Glaucoma surgery can lower pressure inside the eye and help protect the remaining vision when medicines or laser treatment are not providing enough control. But like any operation, glaucoma surgery can cause side effects and complications.
*AI-generated image - for illustration only. Clinical accuracy is not guaranteed.
Some effects—such as temporary blurred vision, mild soreness, watering and a gritty sensation—are common during healing and usually improve. Other problems, including very low eye pressure, infection, significant bleeding or sudden loss of vision, require prompt medical attention.
The exact risks depend on which operation you have. Trabeculectomy, glaucoma drainage implants and minimally invasive glaucoma surgery (MIGS) do not have identical side-effect profiles.
For an overview of the different procedures, see our main guide to Glaucoma Surgery.
What Side Effects Are Normal After Glaucoma Surgery?
Immediately after surgery, the operated eye will not necessarily feel or see completely normal. Temporary effects can include:
- Blurred vision
- Mild soreness or aching
- A gritty or scratchy feeling
- Watering
- Mild redness
- Light sensitivity
- Temporary swelling around the eye
Blurred vision is particularly common after traditional glaucoma surgery. It may improve within the first week or two, although some patients take several weeks before their vision settles. The eye can also feel as though something is inside it because of the incision, stitches, inflammation or changes occurring while the tissues heal. Mild discomfort is expected. Severe or progressively worsening pain is not.
*AI-generated image - for illustration only. Clinical accuracy is not guaranteed.
Side Effect or Complication: What Is the Difference?
A temporary side effect usually occurs as part of normal recovery and gradually improves. A complication is a problem caused by surgery or healing that may require additional treatment.
| Often Part of Early Recovery | Needs Medical Assessment |
|---|---|
| Mild soreness | Severe or increasing pain |
| Temporary blurred vision | Sudden or rapidly worsening vision |
| Mild watering | Sticky discharge with increasing redness |
| Gritty sensation | Marked eye swelling or intense discomfort |
| Mild redness | Increasing redness with pain or reduced vision |
1. Blurred Vision After Glaucoma Surgery
Temporary blurred vision is common. It may occur because of:
- Inflammation after surgery
- Temporary changes in eye pressure
- Corneal swelling
- Eye drops
- Changes in the shape or focusing of the eye during healing
With trabeculectomy, vision may remain blurred for several weeks before stabilising. However, a sudden major reduction in vision—especially when accompanied by pain or redness—should not simply be assumed to be part of normal recovery.
2. Eye Pressure That Becomes Too Low
One important complication of glaucoma surgery is hypotony, meaning the pressure inside the eye becomes too low. This is particularly relevant after filtering procedures such as trabeculectomy. Low pressure may develop when fluid drains from the eye faster than intended.
Mild early hypotony may resolve as the eye heals, but significant or persistent hypotony can cause:
- Blurred or reduced vision
- Changes in the front of the eye
- Fluid collecting behind the retina or choroid
- Folds or changes affecting the macula
Some cases require adjustment of stitches, medication changes or another procedure.
3. Eye Pressure That Remains Too High
Glaucoma surgery is performed to lower pressure, but pressure can temporarily rise after the operation. Possible reasons include:
- Inflammation
- Blood temporarily blocking drainage
- Scar tissue
- A drainage pathway that is not functioning adequately
- Temporary changes related to a drainage implant
Doctors monitor eye pressure closely after surgery because both very high and very low pressure can affect vision. Treatment may involve glaucoma drops, adjusting the surgical drainage pathway or performing another procedure.
4. Bleeding Inside the Eye
A small amount of bleeding at the front of the eye is known as a hyphema. This can occur after several glaucoma procedures, particularly operations that involve the eye's drainage angle. Small hyphemas often clear without permanent problems.
More significant bleeding is much less common and may require closer monitoring or treatment. A rare but more serious complication is bleeding deeper inside the eye, such as a suprachoroidal hemorrhage. This can threaten vision and requires urgent specialist management.
5. Infection
Infection is an uncommon but important complication of glaucoma surgery. An infection affecting the inside of the eye is known as endophthalmitis and can cause permanent vision loss if not treated quickly. Warning signs can include:
- Increasing eye pain
- Increasing redness
- Rapidly worsening vision
- Marked light sensitivity
- Abnormal discharge
After trabeculectomy, infection can occasionally occur long after the initial operation because the surgery creates a permanent drainage area known as a bleb. A painful, red eye with worsening vision after previous glaucoma filtering surgery should therefore always be taken seriously—even if the operation was performed months or years earlier.
*AI-generated image - for illustration only. Clinical accuracy is not guaranteed.
6. Scarring and Failure of the Drainage Pathway
Healing is necessary after any operation, but too much healing can work against glaucoma surgery. After trabeculectomy, scar tissue can form around the new drainage pathway and prevent fluid from leaving the eye adequately. The pressure may then rise again. This is why follow-up after trabeculectomy is particularly intensive.
The ophthalmologist may use:
- Anti-inflammatory eye drops
- Anti-scarring medication
- Adjustment or removal of stitches
- Small injections around the drainage area
- Procedures to revise the bleb
7. Cataract Development or Progression
Traditional glaucoma surgery can be associated with cataract progression. A cataract occurs when the natural lens of the eye becomes cloudy. Symptoms may include:
- Increasingly blurred vision
- Glare
- Difficulty seeing in dim light
- Colours appearing less bright
Cataract is treatable with cataract surgery if it becomes visually significant. It is also important to remember that many people undergoing glaucoma surgery are already in an age group where cataracts commonly develop, so not every cataract appearing afterward is solely caused by the glaucoma operation.
8. Corneal Problems
The cornea is the clear front surface of the eye. Glaucoma surgery can occasionally cause corneal swelling or damage. This risk is particularly relevant when a glaucoma drainage tube is placed close to the cornea. Corneal problems can cause:
- Blurred vision
- Glare
- Discomfort
9. Side Effects of Glaucoma Drainage Implant Surgery
Tube shunt surgery uses a small tube attached to a drainage plate to redirect fluid from inside the eye. Possible complications include:
- Temporary high or low eye pressure
- Bleeding
- Inflammation
- Corneal problems
- Double vision in some patients
- Tube blockage or movement
- Exposure of the tube through the tissue covering it
- Infection
Tube exposure is uncommon but important. If tissue covering the tube breaks down, the tube can become exposed to the surface of the eye. This increases the risk of infection and generally requires ophthalmic assessment and treatment.
Can a Glaucoma Drainage Implant Cause Double Vision?
Yes, although it does not happen to everyone. A drainage implant sits on the outer surface of the eye beneath the surrounding tissues. In some patients, the implant or scar tissue around it can affect normal eye movement and cause diplopia, or double vision. The risk varies according to the implant and individual anatomy.
10. MIGS Side Effects
Minimally invasive glaucoma surgery (MIGS) was developed partly to provide pressure reduction with a lower risk of serious complications than traditional filtering operations. MIGS generally has a more favourable safety profile and faster recovery. However, “minimally invasive” does not mean completely risk-free.
Depending on the specific MIGS procedure, possible complications can include:
- Small amounts of bleeding in the front of the eye
- Temporary eye-pressure spikes
- Inflammation
- Temporary blurred vision
- Corneal swelling
- Scarring within the drainage angle
- Insufficient pressure reduction
Less common complications vary considerably between different MIGS techniques. This is why it is more useful to discuss the risks of the specific MIGS procedure being considered rather than asking about the risks of MIGS as though it were one operation.
The Bottom Line
Most patients experience some temporary side effects after glaucoma surgery, but serious complications are much less common. Blurred vision, mild soreness, watering, grittiness and some redness can occur during normal recovery.
More important complications include eye pressure that becomes too high or too low, bleeding, infection, cataract progression, corneal problems and failure of the drainage pathway because of scarring. Trabeculectomy generally provides powerful eye-pressure reduction but requires close postoperative monitoring and carries risks such as hypotony, bleb-related problems and scarring.
Glaucoma drainage implants have their own risks, including tube exposure, corneal problems and double vision in some patients. MIGS generally has fewer serious complications and faster recovery, although it usually produces less dramatic pressure reduction and still carries procedure-specific risks such as bleeding and temporary pressure spikes.
Most importantly: Glaucoma surgery is performed because the expected benefit of lowering eye pressure and protecting the remaining vision is greater than the expected surgical risk. Understanding which symptoms are part of normal healing—and which require urgent assessment—can make recovery safer and less worrying.
