A Comprehensive Guide to What are the Side Effects of the Ahmed Glaucoma Valve?

October 10, 2025 •

3 min read

The implantation of an Ahmed glaucoma valve is an effective surgical technique for reducing intraocular pressure (IOP) in patients with refractory glaucoma. However, like any surgical procedure, it is associated with a range of potential side effects and complications that patients should be aware of, both in the immediate postoperative period and in the long term.

Quick Summary

This article details the potential side effects and complications of Ahmed glaucoma valve implantation, including early risks like transient hypotony and hyphema, and later issues such as bleb encapsulation, tube exposure, and diplopia. It also discusses comparisons with other implants and potential management strategies.

Key Points

Transient Hypotony: Many patients experience temporary low intraocular pressure (IOP) shortly after surgery, which typically resolves as the implant site heals.
Hypertensive Phase: A common reaction to the implant is a period of elevated IOP weeks or months after surgery, caused by fibrous encapsulation around the plate.
Encapsulated Bleb: A long-term complication where the scar tissue around the valve plate hardens, restricting aqueous flow and causing treatment failure.
Tube Exposure: In rare but serious cases, the drainage tube can erode through the surface of the eye, presenting a significant risk of infection.
Corneal Damage: The presence of the tube in the anterior chamber can lead to a decrease in corneal cell density over time, potentially causing corneal edema.
Double Vision: Restrictive strabismus caused by the implant can lead to diplopia, which may be temporary or persistent.
Serious Complications: While rare, severe events like endophthalmitis, retinal detachment, or significant hemorrhage can occur and require urgent medical intervention.

Early Postoperative Complications

During the initial weeks following Ahmed glaucoma valve (AGV) implantation, several complications may arise. These are typically monitored closely by the ophthalmologist and often resolve on their own.

Hypotony

Ocular hypotony, or abnormally low intraocular pressure (IOP), is a potential early side effect, despite the AGV's design to minimize this risk. A study published in 2023 noted that 16.3% of eyes experienced early postoperative hypotony, typically defined as an IOP of 6 mmHg or less. Possible causes include over-priming the valve during surgery or leakage. Most cases of transient hypotony resolve spontaneously as the implant site heals. For severe or persistent cases, surgical intervention may be necessary.

Hyphema and Hemorrhage

A common early complication is hyphema, blood in the anterior chamber, occurring in 12.6% of patients in a 2023 study. Vitreous hemorrhage is another possible issue. Hemorrhages usually resolve over time, but monitoring is crucial. Severe hemorrhages, such as suprachoroidal hemorrhage, are a rare but serious risk.

Other Early Risks

Choroidal Effusions: Fluid buildup in the choroid, often resolving without intervention.
Shallow Anterior Chamber: May require temporary measures to deepen the chamber.
Tube Occlusion: Blockage of the tube by blood clots, iris, or vitreous humor.

Long-Term Complications

Several side effects can manifest months or years after AGV surgery.

Hypertensive Phase and Encapsulated Bleb

Capsular fibrosis, scar tissue around the valve plate, causes a 'hypertensive phase,' an increase in IOP typically peaking one to two months after surgery. This can restrict aqueous humor flow, making the implant less effective. If IOP remains elevated, the bleb is encapsulated. Surgical revision may be needed to restore outflow.

Tube Exposure and Endophthalmitis

Tube exposure is a serious late-term complication where the tube erodes through the conjunctiva. This creates a pathway for bacteria, increasing the risk of endophthalmitis, a severe infection. Surgical repair is necessary to cover the exposed tube.

Corneal Complications

The tube in the anterior chamber can affect the corneal endothelium, potentially leading to corneal edema. Long-term corneal issues can lead to vision loss, and in severe cases, a corneal transplant may be required. Correct tube positioning is crucial.

Diplopia (Double Vision)

Diplopia can result from restrictive strabismus caused by the implant plate or from inflammation. While some cases are transient, others may be persistent and require surgical correction. The Ahmed-Baerveldt Comparison (ABC) study found a persistent diplopia rate of around 12% for AGV patients.

Comparison: Ahmed vs. Baerveldt Implants

Clinical trials have compared Ahmed glaucoma valves with Baerveldt glaucoma implants. The AGV is designed to prevent hypotony with its valve, while the Baerveldt relies on fibrosis to regulate flow, potentially leading to higher early complication rates.


Feature	Ahmed Glaucoma Valve (AGV)	Baerveldt Glaucoma Implant (BGI)
Mechanism	Restrictive, flow-limiting valve	Non-valved; relies on surgical occlusion and fibrous encapsulation for flow control
Hypotony Risk	Lower incidence, especially early on, due to the valve mechanism	Higher risk of early, significant hypotony; often requires surgical occlusion
Post-Op IOP	Generally produces good IOP control, but may be slightly higher long-term	Tends to achieve slightly lower long-term IOP levels
Hypertensive Phase	Common occurrence; managed with medications or needling	Also occurs, but often later than AGV
Long-Term Efficacy	Satisfactory, but requires more long-term medication use compared to BGI	Superior in reducing long-term medication dependence
Serious Complications	Fewer serious complications reported in some studies compared to BGI, especially early on	Higher rates of serious early complications like hypotony-related vision loss

Conclusion: Managing Post-Surgical Risks

The Ahmed glaucoma valve is a crucial tool for managing refractory glaucoma, and its valved mechanism helps mitigate the risk of early hypotony. Patients should be aware of the potential for a hypertensive phase caused by fibrotic encapsulation, which can often be managed with medication or a minor procedure. Less common but serious long-term issues include tube exposure and corneal changes. The decision to undergo AGV implantation involves weighing benefits and risks, with individual patient factors influencing the outcome. Close postoperative monitoring and potential additional treatments are expected.

Long-term results of Ahmed glaucoma valve implantation in Egyptian patients with resistant glaucoma

Frequently Asked Questions

Initial recovery often involves some discomfort and visual fluctuations for several weeks. The full stabilization of intraocular pressure and vision can take several months as the eye heals and the bleb matures.

The hypertensive phase is a period of high intraocular pressure (IOP) that occurs weeks to months after surgery due to scar tissue forming around the implant. It is managed with medications and sometimes a procedure called bleb needling to break up the scar tissue.

A temporary period of low eye pressure (hypotony) is a known early side effect and often resolves on its own. However, persistent or severe hypotony should be evaluated by your ophthalmologist.

Yes, the valve can fail over time, most commonly due to excessive capsule fibrosis (encapsulated bleb) that blocks fluid drainage. This may require further treatment or additional surgery.

You should contact your doctor immediately if you experience severe pain, redness, swelling, or eye discharge. These could be signs of a serious complication like an infection.

Tube exposure is when the implant's drainage tube erodes through the outer layer of the eye. It is a risk factor for endophthalmitis and typically requires prompt surgical repair to re-cover the tube.

Yes, the Ahmed valve's flow-limiting mechanism is specifically designed to reduce the risk of early hypotony compared to some other valveless drainage devices like the Baerveldt implant.