T he pre-placed ripcord of a nonvalved Ahmed ClearPath (New World Medical) glaucoma tube shunt reduces the tube’s effective lumen size and limits outflow. The flow follows the Hagen-Poiseuille law. In line with this concept, a ripcord reduces the inner diameter of a tube shunt. When the polyglactin ligature opens, a sudden increase in flow rate can theoretically result in a sudden decrease in intraocular pressure. Owing to the placed ripcord, this decrease in pressure should be less pronounced, which theoretically should minimize the risk of hypotony at the time when the ligature opens. The two-step intraocular pressure reduction approach has been previously described. There is evidence regarding the degree to which a certain polypropylene suture restricts the outflow of a Baerveldt tube shunt. Both tubes, the Baerveldt and the Ahmed ClearPath tube, have an inner lumen of 300 µm. The ripcord can be removed at the slit lamp as needed through a small incision in the conjunctiva during the postoperative course to increase the flow rate of the tube.

The long end of the ripcord can be placed under the conjunctiva in the inferior fornix of the eye. Alternatively, the ripcord can be anchored to the sclera with a 10-0 nylon suture in the interpalpebral space posterior to the limbus ( Figure 1 , A). The benefit of this location is the ease of access for removal at the slit lamp; the disadvantage is frequent exposure through the conjunctiva at the tip of the polypropylene ripcord.

A. The blue 4-0 polypropylene suture is looped from the end of the tube on the plate of the Ahmed ClearPath inferior to the temporal interpalpebral space and secured to the sclera with an interrupted 10-0 nylon suture ∼2.0 mm posterior to the limbus and inferior to the sclerostomy site. B. The location where the ripcord is secured to the sclera is chosen just under the corneal patch graft (yellow arrow). The patch graft is then secured with 2 interrupted polyglactin sutures. The inferotemporal edge of the patch graft can be trimmed to enable better access to the ripcord. C. After the polyglactin sutures have resolved, the blue ripcord and the corneal patch graft are visible on examination at the slit lamp. D. The outline of the corneal patch graft is marked in green, and the ripcord in blue (solid line under the conjunctiva and dotted line where it is covered by the eyelid). For removal of the ripcord, an incision can be made adjacent to the patch graft (the area is marked in red). Therefore, an ∼1.0 mm conjunctival incision is made with Vannas scissors, followed by blunt dissection of Tenon’s membrane until the ripcord is clearly visible on the bare sclera. It can then be grasped and removed with jeweller’s forceps. The incision usually does not need to be sutured.

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