Saturday, July 22, 2006

Glaucoma valvular devices

The filtration devices are equipped with a tube (at the top of the photo) that protrudes from a base plate (white in the photo) with holes.
The device in the image is a Baerveldt implant. The description should be accurate and any obstruction of the tube should be noted. If there is unusual or exuberant soft tissue on part of the valve it should be submitted for sectioning.

Ahmed valves are clear plastic devices that contain a membrane type valve composed of 2 flaps that seal an opening. In the figure below an Ahmed valve is photographed face on or from above. In the overview, five holes lie at the periphery of the valve for positioning with suture and the trapezoidal valvular mechanism. The tube (missing in this picture would be at the base of the arrow and the direction of flow would follow the arrow. The inner workings of the valve are seen after longitudinally making a cross section of the trapezoidal chamber (in the plane of the red arrow). The aqueous flows from right to left in the blue colored channel (arrow 1). The leaves of the valve are relatively long and indicated by number 2. When the pressure in the anterior chamber is high, the valve leaves separate creating an open valve as depicted. When the pressure is low the leaves of the membrane have natural elasticity that keeps them together seen in the photograph below (valve closed arrow 3). It is important to examine the region of the valve carefully in case of Ahmed valve failure for evidence of fibrous tissue or obstruction of the valve.

An express shunt is a considerably more simple glaucoma filtration device. Click here.



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