Aqueous shunts are microsurgical drainage devices that help control the intraocular eye pressure (IOP) in glaucoma by creating a new drainage channel for the eye which results in a small blister or bleb behind the eyelid. Reducing the pressure on the optic nerve in this manner prevents further damage and further loss of vision in glaucoma.
Please note that control of the eye pressure with an aqueous shunt will not restore vision already lost from glaucoma.
There are many implants that can be used but the most common ones are Baerveldt implant, the Molten implant and the Ahmed glaucoma valve. They all consist of a small tube that takes the fluid from inside the eye (aqueous humour) to a plate underneath the outer coat of the eye (conjunctiva). The tube and bleb are mostly hidden under the eyelid.
Although all shunts perform approximately the same function, there are important differences that affect the eye pressure in the first few weeks after surgery and other differences that influence the healing of the eye around the shunt and the long-term eye pressure.
The Ahmed Glaucoma Valve contains a type of valve that helps to prevent very low eye pressure during the first few weeks after surgery. The Baerveldt and Molteno implants do not contain valves but do have other advantages. Because the Baerveldt and Molteno implants have no valve, they must be blocked with a stitch that is either tied around the outside of the silicone tube (external ligature), or threaded through the inside of the tube (occluding suture) at the time of surgery. The purpose of the stitches is to prevent the shunt from draining excessively in the first few weeks after surgery and causing the eye pressure to be too low.