Augmented trabeculectomy may control IOP in neovascular glaucoma

Satisfactory IOP control in neovascular glaucoma due to proliferative diabetic retinopathy or retinal vein occlusion may be attained through a modified trabeculectomy technique, a study suggested.

“Neovascular glaucoma is a devastating disease that calls for new, creative thinking,” Elie Dahan, MD, first study author, said in an email interview with Ocular Surgery News. He encouraged fellow surgeons to seek innovative surgical approaches.

The modified trabeculectomy technique can be performed alone in pseudophakic and aphakic eyes or in combination with cataract extraction in order to liberate space in the congested eye globe. It involves a trabeculectomy under a large scleral flap, augmented by a penetrating deep sclerectomy, mitomycin C and the use of the T-Flux hydrophilic implant (Carl Zeiss Meditec) as a wick drain that connects the anterior chamber and the enlarged intrascleral space.

“The T-Flux implant was originally conceived and developed to enhance the efficacy and longevity of non-penetrating glaucoma surgery. Since non-penetrating glaucoma surgery cannot work in neovascular glaucoma, I thought of modifying the technique. … I have combined the trabeculectomy and the deep sclerectomy concepts and added to it the T-Flux as a wick drain, rather than a space maker, because it has proved its biocompatibility during many years of use in [non-penetrating glaucoma surgery],” Dr. Dahan said.

Surgical technique

Fourteen eyes of 13 patients with persistently high IOP after panretinal laser photocoagulation underwent this modified procedure. It consisted of a 7 mm × 5 mm × 5 mm trapezoidal scleral flap, a 6 mm × 4 mm × 4 mm deep sclerectomy, application of 0.2% MMC for 3 minutes in the deep scleral bed, a 2 mm × 1 mm trabeculectomy, and the use of the T-Flux to connect the posterior chamber and the deep sclerectomy space via a peripheral iridectomy.

Surgical technique: (A) A fornix-based, 8 × 4 mm conjunctival flap is dissected to expose a large enough area to lift a trapezoidal, 7 × 5 × 5 mm, 50% depth scleral flap. (B) A second 5 × 4 × 4 mm trapezoidal scleral flap is dissected to a depth of 90%, creating a deep sclerectomy without opening Schlemm’s canal. (C) A 2 × 1 mm trabeculectomy is performed at the level of Schlemm’s canal. (D) The iris base is pulled out through the trabeculectomy site. (E) A peripheral iridectomy is performed with Vannas scissors. (F) T-Flux (Carl Zeiss Meditec) hydrogel non-absorbable implant (38% hydrophilic acrylic material), originally conceived to be used as a stent in the deep scleral bed in non-penetrating glaucoma surgery. (G) Artist impression representing augmented trabeculectomy by deep sclerectomy and placement of hydrogel implant (T-Flux) connecting the posterior chamber and the deep sclerectomy site via a peripheral iridectomy. The T-Flux arms are positioned in the posterior chamber behind the iris and the implant leg is secured with a 10-0 nylon suture in the deep sclerectomy bed. Images: Dahan E

If pressure rose above 20 mm Hg during the first 3 postoperative months, as it did in 50% of cases, the filtration site was surgically revised. The conjunctival flap was separated from the sclera, the superficial scleral flap was raised gradually while applying MMC 0.04% in the partially exposed scleral bed until the trabeculectomy opening was reached and aqueous humor flowed freely, the scleral and conjunctival flaps were re-sutured, and the anterior chamber was reformed with balanced salt solution.

According to the study authors, eyes with neovascular glaucoma are known to have a high concentration of transforming growth factors beta 1 and beta 2 in the aqueous humor, which may explain the frequent need for surgical revisions.

“When surgical failure occurs, surgical revision of the filtration site is necessary and also far more efficient than using topical medications,” Dr. Dahan said.

Results

All patients had neovascular glaucoma due to proliferative diabetic retinopathy or retinal vein occlusion. Neovascular glaucoma caused by diabetes is the more aggressive and difficult to control of the two, with surgical failure four times as likely, according to Dr. Dahan. He advised strict management of the diabetes mellitus to enhance the likelihood of success, which in this case was defined as an IOP of less than 22 mm Hg and greater than 5 mm Hg without medications.

All patients underwent postop exams for at least 1 year, with a mean follow-up of 32 ± 12 months. Preoperative mean IOP was 38.7 ± 5.2 mm Hg, decreasing to 17.3 ± 5.2 mm Hg at final follow-up (P = .001). Mean visual acuity also improved from 20/350 to 20/170 (P = .034).

While half of the study eyes required surgical revision, no serious adverse events occurred. Moreover, once IOP control was achieved after 3 months’ follow-up, it remained controlled over the long term. Fifty-seven percent of eyes experienced postop hyphema, but all cases resolved spontaneously without surgical intervention.

In the future, Dr. Dahan hopes to prospectively compare this procedure’s outcomes to those of silicone tubes. – by Michelle Pagnani

Reference:

• Dahan E, Ben Simon GJ. An augmented trabeculectomy for neovascular glaucoma. Ophthalmic Surg Lasers Imaging. 2011; 42(3):196-201.

• Elie Dahan, MD, can be reached at the Ein Tal Eye Center, 17 Brandeis Street, Tel Aviv, Israel 62001; 97235433222; fax: 97235441222; email: elie.dahan@gmail.com.
• Disclosure: Dr. Dahan was previously a member of the scientific board of advisors to IOLTech, the original manufacturer of the T-Flux implant.

Neovascular glaucoma is notoriously difficult to treat, and Drs. Dahan and Simon suggest a surgical technique based on trabeculectomy with mitomycin C plus a hydrophilic wick implant. The study is a clinical case series with all the common limitations of such a design — no control group being chief among them. In addition, since the surgeries were performed between 2000 and 2003, the study did not include a major advancement in the management of ocular neovascularization: the use of angiogenesis inhibitors, such as ranibizumab and bevacizumab. The technique described herein may have a role in the surgical treatment of neovascular glaucoma, but evidence for its use will have to be based on a randomized, controlled, prospective clinical trial incorporating modern management of the disease.

– Joel S. Schuman, MD, FACS
OSN Glaucoma Board Member
Disclosure: Dr. Schuman has no relevant financial disclosures.