Glaucoma is a serious eye condition characterized by progressive damage to the optic nerve, which transmits visual information from the eye to the brain. This damage is often related to elevated intraocular pressure (IOP), caused by an imbalance in the production and drainage of the eye’s internal fluid, known as aqueous humor. Treatment typically begins with prescription eye drops designed to lower this pressure. However, when medication is insufficient to control IOP and prevent further vision loss, surgical intervention becomes necessary to preserve remaining sight.
Understanding Glaucoma Drainage Implants
When standard treatments, such as eye drops or initial surgeries like trabeculectomy, fail to adequately reduce eye pressure, a Glaucoma Drainage Device (GDD), often called a tube shunt, may be recommended. These implants create an alternative pathway for aqueous humor to exit the eye by directing fluid from the anterior chamber to an external reservoir on the eye’s surface.
The Baerveldt Glaucoma Implant (BGI) is a common GDD consisting of a small silicone tube connected to a large, flexible silicone plate. This design is classified as non-valved, meaning it does not have a mechanical flow-restrictor built into the tube. The BGI is known for its large plate size (e.g., 250 mm² or 350 mm²), which maximizes the area for fluid absorption.
BGI is indicated for complex cases of glaucoma, including those with extensive scarring from prior surgeries, neovascular glaucoma, or inflammatory glaucomas. The large surface area helps achieve lower long-term intraocular pressure. The aqueous humor shunts to the plate, collecting beneath the conjunctiva where it forms a blister-like structure called a bleb. This fluid then diffuses into local blood vessels, lowering the pressure inside the eye.
The Surgical Procedure
The BGI procedure is typically performed under local anesthesia with sedation, ensuring the patient is comfortable. The surgeon makes a small incision in the conjunctiva to access the sclera (the white outer layer of the eye). The large silicone plate is then secured to the surface of the eye, usually in the upper-outer quadrant, hidden beneath the upper eyelid.
The plate is positioned beneath the conjunctiva and Tenon’s capsule, often anchored between two adjacent rectus muscles. The silicone tube attached to the plate is threaded forward and inserted into the anterior chamber through a small opening in the sclera. A tissue patch graft, often donor material, is placed over the tube where it enters the eye to prevent erosion through the overlying tissue.
A necessary step for the non-valved BGI is the temporary ligation or occlusion of the tube. This involves tying a dissolvable or removable suture around the tube to temporarily block the flow of aqueous humor. This temporary blockage prevents a rapid drop in eye pressure immediately after surgery, known as hypotony. The ligation allows time for a protective fibrous capsule (bleb) to form around the drainage plate, which provides the resistance needed to regulate long-term fluid flow.
Post-Operative Recovery and Care
Following surgery, patients should expect some discomfort, redness, and blurred vision. A protective eye patch is often worn overnight, and a schedule of topical medications is prescribed to manage inflammation and prevent infection. This regimen typically includes antibiotic and steroid eye drops used for several weeks or months.
Follow-up appointments are frequent and closely spaced, particularly in the first few weeks, to monitor eye pressure and the healing process. During this initial phase, the temporary ligation keeps the tube closed, and eye pressure may remain high, sometimes requiring continued use of pre-operative glaucoma drops. This “healing phase” allows the body to form the fibrous capsule around the plate, which is necessary for long-term pressure control.
The implant begins to function fully when the temporary ligation dissolves or is released, typically between four to eight weeks post-surgery. If a dissolvable suture (like Vicryl) was used, it absorbs naturally; if a non-dissolvable suture was used, it might be released in the clinic using a laser. This tube opening marks a transition where the eye pressure should begin to drop significantly. Patients must avoid strenuous activities like heavy lifting, bending over, or contact sports for at least four weeks.
Outcomes and Potential Risks
The long-term goal of BGI surgery is to achieve stable, lower intraocular pressure that prevents further damage to the optic nerve. Studies show that BGI can be highly effective in controlling IOP, with success defined as maintaining pressure within a safe range without the need for additional surgical intervention. Many patients still require some glaucoma medication after the implant to reach their target pressure, though the number of drops is often reduced.
The Baerveldt implant carries specific long-term risks. One potential complication is hypotony, where the eye pressure drops too low, leading to vision issues or structural problems. This risk is managed initially by the temporary ligation, but hypotony can occur if the fibrous capsule around the plate forms too thin or weak.
Other risks involve the physical components of the implant. These include tube erosion, where the tube becomes exposed on the surface of the eye through the overlying conjunctiva. Diplopia, or persistent double vision, can occur if the plate interferes with the movement of the eye muscles. Additionally, the fibrous capsule can sometimes become too thick, leading to failure of the implant to adequately lower pressure over time.