Trabeculectomy and tube shunt implantation are the most frequently performed incisional surgeries for the management of glaucoma. Historically, trabeculectomy was the preferred procedure and tube shunt implantation was reserved for refractory glaucoma at high risk for filtration failure. Over the last two decades, however, there has been a decline in the number of trabeculectomies performed with an increase in tube shunt implantation. Furthermore, the recent publication of the 5-year follow-up of the Tube Versus Trabeculectomy Study solidified the role of tube shunt surgery by suggesting that tube shunt surgery may have an advantage over trabeculectomy.
Anterior chamber placement
The conventional tube shunt surgery involved placement of the silicone tube in the anterior chamber. This position was feasible for phakic, pseudophakic and aphakic patients; however, it presented problems for patients with corneal disease, corneal grafts, shallow anterior chambers or abnormal iridocorneal angle anatomy. Overall, corneal complications with anterior chamber tube placement have been reported to be between 7% and 27%, with corneal graft failure rates reported as high as 52%. Furthermore, endothelial cell loss has been found to be progressive and increases up to 20% of preoperative levels at 2 years after tube placement in the anterior chamber. Constant and intermittent tube-cornea touch, such as during eye rubbing, blinking or squeezing and with eye movement, is one of the main causes implicated in progressive endothelial cell loss after surgery.
Pars plana placement
Combined pars plana vitrectomy and pars plana insertion of a tube shunt was first described in 1991 for patients with neovascular glaucoma. Since then, this technique has found favor in patients with closed angles, and it had been thought to decrease rates of corneal decompensation by eliminating tube-cornea contact. This, however, was not found to be the case, as corneal decompensation after pars plana tube insertion was reported to be 15.1% to 29.4% in patients with native corneas and 59% at 2 years in patients with corneal grafts.
The reason for the high rate of corneal complications is thought to be related to intraoperative stress on the endothelial cells during vitrectomy, prolonged operative time and postoperative inflammation. An additional disadvantage of pars plana tube insertion is that it requires a concurrent vitrectomy. This leads to increased surgical time and increased costs, and it complicates the logistics of scheduling surgery because it requires coordinating the surgery between a glaucoma surgeon and a vitreoretinal surgeon, who may not be available at all surgical centers. Moreover, it exposes patients to increased risk of posterior chamber complications such as tube blockage by residual vitreous, vitreous hemorrhage and retinal detachment, with studies reporting the rate of retinal detachment after pars plana tube placement to be between 2.5% and 20%.
Ciliary sulcus placement
In recent years, ciliary sulcus placement of tube shunts has gained attention. This technique can be performed only in pseudophakic or aphakic eyes; however, its advantage is that it helps to mitigate some of the complications associated with both anterior chamber and pars plana tube placement. By placing the silicone tube behind the iris, tube-cornea touch is significantly decreased, therefore decreasing the risk of endothelial decompensation. Ciliary sulcus placement does not require any additional surgery and can be performed by any ophthalmologist who is already skilled in glaucoma surgery by slightly adjusting his or her technique for tube shunt implantation, which decreases the length of surgery, cost and posterior chamber complications and simplifies the logistics of surgical planning when compared with pars plana tube placement.
Eslami and colleagues and Prata and colleagues reported success rates with sulcus implantation similar to those of studies reporting anterior chamber tube placement, with no cases of corneal decompensation. Meanwhile, Weiner and colleagues reported only one case of corneal decompensation in a previously clear native cornea. Sulcus tube placement poses an increased risk for tube obstruction by the iris; however, this complication is easily remedied in the office by a laser iridotomy. Overall, ciliary sulcus tube shunt implantation has been found to be a safe and effective method of controlling IOP.
Over the years, there have been multiple publications describing each of the above three locations for tube shunt placement: anterior chamber, pars plana and ciliary sulcus. To my knowledge, there have been only two retrospective reviews of pars plana vs. anterior chamber tube placement, with no studies published comparing ciliary sulcus vs. anterior chamber placement of tube shunts or ciliary sulcus vs. pars plana. With the growing interest in sulcus placement of tube shunts, further studies directly comparing sulcus vs. anterior chamber or pars plana tube shunt placement are warranted.
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For more information:
Julia Polat, MD, is a Glaucoma Fellow at the UPMC Eye Center and University of Pittsburgh School of Medicine. She can be reached at University of Pittsburgh School of Medicine, Eye & Ear Institute, 203 Lothrop St., 8th floor, Pittsburgh, PA 15213; email: firstname.lastname@example.org
Disclosure: Polat reports no relevant financial disclosures.