Glaucoma surgery can be highly effective at lowering eye pressure and protecting the vision that remains, but no eye operation is completely free from risk. The possible complications range from temporary problems that settle during healing to uncommon but serious events that can affect vision.
*AI-generated image - for illustration only. Clinical accuracy is not guaranteed.
The level and type of risk depend greatly on the operation being performed. For example, trabeculectomy, glaucoma drainage implants and minimally invasive glaucoma surgery (MIGS) have different complication profiles.
The condition of the eye also matters. Previous eye surgery, inflammation, glaucoma severity, scarring tendency and other eye diseases can all influence surgical risk. For an overview of the available procedures and how they lower eye pressure, see our main guide to Glaucoma Surgery.
How Risky Is Glaucoma Surgery?
Most glaucoma surgery complications are manageable, and many are temporary. However, traditional glaucoma operations such as trabeculectomy and tube-shunt surgery are more complex than procedures such as laser treatment and most MIGS procedures.
A major five-year randomized study comparing trabeculectomy with tube-shunt surgery found that postoperative complications were relatively common when every minor and major event was counted, but most complications were temporary and resolved without permanent consequences.
In that study:
- Early complications occurred in approximately 34% of trabeculectomy patients and 19% of tube-shunt patients
- Late complications occurred in approximately 27% of trabeculectomy patients and 22% of tube-shunt patients
- Serious complications causing vision loss and/or requiring another operation occurred much less frequently
Early vs Late Glaucoma Surgery Complications
It is useful to divide complications according to when they occur.
| Early Complications | Later Complications |
|---|---|
| Low eye pressure | Scarring and loss of drainage |
| High eye pressure | Late bleb leakage |
| Bleeding inside the eye | Bleb-related infection |
| Shallow anterior chamber | Tube exposure or movement |
| Choroidal fluid collection | Corneal damage |
| Inflammation | Cataract progression |
Some complications can occur during either period, so regular follow-up remains important long after the eye appears to have healed.
1. Eye Pressure That Becomes Too Low
Glaucoma surgery is designed to lower intraocular pressure, but occasionally the new drainage pathway works too well. This is called hypotony. It is particularly associated with filtering operations such as trabeculectomy and can also occur after certain glaucoma drainage procedures. Very low pressure can lead to:
- Blurred vision
- A shallow front chamber of the eye
- Changes in the shape of the eye
- Choroidal effusion
- Macular folds or hypotony maculopathy
2. Shallow or Flat Anterior Chamber
The anterior chamber is the fluid-filled space between the cornea and iris. If pressure becomes very low after glaucoma surgery, this space can become unusually shallow. If the iris or lens moves too close to the cornea, there is a risk of further complications. Management depends on the cause and severity and may include:
- Medication
- Reducing excessive drainage
- Reforming the anterior chamber with fluid or viscoelastic material
- Additional surgery in more serious cases
3. Choroidal Effusion or Detachment
The choroid is a vascular layer toward the back of the eye. Very low eye pressure can allow fluid to collect between the choroid and the outer wall of the eye. This is called a choroidal effusion or choroidal detachment. Many small effusions resolve as eye pressure normalizes. Larger or persistent detachments may affect vision or the internal structure of the eye and occasionally require drainage.
4. Suprachoroidal Hemorrhage
A suprachoroidal hemorrhage is a rare but serious complication in which significant bleeding develops within the deeper layers of the eye. It may occur during surgery or shortly afterward. Possible warning signs include:
- Sudden severe eye pain
- Sudden loss of vision
- Changes in the depth or structure of the eye
This complication requires urgent ophthalmic management and may sometimes require additional surgery. Although serious, it is much less common than routine postoperative problems such as temporary inflammation or mild bleeding.
5. High Eye Pressure After Surgery
It may seem surprising that pressure can become high immediately after an operation designed to lower it. Possible causes include:
- Inflammation
- Blood blocking the drainage pathway
- Retained viscoelastic material
- Scar formation
- A blocked tube or stent
- The normal early healing phase of certain drainage implants
6. Bleeding Inside the Eye
One of the more common early complications of several glaucoma procedures is hyphema, meaning blood collects in the front chamber of the eye. This is particularly common after procedures that operate directly on the trabecular meshwork, including some MIGS procedures. Small amounts of blood often clear naturally.
More significant hyphema can:
- Blur vision
- Temporarily increase eye pressure
- Take longer to resolve
7. Infection After Glaucoma Surgery
Infection is uncommon but potentially serious. An infection involving the inside of the eye is called endophthalmitis. Without rapid treatment, it can permanently damage vision. Possible symptoms include:
- Increasing eye pain
- Increasing redness
- Rapid deterioration in vision
- Severe light sensitivity
- Discharge
8. Bleb Infection After Trabeculectomy
Trabeculectomy creates a drainage area underneath the upper eyelid known as a bleb. Unlike many ordinary surgical wounds, this drainage structure remains permanently present.
For this reason, infection can occasionally develop months or even years after surgery. Infection limited to the bleb is often called blebitis. If infection spreads into the eye, endophthalmitis can develop. A patient who has previously undergone trabeculectomy should therefore seek urgent assessment for a red, painful eye accompanied by worsening vision—even if the operation took place years earlier.
9. Bleb Leakage
The surface tissue over a trabeculectomy bleb can occasionally become thin and develop a leak. A leaking bleb may cause:
- Low eye pressure
- Watering
- Discomfort
- An increased risk of infection
10. Scarring and Surgical Failure
One of the most important long-term risks of glaucoma surgery is not a dramatic complication but simply that the drainage pathway gradually stops working. The body naturally tries to heal surgical wounds. After trabeculectomy, excessive scar tissue can close the drainage pathway and cause eye pressure to rise again.
11. Cataract Progression
Cataracts commonly develop with age, but traditional glaucoma surgery can accelerate cataract progression in some patients. A cataract makes the natural lens of the eye cloudy and can lead to:
- Progressively blurred vision
- Glare
- Reduced contrast
- Difficulty seeing at night
12. Corneal Damage
The cornea is the clear front window of the eye. Glaucoma surgery can sometimes affect the endothelial cells that help keep the cornea clear. If enough endothelial cells are damaged, the cornea may become swollen and cloudy.
This risk is particularly relevant with certain glaucoma drainage implants because the tube sits inside the eye near the cornea. Long-term monitoring may therefore include assessment of:
- Tube position
- Corneal clarity
- Corneal thickness
- Endothelial health when clinically necessary
13. Tube Exposure or Erosion
Glaucoma drainage-device surgery leaves a permanent tube inside the eye. The tube is normally covered by tissue, but that tissue can occasionally become thin or break down. This is called tube erosion or tube exposure.
An exposed tube is important because it creates a pathway through which infection can potentially enter the eye. Treatment generally involves surgical repair rather than simply observing the exposed tube.
14. Tube Blockage or Movement
A glaucoma tube may occasionally become:
- Blocked
- Retracted
- Displaced
- Positioned too close to another eye structure
A blocked tube may cause pressure to rise again. A poorly positioned tube may irritate the cornea, iris or other structures. Some cases can be observed or treated with laser, while others require surgical repositioning or revision.
15. Double Vision After Tube-Shunt Surgery
Some patients develop diplopia, or double vision, after glaucoma drainage implant surgery. The implant plate sits beneath the tissues surrounding the eye and may occasionally affect normal eye movement. Scarring around the implant can also contribute.
Persistent troublesome double vision may be managed with:
- Prism glasses
- Observation if symptoms are improving
- Eye-muscle treatment
- Revision of the implant in selected cases
16. MIGS Risks and Complications
Minimally invasive glaucoma surgery generally causes less tissue disruption than trabeculectomy or conventional tube surgery. This gives many MIGS procedures a favourable safety profile. However, MIGS does not mean risk-free surgery.
Depending on the specific operation, complications can include:
- Hyphema
- Temporary eye-pressure spikes
- Inflammation
- Peripheral anterior synechiae, where tissues in the drainage angle stick together
- Corneal swelling
- Damage to Descemet's membrane
- Device malposition in procedures involving implants
- Insufficient eye-pressure reduction
Is MIGS Safer Than Traditional Glaucoma Surgery?
Generally, yes. Many MIGS procedures were specifically designed to reduce the complications associated with traditional filtering surgery. They often offer:
*AI-generated image - for illustration only. Clinical accuracy is not guaranteed.
- Smaller incisions
- Less disruption of the outer eye tissues
- Faster recovery
- Lower risk of severe hypotony
- Lower risk of bleb-related complications for procedures that do not create a bleb
But the trade-off is important. Many MIGS procedures lower eye pressure less than trabeculectomy. For advanced glaucoma requiring a very low target pressure, accepting the greater risks of traditional surgery may provide a better chance of protecting the remaining vision.
Can Glaucoma Surgery Cause Permanent Vision Loss?
Yes, but permanent severe vision loss is uncommon. Vision can potentially be affected by complications such as:
- Severe infection
- Suprachoroidal hemorrhage
- Persistent hypotony
- Significant corneal damage
- Other serious intraocular complications
Does Surgery Carry More Risk Than Leaving Glaucoma Untreated?
This is the most important comparison. Glaucoma surgery is generally recommended because doctors believe that the risk of allowing pressure to remain uncontrolled is greater than the expected risk of surgery. Progressive glaucoma can permanently destroy optic nerve fibres.
Once that vision is lost, current treatment cannot restore it. Therefore, avoiding surgery simply because complications are possible can sometimes carry a greater long-term risk than proceeding with an appropriately selected operation.
Who Has a Higher Risk of Glaucoma Surgery Complications?
Risk varies from one eye to another. Factors that may influence complications or surgical failure include:
- Previous glaucoma surgery
- Other previous eye operations
- Significant conjunctival scarring
- Uveitis or other active inflammation
- Neovascular glaucoma
- Very advanced glaucoma
- Previous eye trauma
- Corneal disease
- A strong individual scarring response
- Other medical or ocular conditions
Why Follow-Up Is So Important After Glaucoma Surgery
Glaucoma surgery does not end when the patient leaves the operating room. The healing period is an active part of the treatment. This is especially true after trabeculectomy. During follow-up, the surgeon may need to:
*AI-generated image - for illustration only. Clinical accuracy is not guaranteed.
- Adjust medications
- Release or modify sutures
- Treat excessive scarring
- Manage low or high eye pressure
- Check for leaks
- Monitor the cornea
- Assess the tube or drainage bleb
Warning Signs After Glaucoma Surgery
Contact an ophthalmologist urgently if you develop:
*AI-generated image - for illustration only. Clinical accuracy is not guaranteed.
- Sudden or rapidly worsening vision
- Severe or increasing eye pain
- Increasing redness
- Significant discharge
- Marked light sensitivity
- Sudden new swelling
- Severe headache with eye pain
- Nausea or vomiting associated with severe eye symptoms
A red and painful eye with reduced vision is particularly important after trabeculectomy because bleb-related infection can occur even long after the original operation.
Comparing the Main Glaucoma Surgery Risks
| Procedure | Important Risks | General Risk Profile |
|---|---|---|
| Trabeculectomy | Hypotony, bleb leak, scarring, infection, choroidal problems, cataract | Powerful pressure reduction but requires intensive postoperative management |
| Glaucoma drainage implant | Hypotony, tube exposure, blockage, corneal damage, double vision, infection | Useful in difficult or previously operated eyes; hardware creates additional long-term risks |
| MIGS | Hyphema, temporary pressure spikes, inflammation, angle or device-related problems | Generally lower serious-complication risk but usually more modest pressure lowering |
The Bottom Line
Glaucoma surgery carries real risks, but most postoperative complications are temporary or treatable, while serious vision-threatening complications are considerably less common.
Trabeculectomy can provide powerful eye-pressure reduction but carries risks including hypotony, bleb leakage, infection, choroidal complications, cataract progression and eventual scarring of the drainage pathway.
Glaucoma drainage implants avoid some bleb-related problems but introduce device-specific risks such as tube exposure, blockage, movement, corneal damage and occasionally double vision. MIGS generally has a more favourable safety profile, although hyphema, pressure spikes and procedure-specific complications still occur, and MIGS may not lower pressure enough for every patient with advanced glaucoma.
No surgical risk should be considered in isolation. The real decision is whether the expected risk of surgery is lower than the risk of allowing glaucoma to continue damaging the optic nerve.
Most importantly: Glaucoma surgery is not chosen because it has no risks. It is chosen when lowering eye pressure offers the best chance of protecting the patient's remaining vision despite those risks.
