Researchers work to expand options for glaucoma surgery

Issue: April 2001

Glaucoma treatment is garnering an increasing amount of attention in the ophthalmic community, not just on the pharmaceutical side but also on the surgical side. Surgeons and researchers around the world are continually perfecting existing techniques and conceiving new procedures such as non-penetrating deep sclerectomy, deep sclerectomy with compressed air and electric burr, non-perforating schlemmectomy, excimer laser trabeculostomy and pneumatic trabeculoplasty.

Non-penetrating deep sclerectomy

Researchers are calling non-penetrating filtration surgery for glaucoma one of the most progressive directions in which glaucoma treatment is heading. Tatiana V. Kozlova, MD, reported in Ocular Surgery News, that sinusotomy, the first non-penetrating procedure, was described in 1964 by a Russian ophthalmologist. In this country, Thomas Zimmerman, MD, further developed the technique, now called non-penetrating deep sclerectomy (NPDS).

In 1985 and 1986, another Russian, Valentin Kozlov, MD, substantiated using the peripheral part of Descemet’s membrane for outflow in the projection of Schwalbe’s ring. In clinical intraoperative studies of hemodynamics, he proved that after opening Descemet’s membrane, IOP was substantially reduced. Also according to Dr. Kozlova’s description, the coefficient of the facility of outflow increased, when compared to the values after the first stage of the operation, which is opening Schlemm’s canal.

According to Dr. Kozlova, this premise is the basis for the second generation of NPDS. Simultaneously, glaucoma implants to control postoperative healing were being developed.

NPDS, Dr. Kozlova describes, is complicated. It begins as a classical trabeculectomy and has a perforation rate of 5% to 11%, even in the most experienced hands. Dr. Kozlova described the procedure in her and her colleagues’ training experience.

First, a short, curved probe with a groove is used to open Schlemm’s canal. A fine microspatula is used to gently separate the corneal-scleral tissue over the surface of Descemet’s membrane. Dr. Kozlova and colleagues use a cutting board instrument, placing it between the trabeculo-descemetic plane, then separate the overlying corneal-scleral tissue.

Residual layers of sclera and cornea are removed over the cutting board spatula with a blade or are ablated with excimer-laser irradiation. The surgeon then removes the spatula and cleans the surface of Descemet’s membrane with a polisher to obtain sufficient filtration. Fluorescein staining is used for better visualization and preventing of penetrations.

Compressed air, electric burr

A new approach to deep sclerectomy uses compressed air and an electric burr to dig into the sclera, down to Schlemm’s canal. This approach, described at the Italian Ophthalmologic Society, was developed in 1999.

According to Fabio Ferentini, MD, of the Legnano Hospital, and colleagues, the technique makes deep sclerotomy easier and faster. Air dehydrates the tissue under the sclerocorneal flap, making it rigid and more compact. Ferentini said the burr can then easily work down to the desired depth.

The procedure begins by detaching the conjunctiva from the limbus between the two upper quadrants. A hemostatic sponge is applied between the sclera and conjunctiva for 1 or 2 minutes. Dr. Ferentini then makes a 250-µm deep, 5-mm by 5-mm by 5-mm incision with a corneal hinge and extends it 1 mm into the clear cornea. He then dissects the flap with a ruby knife.

Next, purified, filtered, compressed air is applied into the flap, dehydrating the surface for about 30 seconds. Burrs of 3 mm are used, and rotation speeds of 600 rpm to 1,500 rpm are recommended. Dr. Ferentini explained that while the burr is working, compressed air is constantly applied to the tissue.

When the trabecular meshwork is exposed, then filtration begins. The anterior portion of the scleral bed is deepened with the burr up to the corneal hinge, Dr. Ferentini explained, once the aqueous outflow has begun. This creates a large anterior decompression chamber, and the flap is then sealed with 9-0 nylon sutures.

This technique takes quite a long time to learn, as with other deep sclerotomy methods. Dr. Ferentini reported that 20 operations are necessary to gain confidence.

Non-perforating schlemmectomy

A study presented at the American Society of Cataract and Refractive Surgery’s Symposium on Cataract, IOL and Refractive Surgery shows that excimer ab externo excision of Schlemm’s canal may be an effective treatment for glaucoma.

The idea of “schlemmectomy,” according to Oswaldo Borras, MD, comes from the external excimer trabeculectomy procedure of Arturo Maldonado Bas, MD, and the viscocanalostomy technique developed by Robert Stegmann, MD.

In the study, photoablation was performed using the Nidek EC-5000 excimer laser, stopping ablation immediately after obtaining aqueous humor. A spatula was applied on the ablation zone to verify that the procedure was non-perforating. Dr. Borras said that the scleral flap in the 22 treated patients was closed with 10-0 nylon and 8-0 virgin silk.

One day after schlemmectomy, patients had good filtering blebs. Dr. Borras said immediately postoperatively there is a quiet eye without hyphema, flare or ciliary response. He added that the most important advantage of this technique is preventing sudden postoperative hypotony.

Excimer laser trabeculostomy

Researchers at the Ninth Annual Ocular Surgery News Symposium described the surgical treatment for glaucoma of excimer laser trabeculostomy (ELT). The technique relies on the eye’s existing intraocular drainage channels to treat anatomic pathology inherent in open-angle glaucoma.

ELT corrects outflow obstruction at the juxtacanalicular trabecular meshwork and the inner wall of Schlemm’s canal. Michael S. Berlin, MD, explained that ELT consists of placing the laser delivery probe in contact with the trabecular meshwork through a paracentesis and creating multiple perforation sites directly into Schlemm’s canal. The procedure uses a photoablative, rather than photothermal, laser.

Initial trials of ELT involved 30 eyes in Switzerland and Germany. Patients in this study were followed for up to 9 months; the mean IOP reduction at 6 months was 7.2 mm Hg. Dr. Berlin said that fiber diameter, and therefore hole size, did not seem to have a significant effect on the long-term efficacy of the procedure.

He said that parameters of ELT are being refined to optimize the procedure’s efficacy. Parameters depend on both the laser and the tissue. Dr. Berlin explained that the laser factors include beam output homogeneity, minimal pulse-to-pulse energy variation, delivery system focus for supra-threshold fluence and the ability to control the thermal component of the laser-tissue interaction as it occurs.

Tissue factors, according to Dr. Berlin, include target anatomy, controlling shape and thickness of the trabecular meshwork, determining landmarks in depth and preventing an inflammatory response from inciting healing at the surgical site.

Dr. Berlin believes that, in the near future, ELT will succeed in fistulizing the anterior chamber to an internal, rather than an external, outflow channel.

Pneumatic trabeculoplasty

Pneumatic trabeculoplasty is the brainchild of Leo Bores, MD. So far, there is very little data supporting the technique; it is not approved by the Food and Drug Administration.

Dr. Bores’ theory is based on the fact that post-LASIK patients have lower IOP. He thought that perhaps the suction ring that stretches the trabeculum during LASIK actually results in an increased outflow of aqueous from the trabecular meshwork. Eric Knight, OD, told Primary Care Optometry News that Dr. Bores began putting the suction ring on non-LASIK patients, and it lowered their IOP, according to Dr. Bores.

“The procedure needs to be done, according to Dr. Bores, two to four times,” Dr. Knight said. “He explains that it is like a rubber band being stretched … if you do it a few times, eventually [the trabeculum] stays open. His theory makes sense in some respects, but there are some serious concerns about the procedure, and more studies need to be done.”

For Your Information:

Tatiana V. Kozlova, MD, is from the department of glaucoma and high myopia surgery at the Intersectoral Research — Technical Complex Eye Microsurgery. She can be reached at fax: (95) 485-5954; e-mail: t.kozlova@mtu-net.ru. Dr. Kozlova has no direct financial interest in the products mentioned in this article, nor is she a paid consultant for any companies mentioned.

Fabio Ferentini, MD, is head of the Legnano Eye Clinic. He can be reached at Ospedale C. Cantu, Piazza Mussi 1, Abbiategrasso (MI), Italy; (39) 02-9486202; fax: (39) 02-9486350. Dr. Ferentini has no direct financial interest in any of the products mentioned in this article, nor is he a paid consultant for any companies mentioned.

Oswaldo Borras, MD, can be reached at Sarmiento 2640, Montevideo 2640 Uruguay; (598) 2-7114222; fax: (598) 2-7093931; e-mail: borras@netgate.com.uy. Dr. Borras has no direct financial interest in the products mentioned in this article, nor is he a paid consultant for any companies mentioned.

Michael S. Berlin, MD, is director of the Glaucoma Institute/Beverly Hills. He can be reached at 8733 Beverly Blvd., Los Angeles, CA 90048-1800; (310) 855-1112; fax: (310) 855-1211; e-mail: berlin@csmc.edu. Dr. Berlin has no direct financial interest in any of the products mentioned in this article, nor is he a paid consultant for any companies mentioned.

Eric Knight, OD, can be reached at Knight Vision and Glaucoma Specialists Inc., 7300 West Greenfield Ave., West Allis, WI 53214; (414) 453-6667; fax: (414) 774-5505; e-mail: ericknight@aol.com. Dr. Knight has no direct financial interest in any of the products mentioned in this article, nor is he a paid consultant for any companies mentioned.