Nonpenetrating Glaucoma Surgery vs. Trabeculectomy – Who is #1?

There has been a growing consensus that we need a better surgery for glaucoma. The tried-and-true trabeculectomy is plagued with early and late scarring leading to failure. Antimetabolites have improved success rates in high-risk cases, but lead to more complications such as hypotony, bleb leaks, and sight-threatening infections¹. Peng Khaw has widely publicized the benefits of a low, diffuse bleb over thin, cystic blebs, achieving similar success rates with less complications². Applying low-dose mitomycin diffusely, facilitated by a fornix-based conjunctival flap, this morphology may be achieved regularly by an experienced surgeon. Yet even the seasoned veteran faces hypotony, bleb failure, blebitis and endophthalmitis.

Nonpenetrating surgery (NPS) has been touted as the next step in the evolution in glaucoma surgery. Just as full-thickness procedures have given way to partial-thickness flaps, some have taken the next step, leaving a thin “Descemeto-trabecular” membrane intact, a so-called “deep sclerectomy”^3,4. The outer portion of Schlemm’s canal can be stripped as well. The surgery is performed under a partial thickness scleral flap, which is loosely sutured. Both a scleral implant3 and mitomycin4 have been effective in maintaining flow with resultant lower IOP after surgery. Some surgeons dilate Schlemm’s canal with viscoelastic at the time of surgery (“viscocanalostomy”)⁵. The latest revision to NPS involves passing a suture 360 degrees around Schlemm’s canal with the help of a lighted probe and tying it in place; the tension on the suture holds the canal open (“canaloplasty”)⁶. The benefit of these additional procedures over deep sclerectomy alone remains to be demonstrated^3-6.

Does nonpenetrating surgery work? There is visible flow at the time of surgery, indicating immediate functionality. The postoperative pressures are in the low to mid teens on average^3-6. The advantages are the lack of sudden decompression of the eye with its attendant complications, limited risk of hypotony, and the lack of need for an iridectomy. The eyes are relatively quiet, comfortable, and easy to manage with a low diffuse bleb postoperatively. The main disadvantage is the increased difficulty and operative time of the procedure, which may discourage the beginning surgeon. Indeed, results vary considerably in the literature, possibly due to surgeon factors.

What should be the first glaucoma operation in a virgin eye? The resultant average pressures are a significant consideration in selecting patients for nonpenetrating procedures. For beginning surgeons especially, these procedures may be most appropriate for the patient with uncontrolled intraocular pressures on maximum tolerated medicines who have little or no apparent optic nerve damage. Nonpenetrating surgery may be preferred in patients who had problems with trabeculectomy in their other eye. As part of a combined procedure, they seem to introduce minimal excess risk to cataract extraction as compared with trabeculectomy⁷. The trabeculectomy has the advantage of lower pressures postoperatively and a longer track record, and thus is generally the procedure of choice for patients with more pronounced glaucomatous damage. That being said, some experienced surgeons may find their results warrant an extended role for nonpenetrating surgery. Other new developments such as the Trabectome and ExPRESS shunt may also have a promising role as a first surgery in many cases.

References:

¹ Rockwood EJ, Parrish RK 2nd, Heuer DK, Skuta GL, Hodapp E, Palmberg PF, Gressel MG, Feuer W. Glaucoma filtering surgery with 5-fluorouracil. Ophthalmology. 1987 Sep;94(9):1071-8.

² Wells AP, Cordeiro MF, Bunce C, Khaw PT. Cystic bleb formation and related complications in limbus- versus fornix-based conjunctival flaps in pediatric and young adult trabeculectomy with mitomycin C. Ophthalmology. 2003 Nov;110(11):2192-7.

³ Shaarawy T, Mermoud A. Deep sclerectomy in one eye vs deep sclerectomy with collagen implant in the contralateral eye of the same patient: long-term follow-up. Eye. 2005 Mar;19(3):298-302.

⁴ Anand N, Atherley C. Deep sclerectomy augmented with mitomycin C. Eye. 2005 Apr;19(4):442-50.

⁵ Stegmann R, Pienaar A, Miller D. Viscocanalostomy for open-angle glaucoma in black African patients. J Cataract Refract Surg. 1999 Mar;25(3):316-22.

⁶ Lewis RA, von Wolff K, Tetz M, Korber N, Kearney JR, Shingleton B, Samuelson TW. Canaloplasty: circumferential viscodilation and tensioning of Schlemm's canal using a flexible microcatheter for the treatment of open-angle glaucoma in adults: interim clinical study analysis. J Cataract Refract Surg. 2007 Jul;33(7):1217-26.

⁷ Cillino S, Di Pace F, Casuccio A, Lodato G. Deep sclerectomy versus punch trabeculectomy: effect of low-dosage mitomycin C. Ophthalmologica. 2005 Sep-Oct;219(5):281-6.

Have a question or comment on this article? Use the “Comment” link above to leave your thoughts, and the author will respond.