Where could a glaucoma shunt fit in clinical practice?

The resistance mechanism consists of an intrinsic fixed part in the device's design, which restricts the flow through reduction/constriction of the lumen. Based on the physical principle (Hagen-Poiseuille equation) the pressure drop along the tube is directly proportional to the fluid viscosity (M), the tube length (L), and flow rate (Q), and is inversely proportional to the fourth power of tube diameter. Three openings at the proximal end create an alternative conduit for aqueous humour drainage in case of occlusion of the primary (axial) opening by the iris.

We feel that implantation is a straightforward procedure. We have found that it is best to create a limbal based scleral flap (5 x 5 mm) and then to apply Mitomycin C (MMC) using a soaked sponge (soak and dry technique). The device can then be inserted into the anterior chamber using a 25/23-gauge needle.

This procedure is indicated for a number of glaucoma types, including primary open-angle glaucoma (POAG), neovascular glaucoma, combined cataract/glaucoma surgery, post-traumatic glaucoma and congenital glaucomas that, because of anatomic anomalies, cannot be subjected to standard surgery.

Evaluating safety & efficacy

We conducted a study to evaluate the efficacy and safety of implanting the Ex-PRESS shunt under a scleral flap with MMC application. The case series included 16 eyes, 11 with uncontrolled glaucoma and five with neovascular glaucoma. Measurements included pre and postoperative IOP with applanation and pre- and postoperative best corrected visual acuity (BCVA).

Subjects underwent surgery with local anaesthesia (topical oxybuprocaine 0.4% and parabulbar anaesthesia with naropine 1% and xylocaine 2%). Postsurgery, patients were treated with topical antibiotics (ofloxacin four times a day) and steroids (dexamethasone 0.2% four times a day) for fifteen days. IOP was measured on the first day postsurgery and at one week, one month and three months postoperatively.