Glaucoma Valve or Tube Shunt
A glaucoma valve or tube shunt is a medical device used in the treatment of glaucoma, a condition that causes increased intra-ocular pressure (IOP) in the eye, leading to potential vision loss. These devices help to reduce eye pressure by facilitating the drainage of excess aqueous humor (fluid inside the eye) to an external reservoir or the outside of the eye. Glaucoma valves or tubes are typically used when medications and less invasive surgical procedures like trabeculectomy have failed to control intra-ocular pressure (IOP) adequately. These devices are most commonly used for complex or refractory glaucoma cases, including: Neovascular glaucoma, Uveitic glaucoma, Congenital glaucoma, Patients who have failed previous glaucoma surgeries.
How it works:
A glaucoma valve or tube consists of two main components:
Tube: A small tube is inserted into the anterior chamber of the eye (just inside the cornea) or sometimes into the vitreous cavity or posterior chamber, depending on the case.
Plate/ Reservoir: The tube is connected to a plate that is typically placed beneath the conjunctiva (the thin outer membrane of the eye). This plate acts as a reservoir to collect fluid.
The device regulates the outflow of aqueous humor from the eye to reduce intraocular pressure. The fluid flows through the tube to the plate, where it is absorbed by surrounding tissues or drained away. The "valve" in some types of these devices regulates the flow of fluid, preventing hypotony (excessively low IOP) by controlling the rate at which the fluid leaves the eye.
Types of Glaucoma Valves:
Ahmed Glaucoma Valve (AGV): This is one of the most commonly used devices. It has a built-in valve that allows fluid to exit when the pressure reaches a certain threshold, preventing over-drainage.
Baerveldt Glaucoma Implant: This device doesn't have a valve, so it may initially require a temporary ligature or stent to prevent over-drainage until the body forms a fibrous capsule around the plate.
Molteno Implant: One of the earlier designs, it allows for the gradual reduction of IOP but does not have a built-in valve like the Ahmed.
Procedure:
The surgery is usually performed under local or general anesthesia, and involves:
Creating a small incision in the conjunctiva to implant the plate of the device.
Inserting the tube into the anterior chamber of the eye.
Securing the plate and ensuring proper flow of aqueous humor.
Risks and Complications:
Although effective, glaucoma valve or tube shunt surgery carries certain risks:
Hypotony (too low IOP)
Tube exposure or erosion
Infection (endophthalmitis)
Diplopia (double vision)
Corneal damage from tube contact
Fibrosis around the plate, which may reduce the device’s effectiveness over time
Postoperative Care:
Patients require close monitoring after surgery to ensure that the device is functioning properly and that IOP remains within a safe range. They may be prescribed medications to manage inflammation, prevent infection, or control the pressure.
This intervention is considered when more conservative approaches don't work, and it often plays a vital role in preventing further damage to the optic nerve and preserving remaining vision in advanced glaucoma cases.
