REPRINTED FROM OPHTHALMOLOGY TIMES

THE GLAUCOMA ANGLE

COLUMN #62

New Approaches to Glaucoma Filtering Surgery

Introduction - Robert Ritch, MD

A recent rapid expansion of interest in new alternatives to standard filtration surgery has been receiving increasing attention among both general ophthalmologists and glaucomatologists. Much of the discussion regarding these procedures has been on various groups on the Internet. These new procedures include deep sclerectomy, viscocanalostomy and small incision trabeculectomy avoiding Tenon´s capsule. While a procedure which would have the same result as trabeculectomy with adjunctive antifibrotic agents yet have less postoperative bleb problems would be welcome, none of these procedures has yet been compared to standard trabeculectomy in a prospective, randomized trial. Dr. Fabian Lerner discusses these new procedures and where they stand at the present time. For convenience of the reader in further investigating the literature, an additional list of references is appended at the end of the column. A future column will deal with some other alternatives to standard trabeculectomy in certain instances.

S. Fabian Lerner, M.D.

Departments of Anatomy and Ophthalmology

University of Buenos Aires School of Medicine

Buenos Aires, Argentina

Deep sclerectomy, also known as nonpenetrating trabeculectomy, is an operation that attempts to create a drainage procedure without entering the anterior chamber of the eye. After early descriptions by Zimmerman et al1, ² and Arenas,³ among others, it has been recently popularized in Europe by Philippe Demailly in Paris and André Mermoud in Lausanne.

Deep sclerectomy is indicated in the open-angle glaucomas. The surgical technique involves the creation of a limbus-based conjunctival flap. A 5 x 5 mm scleral flap is dissected, reaching 1 mm into clear cornea at approximately one-third scleral thickness. A triangle or a rectangle of deep sclera is then resected (deep sclerectomy). This sclerectomy is carried out with great care, leaving only a thin layer of sclera over the choroid and the ciliary body posteriorly, and opening the external wall of Schlemm´s canal anteriorly. The corneal stroma is also excised leaving Descemet´s membrane intact. At this point, aqueous humor is seen percolating through the trabeculo-Descemet´s membrane surface. The space left by the deep sclerectomy may be filled with a collagen implant or with high viscosity hyaluronic acid. Closure of the superficial scleral flap is done with 10-0 nylon sutures, and the conjunctival incision is closed with a running 10-0 polyglactin suture. Demailly et al⁴ reported a retrospective study in which they analyzed two groups: one with the use of a collagen implant and the second without the collagen implant. Using the Kaplan-Meier method, the probability of success (IOP << mmHg) without antiglaucoma medication was 68% for the group with the implant, and 69% for the group without the implant, at 18 months follow-up. All patients had POAG without risk factors for bleb failure. In a similar study, comparing the results with and without a collagen implant, Sanchez et al⁵ reported no difference between groups in IOP reduction. However the outcome in the group with the collagen implant was better by Kaplan-Meier analysis at 18 months follow-up. In a poster at the 1998 ARVO Meeting, Hammard et al6 reported their results with deep sclerectomy using intraoperative 5-Fluorouracil in 31 POAG patients, with a follow-up of 9.5 ± 5.2 months. IOP << 20 mmHg was achieved in 48% of the eyes at 6 months without treatment, and this increased up to 95% with medication.

The claimed main advantage of deep sclerectomy is obtaining a filtering procedure without entering the anterior chamber. This is purported to reduce the occurrence of such complications as hypotony, flat anterior chamber and inflammation. The patient usually regains preoperative visual acuity in the early postoperative period. However, success rates appear to be lower than those achieved with conventional trabeculectomy in terms of IOP control. This is a technically demanding procedure that requires excellent surgical skills. Some patients need postoperative goniopuncture with the Nd-YAG laser at the surgical site, when the filtration is suspected to be not sufficient. The advantage of using the collagen implant remains to be proven.

Viscocanalostomywas reported by Stegmann in 1995⁷ As in deep sclerectomy, a superficial scleral flap is followed by the resection of a deep flap, and deroofing of Schlemm´s canal. A thin cannula is used to inject high-viscosity sodium hyaluronate into the canal. The superficial flap is tightly closed, and high-viscosity sodium hyaluronate is then injected underneath the flap to create a reservoir. The conjunctiva is finally sutured. In a poster presented at the 1998 AAO Meeting, Milauskas and Coleman reported their results with viscocanalostomy in 26 eyes with glaucoma (ten with a concurrent phacoemulsification). Preoperative IOP was 22.7 ± 5.9 mmHg, and decreased postoperatively to 19.8 ± 3.8 mmHg. The authors stated that although the IOP reduction was low, the use of glaucoma medication decreased from three preoperatively to zero postoperatively. Carassa et al⁸ had better results in terms of IOP control, although with a short-term follow-up (3.0 ± 2.6 months with a range of 1-10 months). They analyzed the success of viscocanalostomy in 33 eyes. In four eyes, the procedure was converted into a conventional trabeculectomy due to missing Schlemm´s canal or choroidal deroofing. IOP <<21 mmHg was obtained in 25 of the remaining 29 eyes (86.2%) and was <<16 mmHg in 23 eyes (79.3%). Complications included a tear in Descemet´s membrane (7 eyes) and deroofing of the choroid posterior to Schlemm´s canal in 3 cases.

As with deep sclerectomy, viscocanalostomy has the potential advantage of not opening the anterior chamber. This operation does not produce a filtering bleb. Viscocanalostomy is not an easy procedure and requires a learning phase. It should be noted that most of the complications or failures occurred in the first cases done.

Small incision trabeculectomy avoiding Tenon´s capsule is a procedure described by Lerner in 1997.⁹ It is based on a trabeculectomy technique through a corneal incision that was reported by Phillips10 and later modified by Van Buskirk.11 The purpose of this operation is to minimize the surgical trauma to Tenon´s capsule and the episcleral tissue, where the main site for fibrosis and failure is located. A 2.0 - 2.5 mm peritomy is performed at the conjunctival insertion without violating Tenon´s capsule A 2.0 - 2.5 mm linear incision is done at aproximately one-third limbal thickness, in the space between the insertion of the conjunctiva and the insertion of Tenon´s capsule. A spatula blade is used to perform an intrascleral pocket that extends 2 to 3 mm posteriorly. A cystotome, created with a 27-gauge needle and mounted on a syringe with balanced salt solution, is passed through the intrascleral pocket to its end, and is then rotated 90°, cutting the roof of the pocket and entering the subtenon´s space. The anterior chamber is entered at the initial limbal incision, and a fragment of the floor of the pocket is excised using a Kelley Descemet punch or Vannas scissors. After performing a peripheral iridectomy, the wound is water-tight closed in two separate layers with 10-0 nylon: the corneal lip of the incision is sutured to the roof of the pocket, and then the conjunctiva is closed. With a mean follow-up of 7.6 months (range: 6-14), IOP decreased from 34.5 ± 8.1 mmHg to 13.2 ± 4.1 at 6 months, and 90% of the 30 eyes reported had IOP << 18 mmHg without medication. In a poster at the 1998 AAO Meeting, Lerner and Masini evaluated this procedure with adjunctive 5-FU in 25 high-risk glaucoma cases, with a minimum follow-up of 12 months. IOP was << 21 mmHg in 23 out of 25 eyes (91%), six with medication. No serious complications were noted.

Using a small-incision, avoiding Tenon´s capsule dissection and cauterization, getting low-lying blebs and normal depth anterior chambers with good early postoperative visual acuity, are potential advantages of this procedure. Working in a small surgical field and a difficulty in getting enough exposure are disadvantages. This is a penetrating trabeculectomy, as oppose to deep sclerectomy or viscocanalostomy, which are non-penetrating operations.

Is this the end of "conventional trabeculectomy"?. Probably not. Trabeculectomy is the most popular filtering operation with very good success. Ophthalmologists, and particularly glaucoma specialists, have learned to decrease its failure rate and manage its complications. However, innovations are welcome. Performing a glaucoma filtering procedure without opening the anterior chamber, or using a very small incision without damaging Tenon´s capsule is obviously appealing. More cases, longer follow-up and the appropriate prospective randomized clinical trials are needed to evaluate their role in glaucoma surgery.


References

1. Zimmerman TJ, Kooner KS, Ford VJ, et al. Effectiveness of non-penetrating trabeculectomy in aphakic patients with glaucoma. Ophthalmic Surg 1984;15:44-50.

2. Zimmerman TJ, al e. Trabeculectomy vs non-penetrating trabeculectomy: a retrospective study of two procedures in phakic patients with glaucoma. Ophthalmic Surg 1984;15:734.

3. Arenas E. Trabeculectomía ab externo. Highlights of Ophthalmology 1991;19:3-10.

4. Demailly P, Lavat P, Kretz G, Jeanteur-Lunel MN. Non-penetrating deep sclerectomy with or without collagen device in primary open-angle glaucoma: middle-term retrospective study. Int Ophthalmol 1997;20:131-140.

5. Sanchez E, Schnyder CC, Sickenberg M, et al. Deep sclerectomy: results with and without collagen implant. Int Ophthalmol 1997;20:157-162.

6. Hammard P, Plaza L, Quesnot S, Hammard H. Deep sclerectomy and glaucoma disease. First results. Invest Ophthalmol Vis Sci 1998;39:S473. 7. Stegmann RC. Visco-canalostomy: A new surgical technique for open angle glaucoma. An Inst Barraquer (Barc) 1995;25:229-232.

8. Carassa RG, Bettin P, Fiori M, Brancato R. Viscocanalostomy: a pilot study. Eur J Ophthalmol 1998;8:57-61.

9. Lerner SF. Small incision trabeculectomy avoiding Tenon´s capsule. A new procedure for glaucoma surgery. Ophthalmology 1997;104:1237-1241.

10. Phillips CI. Trabeculectomy "Ab externo". Trans Ophthalmol Soc UK 1968;88:681-691.

11. Van Buskirk EM. Trabeculectomy without conjunctival incision. Am J Ophthalmol 1992;113:145-153


Additional References

Chiou AGY, Mermoud A, Hédiguer SEA, Schnyder CC, Faggioni R: Ultrasound biomicroscopy of eyes undergoing deep sclerectomy with collagen implant. BJO 1996;80:541-544.

Chiou AG, Mermoud A, Hediguer SE: Malignant ciliary block glaucoma after deep sclerotomy - ultrasound biomicroscopy imaging. KMA 1996;208:279-281.

Chiou AGY, Mermoud A, Underdahl JP, Schnyder CC: An ultrasound biomicroscopic study of eyes after deep sclerectomy with collagen implant. O* 1998;105:746-750.

Chiou AGY, Mermoud A, Jewelewicz DA: Post-operative inflammation following deep sclerectomy with collagen implant versus standard trabeculectomy. Graefes Arch Clin Exp Ophthalmol 1998;236:593-596.

Fyodorov SN, Koslov VI, et al: Nonpenetrating deep sclerectomy in open-angle glaucoma. Ophthalmic Surg 1990;3:52-55.

Gianoli F, Mermoud A: Combined surgery: Comparison between phacoemulsification associated with deep sclerectomy or with trabeculectomy. Klin Monatsbl Augenheilkd 1997;210:256-260.

Gierek A, Szymanski A: Results of deep sclerectomy for open-angle glaucoma. Folia Ophthalmol Leipzig 1987;12:227-229.

Jacobi PC, Dietlein TS, Krieglstein GK: Microendoscopic trabecular surgery in glaucoma management. Ophthalmology 1999;106:538-544.

Kozlov VI, et al: nonpenetrating deep sclerectomy with collagen. Ophthalmic Surg 1990;3:44-46.

Hara T, Hara T: Deep sclerectomy with trabeculectomy ab externo: one-stage procedure (DS1). Ophthalmic Surg 1989, 20:406-409.

Kampmeier J, Stock K, Hibst R, et al: Intracanalicular trabeculostomy - a new approach in glaucoma surgery. Klin Monatsbl Augenheilkd 1998;212:159-162.

Karlen ME, Sanchez E, Schnyder CC, Sickenberg M, Mermoud A: Deep sclerectomy with collagen implant: Medium term results. Br J Ophthalmol 1999;83:6-11.

Khaw PT, Siriwardena D: "New" surgical treatments for glaucoma (editorial). Br J Ophthalmol 1999;83:1-2.

Mermoud A, Faggioni R, Schnyder CC, et al: Nd-YAG goniopuncture after deep sclerectomy with collagen implant. Invest Ophthalmol Vis Sci 1996;37:1167.

Mermoud A, Karlen ME, Schnyder CC, et al: Nd:YAG goniopuncture after deep sclerectomy with collagen implant. Ophthalmic Surg Lasers 1999;30:120-125.

Mizoguchi T, Matsumura M, Kadowaki H, et al: Visual acuity in patients following trabeculectomy in one eye and trabeculotomy combined with sinusotomy in the fellow eye. Jpn J Clin Ophthalmol 1998;52:185-189.

Ophir A, Mini-trabeculectomy without radial incisions. Am J Ophthalmol 1999;127:212-213.

Vernon SA, Gorman C, Zambarakji HJ: Meidum to long term intraocular pressure control following small flap trabeculectomy (microtrabeculectomy) in relatively low risk eyes. Br J Ophthalmol 1998;82:1383-1386.

Welsh NH, DeLange J, Wasserman P, Ziémba SL: The 'deroofing" of Schlemm's canal in patients with open-angle glaucoma through placement of a collagen drainage device. Ophthalmic Surg Lasers 1998;29:216-226.

Zimmerman TJ, et al: Effectiveness of non-penetrating trabeculectomy in aphakic patients with glaucoma. Ophthalmic Surg 1984, 15:44.

Zimmerman TJ, et al: Trabeculectomy vs non-penetrating trabeculectomy: A retrospective study of two procedures in phakic patients with glaucoma. Ophthalmic Surg 1984, 15:734.

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