket matters later: it is where the drained fluid will collect.

Step two: making a guarded flap in the wall of the eye

Next, the surgeon cuts a small, partial-thickness flap in the sclera, the tough white wall underneath. Think of it less as a hole and more as a trapdoor that is hinged on one side. Its thickness and its stitches are what make this operation "guarded" — the flap resists the flow passing under it, so fluid leaves the eye in a controlled trickle rather than all at once, which would drop the pressure too far, too fast.

A medicine called mitomycin-C is often applied briefly to the area during this stage — it is the adjunct named in the anchor video's description, and the second video linked below shows it in its title too. Its job is to discourage scarring while the area heals, because scar tissue closing over the new channel is the most common reason a trabeculectomy stops working over time.

Step three: the tiny opening and the fluid's new route

Underneath the flap, the surgeon removes a very small block of tissue at the edge of the cornea, creating an opening into the front chamber of the eye, and usually makes a small opening in the iris beneath it so the iris cannot plug the gap. The flap is then laid back down and stitched with fine sutures — sometimes ones that can be loosened or removed later with a laser, so the flow can be fine-tuned after surgery.

From then on, the aqueous fluid that the eye constantly produces has two routes out: its natural drain, and this new one. Fluid seeps under the flap and gathers in the pocket under the conjunctiva, forming a soft, slightly raised area called a bleb, usually under the upper lid where you cannot see it. From the bleb, the fluid is gradually absorbed into the surrounding tissues. Our overview of glaucoma and how it is treated sets this operation in context alongside drops and laser treatment.

A second recording on this site, "Trabeculectomy with MMC" from the Mohamed Ibrahim channel, shows the same operation built around a triangular, fornix-based flap in primary open-angle glaucoma — a useful reminder that surgeons vary the flap details while the underlying idea stays the same.

Step four: the weeks afterwards, when the result is decided

A trabeculectomy is not finished when the stitches are in. The first weeks involve frequent check-ups, because the team is watching two things at once: that the pressure is coming down, and that the bleb is healing open rather than scarring shut — and not draining so freely that the pressure falls too low. Drops are used during healing, some of your usual glaucoma drops may be stopped for the operated eye, and the adjustable stitches give the surgeon a way to increase flow if the pressure is still higher than intended.

You will be told to protect the eye, avoid rubbing it, and keep to the drop routine and appointments even when the eye feels comfortable — a healing bleb can feel like nothing at all while it quietly scars. Vision in the operated eye is often blurry at first and settles gradually. Tell your team promptly about increasing pain, redness, discharge, a sudden drop in vision, or a blow to the eye, because a bleb is a deliberate, thin-walled channel and infection in it needs urgent treatment.

Done well, the reward for all this care is an eye whose pressure stays lower day and night, without relying on the drops that were no longer enough. For comparison, the operation most people know better, cataract surgery, is covered in our guide to cataracts and how they are removed — a different operation entirely, though the two are sometimes discussed in the same clinic visit.

References & further reading

• MedlinePlus — Glaucoma: https://medlineplus.gov/glaucoma.html
• NHS — Glaucoma: https://www.nhs.uk/conditions/glaucoma/
• National Eye Institute — Glaucoma: https://www.nei.nih.gov/learn-about-eye-health/eye-conditions-and-diseases/glaucoma
• American Academy of Ophthalmology — What Is Glaucoma?: https://www.aao.org/eye-health/diseases/what-is-glaucoma

Frequently Asked Questions

Is trabeculectomy the same as laser treatment for glaucoma?
No. Laser treatments work on the eye's natural drain or on fluid production, from outside or with a fine probe, and involve no new opening. A trabeculectomy is an operation that builds a new, guarded drainage channel under a flap, with fluid collecting in a bleb under the surface. It is generally considered when drops and laser no longer control the pressure.

What is a bleb, and will I see it?
A bleb is the small, soft reservoir where fluid collects after passing under the flap, before being absorbed. It usually sits under the upper eyelid, so most people cannot see it in the mirror and other people would not notice it. Your surgeon will check it at every follow-up visit, because its shape and appearance say a lot about how the operation is healing.

Will I still need glaucoma drops afterwards?
Possibly not for the operated eye, possibly some. The aim is pressure control with fewer drops or none, but healing varies, and the team may restart a drop if the pressure creeps back up. Never stop or restart drops in either eye on your own — the plan is set at your check-ups, eye by eye.

What can make a trabeculectomy stop working?
Scarring. The body reads the new channel as a wound and tries to close it, which is why an anti-scarring medicine is often used during surgery and why the early follow-up visits matter so much. If the channel scars down and pressure rises again, there are further options your surgeon can discuss, from needling procedures to other operations.

MedicalVideos.com has published trusted medical videos since 2007. The site was founded by Dr. Mohamed Ibrahim, MD, PhD — physician-scientist.

Educational only — this article is general information about trabeculectomy, not medical advice and not a diagnosis. Whether this operation, or any treatment, is right for you is a matter for your own care team, who know your results and your history.