Mechanism of Action
Plate-based tube implants are designed to shunt aqueous from the anterior chamber to a space-maintaining plate in the equatorial subconjunctival space. Broadly speaking, plate-based tube implants can be divided into valved and nonvalved types. The Ahmed Glaucoma Valve (New World Medical; Video 13-8) has 2 leaflets in the plate that are designed to separate when the IOP is above a certain level (approximately 8–12 mm Hg). When the pressure is lower, the leaflets come together, preventing flow through the tube. The nonvalved Baerveldt (Johnson & Johnson Vision Care, Inc.; Video 13-9) and Molteno (Molteno Ophthalmic Limited) implants have no restriction to flow from the tube to the plate.
Ahmed valve implantation.
Courtesy of Simon K. Law, MD, PharmD.
Baerveldt tube shunt implantation.
Courtesy of JoAnn A. Giaconi, MD.
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.