Nonpenetrating deep sclerectomy is gaining popularity among physicians

In this variation of the technique, dissection is done using the excimer laser instead of a knife.

ByDaniel Badoza, MD

ByAna C. Sanseau, MD

ByCarlos Argento, MD

Trabeculectomy is currently the preferred surgical technique for glaucoma, but many postoperative complications such as hypothalamia, hyphema and choroidal detachment may occur.

Recently, nonpenetrating deep sclerectomy is gaining popularity among ophthalmologists. The effect on intraocular pressure (IOP) is similar to that of trabeculectomy, but complications are less frequent.

Deep sclerectomy consists of the dissection of a deep scleral flap in order to reach Schlemm’s canal and Descemet’s membrane. A collagen implant, the AquaFlow (STAAR Surgical AG, Nidau, Switzerland), is sutured into the scleral bed to improve aqueous filtration.

Dissecting the deep flap with a blade is technically difficult. Perforation of the anterior chamber is a common complication at the beginning of the learning curve. In this situation, the case must be finished as a standard trabeculectomy.

Laser allows the ablation of the sclera in a homogeneous and controlled way, so the risk of anterior chamber perforation is decreased. The technique was presented as a video in the 1999 Symposium of the American Society of Cataract and Refractive Surgery in Seattle. We performed this technique in seven patients. The longest follow-up time was 7 months and the shortest follow-up time was 1 month.

First, human tissue from eye banks was treated with the excimer laser. By examining these eyes with scanning electron microscopy, the ablation of the external wall of Schlemm’s canal was confirmed. The trabecular meshwork was intact. Patients with early and moderate visual field defects or poor IOP control under more than one medication secondary to open-angle glaucoma were eligible for the technique.

Technique

photograph ---Superficial scleral flap exposing the scleral bed. The yellow square limits the area of ablation of the excimer laser.

The procedure begins by placing a suture through the cornea at the 12-o’clock position. A fornix-based conjunctival flap is created and wet-field cautery is applied.

A superficial flap (4 to 5 mm) is dissected with a diamond blade calibrated to a depth of 400 µm, advancing 2 mm into the clear cornea (Figure 1).

The sclera is ablated with the excimer laser (117 Technolas; Bausch & Lomb Surgical, Claremont, U.S.A.) at a fluence of 160 mJ. Bausch & Lomb Surgical designed a specific program that determines the width and depth of the ablation. The first sequence of pulses ablates 100 µm. Seven additional sequences ablate 20 µm each.

The eye is rotated downward to ensure correct vertical entry of the laser beam. The laser creates a square figure in a controlled way, which reduces the risk of anterior chamber perforation.

Between sequences of excimer ablation, the surgeon may check for any aqueous humor filtration through the opened Schlemm’s canal. When the aqueous humor begins to percolate through the trabeculo-Descemet’s membrane, the ablation is stopped. Air is used to keep the area dry during the entire ablation process.

As only the external wall of Schlemm’s canal is opened, most of the trabecular meshwork is intact, preventing anterior chamber shallowing. In this case series, we did not strip the inner wall of Schlemm’s canal. If necessary, the stripping may be performed either manually or by adding more laser pulses.

The AquaFlow collagen device is placed radially and sutured with one 10.0 nylon bite. The scleral flap is repositioned and sutured over the collagen implant. The conjunctiva and Tenon’s capsule are closed.

During follow-up, the surgical area is examined by UBM. Gonioscopy is required for early detection of possible goniosynechiae, especially in the first month.

In six patients, as IOP failed to regulate below 16 mm Hg, we opened the trabeculo-Descemet’s membrane with YAG laser, turning this nonpenetrating surgery into an open one without the postoperative complications of conventional trabeculectomy.

Advantages of procedure

photograph ---Collagen implant is sutured to the scleral bed.

The major advantage of this procedure is that it prevents sudden postoperative hypotony by inducing a progressive filtration of aqueous humor through a homogeneous trabeculo-Descemet’s membrane under direct vision.

Unroofing Schlemm’s canal with the excimer laser is a new nonperforating procedure enabling ablations of scleral tissue to be safer. The absence of postop complications as reported with trabeculectomy is remarkable. In the sixth case, there was a small perforation of the trabeculo-Descemet’s membrane. We performed an iridectomy. The collagen implant was sutured to the scleral bed. On the first postop day, the anterior chamber was well formed and IOP was 10 mm Hg. The need to open the trabeculo-Descemet’s membrane in almost all of the cases showed a tendency of hypofiltration.

This method allows an effective IOP decrease involving minimal risk and little disruption of the patient’s daily life. Randomized studies with longer follow-up, comparing this technique with viscocanalostomy and trabeculectomy, will determine its role in the management of glaucoma.

For Your Information:

Carlos Argento, MD, can be reached at Instituto de la Visión, University of Buenos Aires, Marcelo T. de Alvear 2261, 1122 Buenos Aires, Argentina; +(54) 114-827-7900; fax: +(54) 114-823-5721; e-mail: dabadoza@fibertel.com.ar. Dr. Argento has no direct financial interest in any of the products mentioned in this article, nor is he a paid consultant for any companies mentioned.

Bausch & Lomb Surgical can be reached at 555 W. Arrow Highway, Claremont, CA 91711 U.S.A.; +(44) 1-344-30-03-30; fax: +(1) 909-399-1525. STAAR Surgical AG; Hauptstrasse 104, CH 2560 Nidau, Switzerland; +(41) 32-332-8888; fax: +(41) 32-332-8899.