Type of Surgery
Information
Last updated: 02/17/2009
The function of the implant is to lower the intraocular pressure by filtering excess aqueous fluid out of the eye. During the first few weeks after surgery, a bleb of fibrous tissue and collagen forms around the plate of the implant. The formation...
of a filtration bleb is essential for filtering the excessive aqueous fluid. The thickness of the bleb, as well as the size or number of plates, determines the rate at which aqueous flows out of the anterior chamber of the eye. The excess aqueous fluid is shunted through the tubing of the implant, and passes through the space that develops between the bleb and the plate. By diffusion, the fluid flows into the capillaries where it exits the eye and enters general circulation. The IOP is lowered as a result of this decrease in fluid.
There are various types of implants used in glaucoma surgery. They fall into two categories: the non-valved (free flow implants) and valved (resisted-flow implants). One of the first free-flow implants was the Molteno implant, which consists of one or two polypropylene reservoirs connected to a silicone tube. The non-valved Baerveldt implant is larger than the Molteno, and is available in three sizes.
The restrictive implants, which include the Krupin and Ahmed implant, have valves that automatically close if the intraocular pressure is too low. This is important because in the first few weeks after surgery (before the bleb forms), the aqueous fluid can flow unimpeded through the implant. As a result, hypotony (low level of fluid in the eye) can develop.
Newer implants such as the Express shunt and the Gore-Tex tube shunt are in early stages of use.
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Tube-shunt surgery, or Seton tube shunt glaucoma surgery, is a surgical method to treat glaucoma. Glaucoma is a potentially blinding disease affecting 2–3% of the United States population. The major known cause of glaucoma is a relative increase in intraocular pressure, or IOP. The purpose of glaucoma treatment, whether medical or surgical, is to lower the IOP.
Aqueous fluid is made continuously, and circulates throughout the eye before draining though channels in the eye's anterior chamber. When too much fluid is made, or it is not drained sufficiently, the IOP rises. This fluid build-up can lead to glaucoma. Normal intraocular pressure is under 21 mm/Hg. Glaucoma develops at IOPs higher than 21mm/Hg. However, approximately 20% of glaucoma patients never have pressures higher than 21 mm/Hg.
From http://www.surgeryencyclopedia.com/St-Wr/Tube-Shunt-Surgery.html
Other Information
Approximately 56% of all patients achieve results of 20/20 or better and over 90% achieve 20/40 or better (which is good enough to drive without corrective lenses in most regions).1 Those with moderate to high myopia (greater than 7 diopters) have a lesser chance of achieving that result. As technique and technology improve, the results continue to improve.
From: Eye Surgery Education Council
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