Intraocular pressure (IOP) refers to the fluid pressure inside the eye, which is maintained by a continuous flow of a clear liquid called aqueous humor. This fluid nourishes the eye’s structures and helps the eye maintain its shape. When the balance between aqueous humor production and drainage is disrupted, IOP can rise, potentially leading to damage within the eye. For individuals with persistently elevated IOP that cannot be managed by other means, an aqueous shunt may be considered as a medical device to help regulate this pressure.
Understanding Glaucoma and Eye Pressure
Glaucoma is a group of eye conditions that damage the optic nerve. This damage often occurs due to increased intraocular pressure, although some forms of glaucoma can develop even with normal eye pressure. The eye constantly produces aqueous humor, a fluid that flows from behind the iris, through the pupil, and into the anterior chamber. From there, it typically drains out of the eye through a sieve-like tissue called the trabecular meshwork, located at the angle where the iris and cornea meet.
When this drainage system becomes blocked or functions improperly, aqueous humor accumulates, causing the pressure inside the eye to rise. This sustained high pressure can gradually damage optic nerve fibers, leading to blind spots and, if untreated, vision loss or blindness. Glaucoma is often called the “silent thief of sight” because vision loss usually progresses slowly and painlessly, with peripheral vision often affected first, making early detection challenging.
What is an Aqueous Shunt?
An aqueous shunt is a small, implantable medical device designed to create an alternative pathway for the drainage of aqueous humor from the eye. These devices are also known as tube implants, glaucoma drainage devices, or glaucoma tube shunts. Each shunt consists of two main components: a tiny silicone tube and a larger plate or reservoir.
An aqueous shunt bypasses the eye’s natural, impaired drainage system, lowering intraocular pressure. There are different types of aqueous shunts, broadly categorized as valved or non-valved devices. Common examples include the valved Ahmed Glaucoma Valve, and non-valved devices like the Baerveldt Glaucoma Implant and Molteno Implant. The type of valve influences how the device functions, particularly in the immediate post-surgical period.
How an Aqueous Shunt Works
An aqueous shunt lowers eye pressure by diverting aqueous humor away from compromised natural drainage pathways. The small silicone tube of the shunt is inserted into the anterior chamber of the eye. This tube collects aqueous humor from inside the eye.
The collected fluid then travels through the tube to the plate or reservoir component of the shunt. This plate is positioned on the sclera (white part of the eye) and covered by the conjunctiva. As the aqueous humor collects over the plate, it forms a small, fluid-filled blister or “bleb” under the conjunctiva. The fluid within this bleb is absorbed by surrounding blood vessels and the lymphatic system, reducing intraocular pressure.
The Surgical Procedure and Recovery
Aqueous shunt implantation surgery is typically an outpatient procedure, allowing patients to go home the same day or the day after. The surgery usually lasts between one and two hours and can be done under local or general anesthesia. After the procedure, the eye will likely be red and swollen, and the eyelid may droop temporarily, resolving over several weeks to months.
Patients are given antibiotic and steroid eye drops to prevent infection and reduce inflammation. A plastic shield may need to be worn at night to protect the eye from accidental rubbing. Strenuous activity, bending, and swimming should be avoided, but activities like reading and watching television are safe. Follow-up appointments with the ophthalmologist are scheduled frequently to monitor healing and shunt function.
Managing Eye Pressure After Shunt Placement
The long-term goal of aqueous shunt placement is to achieve sustained reduction of intraocular pressure, which helps prevent optic nerve damage and vision loss. While the shunt is a permanent solution, ongoing monitoring by an ophthalmologist is necessary to ensure its effectiveness. Pressure control with a shunt does not restore vision already lost from glaucoma, but it can help preserve remaining vision.
Even after shunt implantation, some patients may still require glaucoma eye drops to maintain optimal pressure. Intraocular pressure can fluctuate after surgery, and a temporary rise in pressure, known as the hypertensive phase, can occur in the first few months. Additional interventions, such as laser treatment to a stitch around the tube or adjustments to the shunt, may be needed to achieve target pressure levels.