Surgical Techniques

The glaucoma drainage devices were all placed with a similar technique in the chosen quadrant, with modifications when glaucoma drainage device replacement in the same location was being performed. After a lid speculum was placed in the eye, a traction suture was placed to expose the quadrant in question. A fornix incision through conjunctiva and Tenon capsule was made approximately 8 mm from the limbus in the area between the rectus muscles. In cases of repeat surgery, care was taken to preserve both conjunctival and Tenon layers for later double-layer closure. For initial glaucoma drainage devices, or if the tube location was to be altered with the replacement glaucoma drainage device, blunt dissection was then carried out to the limbus anteriorly, and posteriorly between the respective rectus muscles.

For replacement glaucoma drainage devices, the tubing was generally exposed behind the sclera patch graft and carefully unroofed, and then was completely ligated just in front of the plate, with a 6-0 Vicryl suture (Ethicon, Inc., Somerville, New Jersey, USA), which was also attached to nearby Tenon or scar tissue as an anchor. The tube was then cut separate from the plate to allow its removal without pulling the tubing from the eye unintentionally. For new glaucoma drainage devices, blunt dissection was then carried out between the 2 respective rectus muscles. For replacement glaucoma drainage devices, the plate was then exposed by penetrating the capsule, with care taken to inspect the valve chamber and to identify any tissue that might be entering the chamber from the capsule tissue. Most of the capsule was then removed anteriorly, transecting tissue that spanned the holes in the plates of the Baerveldt and Ahmed flexible plate reservoirs; the plates were then removed. Ahmed plates were further inspected to identify fibrovascular tissue within the valve chamber, although sometimes the tissue was clearly removed during the process of capsule penetration and plate removal described above. When a larger plate was intended to be placed, the lateral and posterior “walls” of the capsule were also carefully opened, and sometimes partially removed, with care taken to identify the adjacent rectus muscles and to avoid injuring them.

For the Baerveldt devices, the 2 rectus muscles in that quadrant were hooked. Next, the Baerveldt device was inspected and the tube was flushed to ensure patency. A 6-0 Vicryl suture was then placed across the tube near the plate in order to completely ligate the tube. The Baerveldt device was then placed into the chosen quadrant with the wings tucked under the 2 rectus muscles. For replacement Baerveldt devices, the plate was often trimmed so that the wings were blunted, making it easier to place the plate where the prior glaucoma drainage device reservoir had been located. An 8-0 nylon suture was used to secure the plate to the sclera. The tube was then trimmed to an appropriate length with a bevel upward for tubes placed in the anterior chamber and sulcus, and a bevel downward for tubes placed pars plana.

For initial Baerveldt tube placement, a 30 gauge needle was then inserted at the intended site of tube placement (anterior chamber, sulcus, or pars plana). Once the needle was noted to be in the correct position, the 30 gauge needle was removed and replaced by a 23 gauge needle to create a large enough opening for the tube to be placed with the tube introducer. After the tube was noted to be in the correct position, it was secured with a 9-0 nylon suture to the globe. Three venting slits were then placed in the tubing just anterior to the ligation suture, except in cases where early hypotony was to be avoided (eg, Sturge-Weber-associated glaucoma). For replacement Baerveldt devices, the tubing was advanced into the “sleeve” of the prior glaucoma drainage device tube, after removing the tubing of the prior device from its location in the anterior chamber, sulcus, or pars plana.

For the Ahmed devices, the procedure was identical to that described above, except that no tube ligation was carried out, and the insertion of the reservoir was carried out with care not to compress the valve chamber at any time. The tube was then placed in a manner identical to that for the Baerveldt devices, whether a primary or a replacement Ahmed device was being placed.

After placement of the glaucoma drainage device, donor sclera or cornea was the used to cover the site of tube entry into the globe. For replacement glaucoma drainage devices, donor tissue was sometimes not required as the initial patch material was still in place. The Tenon capsule and conjunctiva were then closed separately with running 8-0 Vicryl sutures on a vascular needle to ensure a watertight closure.

Results are reported as mean (standard deviation) unless otherwise noted. Statistical comparisons were performed using a 2-tailed t test for continuous variables, the χ ² test for ratios, and Kaplan-Meier survival curve analysis for surgical success. P values are considered significant if ≤ .05.