Risks of Trabeculectomy

If trabeculectomy works so well, why don’t glaucoma surgeons recommend it to all of their patients with glaucoma?  After all, cataract surgeons offer cataract surgery to nearly every one of their patients with a significant cataract.  What’s so different about glaucoma?  Well, for one, cataract surgery is intended to improve vision whereas glaucoma surgery is meant only to delay loss of vision.  As such, the upside of glaucoma surgery is limited whereas the downside (risk) can be quite significant.  And, of all glaucoma surgeries, trabeculectomy carries some of the greatest risk.  Thus, it is not recommended lightly.

So, what are these risks?  There are quite a few, so it’s best to split them into categories: intraoperative (during surgery), early postoperative (as the eye is healing from surgery), and late postoperative (after the eye has healed from surgery).  Please note that this list is not exhaustive.  Other risks of trabeculectomy have been reported but the following may be considered the main ones.


Risks of Trabeculectomy

Intraoperative (during surgery)

Bleeding is the main concern during surgery.  Minor amounts of bleeding at the incision site can make surgery more challenging.  The main concern, however, is the much-feared choroidal or expulsive hemorrhage.[1]  An expulsive hemorrhage is just what it sounds like: a sudden bleed that forces the contents inside of the eye out.  This risk actually exists with all eye surgeries including cataract surgery though it is more commonly encountered with glaucoma surgeries due to the sudden drop in IOP that occurs during surgery.

Early postoperative (as the eye is healing from surgery)

Speak to most patients who have undergone trabeculectomy and they will tell you that the early postoperative period is a royal pain – and that’s even if they do not have any complications.  “Normal” postoperative care involves use of drops multiple times each day as well as many visits to the glaucoma surgeon.  Activities must be severely curtailed during the healing process (no exercising, bending, lifting, etc.).  Add a complication and expect this to become the short-term focus of your life.  How so?  Let’s take a look at what can happen early after trabeculectomy surgery.

Hypotony (extremely low IOP)

Hypotony is simply an intraocular pressure (IOP) that is too low.  “Too low?!” you say, “I thought the whole point of trabeculectomy is that it lowers the IOP better than any other surgery?” and you’d be correct.  It’s also more likely than most other glaucoma surgeries to result in a dangerously low IOP.

What is the problem with an IOP that is too low?  That depends upon how low it is.  If it is zero then the structures in the eye can collapse allowing the lens to touch the cornea.  This can result in both a cataract and corneal damage, both of which can worsen vision.  Slightly higher (but still very low) pressures can damage the central retina.  This is called hypotony maculopathy and can result in permanent loss of central vision.

Hypotony is one of the more common risks associated with trabeculectomy.  This risk increases with use of Mitomycin-C (MMC).  One study noted over 40% of patients experienced hypotony (IOP<6mmHg) between six months and five years out from trabeculectomy with MMC use.[2]

Elevated IOP

Your eye is a bit like Goldilocks: it needs an IOP that is neither too low nor too high.  Although the entire point of glaucoma surgery is to lower the IOP, early after surgery the IOP can actually rise higher than it was prior to surgery.   If the IOP rises too high that could result in additional loss of visual field.  This is true for any glaucoma surgery and is generally the result of the body’s attempt to undo what your surgeon did (healing response).  Fortunately these IOP spikes are most often transient or treatable by your surgeon.

Delayed bleeding

It is very important to take it easy for at least the first few weeks after surgery.  Bending, lifting, jumping, or other exertional activities should be avoided.  Coughing, sneezing, vomiting, and even constipation should also be controlled.  Why?  Because such activities can result in sudden, severe, vision-threatening bleeding in the eye.  This type of bleeding in the eye is generally very painful and may even cause nausea.  If you experience a sudden, painful loss of vision after surgery it is very important that you call your surgeon right away.  This condition is not easy to treat and few eyes fully recover vision[3] but the earlier it is treated the better the chance of saving vision.

Failing bleb

Some might argue that a failed bleb is not really a risk but an expected outcome.  After all, the body wants to seal off the fistula and scar down the bleb.  Indeed, bleb failure is the most common cause of trabeculectomy failure.[4]  What’s amazing is that blebs can last as long as they do when they do last.

Early after surgery the body mounts an aggressive inflammatory reaction which can quickly result in scarring of the bleb.  This is generally treated with topical steroids.  If scarring is already present the the surgeon may try maneuvers such as “massaging” or “needling” the bleb, both of which can be done in the office.  As might be deduced from the names of these techniques, they aren’t very comfortable when performed on an inflamed eye.

Loss of vision

Although the entire purpose of trabeculectomy is to save vision, there is a small, but real, risk of  permanent loss of vision noted immediately after surgery.  There are two main causes of this:

Decompression retinopathy[5]

If the IOP prior to surgery is very high then the sudden decrease in IOP from surgery can actually lead to bleeding into the retina.  If severe, loss of vision could be permanent.

“Snuff Out” Syndrome[6]

This horribly named syndrome describes a sudden loss of vision noted early on after surgery.  It is more common in older patients who have very advanced (severe) glaucoma with central visual field loss prior to surgery.  Fortunately, it is rare (occurs in less than 1% of patients who have trabeculectomy).


1) Speaker MG, Guerriero PN, Met JA, et al. A case-control study of risk factors for intraoperative suprachoroidal expulsive hemorrhage. Ophthalmology. 1991;98(2):202-209.

The Fluorouracil Filtering Surgery Study Group. Risk factors for suprachoroidal hemorrhage after filtering surgery. Am J Ophthalmol. 1992;113(5):501-507.

2)  Bindlish R, Condon GP, Schlosser JD, et al. Efficacy and safety of mitomycin-C in primary trabeculectomy: five-year follow-up. Ophthalmology. 2002;109(7):1336-1341; discussion 1341-1342. 

3) Tuli SS, WuDunn D, Ciulla TA, et al. Delayed suprachoroidal hemorrhage after glaucoma filtration procedures. Ophthalmology. 2001;108(10): 1808-1811.

4) Maumenee AE. External filtering operations for glaucoma: the mechanism of function and failure. Trans Am Ophthalmol Soc. 1960;58:319-328. 

5)  Fechtner RD, Minckler D, Weinreb RN, et al. Complications of glaucoma surgery. Ocular decompression retinopathy. Arch Ophthalmol. 1992; 110(7):965-968.

Dudley DF, Leen MM, Kinyoun JL, et al. Retinal hemorrhages associated with ocular decompression after glaucoma surgery. Ophthalmic Surg Lasers. 1996;27(2):147-150.

Suzuki R, Nakayama M, Satoh N. Three types of retinal bleeding as a complication of hypotony after trabeculectomy. Ophthalmologica. 1999;213(2):135-138.

Danias J, Rosenbaum J, Podos SM. Diffuse retinal hemorrhages (ocular decompression syndrome) after trabeculectomy with mitomycin C for neovascular glaucoma. Acta Ophthalmol Scand. 2000,78(4):468-469.

Karadimas P, Papastathopoulos KI, Bouzas EA. Decompression retinopathy following filtration surgery. Ophthalmic Surg Lasers. 2002;33(2):175-176.

Cordido Carballido M, Alvarez Martinez E, Lopez Rodriguez I, et al. Ocular decompression retinopathy after trabeculectomy [in Spanish]. Arch Soc Esp Oftalmol. 2002;77(6):331-334.

6)  Lichter PR, Ravin J.G. Risks of sudden visual loss after glaucoma surgery. Am J Ophthalmol. 1974;78(6):1009-1013.

Aggarwal SP, Hendeles S. Risk of sudden visual loss following trabeculectomy in advanced primary open-angle glaucoma. Br J Ophthalmol. 1986;70(2):97-99.

Costa VP, Smith M, Spaeth GL, et al. Loss of visual acuity after trabeculectomy. Ophthalmology. 1993;100(5):599-612.

Martinez JA, Brown RH, Lynch MG, et al. Risk of postoperative visual loss in advanced glaucoma. Am J Ophthalmol. 1993;115(3):332-337.

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