The Ahmed Glaucoma Valve (AGV) is a medical shunt used in the treatment of glaucoma to reduce & control intraocular pressure (IOP), and reducing drug use. The AGV is effective in all types of glaucoma due to its unique valve system. Exhibiting a level of control only a true valve can offer.
Mechanism: The device works by bypassing the trabecular meshwork and redirecting the outflow of aqueous humor through a small tube into an outlet chamber or bleb. The IOP generally decreases from around 33 to 10 mmHg by removing aqueous on average 2.75 microliters/ min.
Types:
There are also several different glaucoma drainage implants. These include the original Molteno implant (1966), the Baerveldt tube shunt, or the valved implants, such as the Ahmed glaucoma valve implant and the later generation pressure ridge Molteno implants. The flow tube is inserted into the anterior chamber of the eye and the plate is implanted underneath the conjunctiva to allow flow of aqueous fluid out of the eye into a chamber called a bleb. Ahmed Valve itself have many types in order to fit all patients from young infant to adults.
Indications:
The glaucoma valve implant is indicated for glaucoma patients not responding to maximal medical therapy, with previous failed guarded filtering surgery (trabeculectomy) or in cases where conventional drainage surgery is unlikely to succeed. Common situations where the use of a glaucoma implant as a primary procedure is indicated include:- • Neovascular glaucoma -- glaucoma associated with vascular disease of the eye (often diabetes). • ases of Uveitis -- acute or chronic inflammation of the eye. • Traumatic glaucoma -- glaucoma associated with injury to the eye. • Silicone glaucoma -- glaucoma due to Silicone used to repair a detached retina. • Infantile/Juvenile glaucoma -- often associated with developmental defects of the eye.
Surgical technique:
The flow tube is inserted into the anterior chamber of the eye and the plate is implanted underneath the conjunctiva to allow flow of aqueous fluid out of the eye. • The first-generation Molteno and other non-valved implants sometimes require the ligation of the tube until the bleb formed is mildly fibrosed and water-tight, this is done to reduce postoperative hypotony -- sudden drops in postoperative intraocular pressure (IOP). • Valved implants such as the Ahmed glaucoma valve attempt to control postoperative hypotony by using a mechanical valve. Studies show that in severe cases of glaucoma, double plate Molteno implants are associated with lower mean IOP in the long term compared to the Ahmed glaucoma valve.
Complications:
The ongoing scarring over the conjunctival dissipation segment of the shunt may become too thick for the aqueous humor to filter through. This may require preventive measures using anti-fibrotic medication like 5-fluorouracil (5-FU) or mitomycin-C (during the procedure), or creating a necessity for additional surgery.
