⚠️ Understanding Hypotony: When Eye Pressure Drops Too Low After Glaucoma Surgery

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🟠 STORY AT A GLANCE

• Hypotony refers to abnormally low intraocular pressure (IOP), typically defined as less than 5 mmHg.

• It is a known complication of glaucoma surgery, especially procedures that increase aqueous outflow (e.g., trabeculectomy, tube shunts).

• While lowering eye pressure is the goal of glaucoma surgery, too much pressure reduction can lead to vision-threatening consequences.

• Hypotony may result in blurred vision, choroidal effusions, maculopathy, corneal folds, and even permanent vision loss.

• Prompt recognition and management are critical to preserving vision after surgery.

⚠️ Understanding Hypotony: When Eye Pressure Drops Too Low After Glaucoma Surgery

Glaucoma surgery is designed to lower intraocular pressure (IOP) and protect the optic nerve from further damage. But when the pressure drops too low, a new problem can arise—hypotony.

While the surgical goal is to reduce pressure enough to prevent vision loss from glaucoma, too much of a drop can destabilize the entire structure of the eye. In some cases, hypotony can lead to complications that are just as serious as the disease we’re trying to treat.

👁️ What Is Hypotony?

Hypotony is generally defined as an IOP of less than 5 mmHg. It is most commonly seen after:

• Trabeculectomy (traditional filtering surgery)

• Tube shunt implantation (Ahmed, Baerveldt, etc.)

• Minimally invasive glaucoma surgery (MIGS) (less commonly, but still possible)

Some degree of low pressure immediately after surgery is expected. However, when it persists or causes structural changes in the eye, it becomes pathologic and requires attention.

🔍 Signs and Symptoms of Hypotony

Patients may experience:

• Blurry or distorted vision

• Visual fluctuations

• Ocular discomfort or ache

• Vision loss (if complications progress)

Your doctor may observe:

• Shallow or flat anterior chamber

• Choroidal effusions or detachments

• Corneal striae or folds

• Macular changes (hypotony maculopathy)

🧬 What Causes Hypotony?

In glaucoma surgery, hypotony typically results from excessive aqueous outflow—when too much fluid leaves the eye too quickly. Specific causes may include:

• Overfiltration in a trabeculectomy bleb

• Leaking scleral or conjunctival wounds

• Over-functioning tube shunts without flow resistance

• Delayed healing or wound dehiscence

• Use of antimetabolites (e.g., mitomycin-C) that reduce scarring but increase filtration risk

🛠️ How Do We Treat Hypotony?

Treatment depends on the severity and cause: