This article is more than 5 years old. Information may no longer be current.
Evaluating evidence behind nonpenetrating glaucoma procedures
Experts discuss whether sufficient studies exist to support abandoning trabeculectomy.
Click Here to Manage Email Alerts
Dissatisfaction with conventional approaches to glaucoma surgery has prompted some surgeons to adopt nonpenetrating procedures — deep sclerectomy, viscocanalostomy and their variants. But other surgeons question whether there is evidence to support the perceived promise of the newer techniques.
At the American Academy of Ophthalmology meeting last year, Murray A. Johnstone, MD, explored whether there is a role for nonpenetrating glaucoma procedures.
Dr. Johnstone suggested that surgeons abandon full-thickness glaucoma procedures in favor of trabeculectomy, not because of good clinical trials showing lower IOPs with trabeculectomy, but because in their clinical judgment the full-thickness procedure has an “unacceptable risk-benefit ratio.” He suggested that the same motivation — improvement of the risk-benefit ratio — is at work in the current move toward nonpenetrating procedures.
In an interview, George L. Spaeth, MD, FACS, agreed with Dr. Johnstone that surgeon frustration is a motivating factor for adopting a nonpenetrating approach. But he noted that frustration with trabeculectomy (specifically postoperative complications such as flat or shallow anterior chambers) is as old as the procedure itself.
Ever since glaucoma surgeons discovered more than 150 years ago that they could put a hole in the eye to decrease IOP, Dr. Spaeth said, they have sought to find a method of doing so that would maintain the integrity of the anterior chamber.
“If intraocular pressure could be controlled safely by a surgical procedure, that would be an enormous step ahead,” he said. “I think that’s the philosopher’s stone of glaucoma.”
Finding the stone
The desire to develop a safe and effective glaucoma surgical procedure is so compelling, Dr. Spaeth added, that surgeons who believe they may have discovered such an advance – be it through adjunctive mitomycin, suture lysis or viscocanalostomy – often find it difficult to maintain their objectivity.
“It’s not at all hard to understand why people were unhappy with trabeculectomy,” he said. But, he added, “Trabeculectomy now is not the same as trabeculectomy 2 or 5 or 10 years ago. Why give up something that now works very well for something that requires new learning techniques and which has not yet been demonstrated to be better?”
While the literature on nonpenetrating procedures suggests that they may reduce complications such as hypotony and leaking blebs, that literature is not convincing, Dr. Spaeth said. Furthermore, the classic viscocanalostomy technique does not offer the same efficacy as trabeculectomy for reducing IOP, he said.
“Indeed, it appears that [nonpenetrating procedures] don’t seem to work if they don’t have blebs,” he said.
Most published studies of the newer nonpenetrating techniques, even by the most experienced European surgeons, include follow-up of 2 years or less. (For a discussion of the results of nonpenetrating glaucoma surgery by some of the surgeons most experienced with the techniques, see last year’s two-part round table in Ocular Surgery News Sept. 15, page 78, and Oct. 1, page 12, or click here.)
Newer techniques
“Why isn’t everyone jumping on to this?” Dr. Spaeth asked regarding nonpenetrating procedures.
“Well, a lot of people are,” he said. “But there have been other changes that have occurred at the same time. With releasable sutures, you can almost totally avoid the complications that led people to do deep sclerectomies – that is, specifically, the flat anterior chamber or the shallow anterior chamber and low pressure immediately following the surgery.”
Dr. Spaeth said he thinks the future of glaucoma surgery lies in a modified trabeculectomy, with some type of agent to modify healing (not mitomycin) combined with the use of releasable sutures to control IOP.
In a 2000 survey of American Society of Cataract and Refractive Surgery members regarding glaucoma treatment patterns, 95% of the 725 respondents said they perform five or fewer viscocanalostomies or deep sclerectomies in a given year. The results of the survey, by Dr. Johnstone and colleagues, were published in the Journal of Cataract and Refractive Surgery.
Procedural variations
In his presentation, Dr. Johnstone noted that one of the difficulties in evaluating nonpenetrating approaches is the diversity of intraoperative and postoperative techniques described in the literature.
But John R. Kearney, MD, who has lectured and conducted wetlab demonstrations of viscocanalostomy for hundreds of surgeons worldwide, noted that too much emphasis is put on the procedure’s variations. He added that there is sufficient evidence supporting the efficacy of the procedure – but only the original procedure described by Robert Stegmann, MD.
Dr. Stegmann, the South African surgeon, developed viscocanalostomy to treat a specific population for a specific purpose, and surgeons would be wise to first learn the technique as it was intended before trying to improve it, Dr. Kearney said.
“Most [surgeons] I see who come in are very intimidated by the procedure because it’s very precise,” he said. “Those who stick with exactly what’s being taught will be a success.”
Knowledge
Dr. Kearney shared an anecdote of Charles D. Kelman, MD, who was trying to teach a group of surgeons how to perform phacoemulsification. “One after another, they’re all trying to put their own spin on the thing,” he said. “And Charlie was very insistent that they do it his way.”
The same idea, Dr. Kearney said, applies to viscocanalostomy. In his wetlab demonstrations, surgeons have a tendency to rush ahead, altering the procedure before they are even comfortable with it, he said.
“By the time we’re three steps into the procedure, I can’t recognize what we’re doing,” he said. “We’re a very hard group to teach.”
Dr. Spaeth advised surgeons to assess the clinical evidence before rushing to adopt a new procedure.
“You never make a change until there’s evidence that something is better,” he said. “I’m not saying stick with the old way of doing a trabeculectomy; what I’m saying is do trabeculectomy in a way that is appropriate and new and works.”
For Your Information:
- Murray A. Johnstone, MD, can be reached at 1221 Madison St., Suite 1124, Seattle, WA 98104; 206-682-3447; fax: 206-682-8219; e-mail: murray_johnstone@hotmail.com.
- John R. Kearney, MD, can be reached at 135 County Highway 128, Johnstown, NY 12095; 518-773-2020; fax: 518-762-2022; e-mail: ccc@superior.net.
- George L. Spaeth, MD, FACS, can be reached at the Wills Eye Hospital, 900 Walnut St., Philadelphia, PA 19107; 215-928-3197; fax: 215-928-0166; e-mail: gspaeth@willseye.org.
References:
- Johnstone MA. Is there still a role for nonpenetrating surgery? Presented at: American Academy of Ophthalmology Annual Meeting, Subspecialty Day, Glaucoma; November 14-15, 2003; Anaheim, Calif.
- Johnstone MA, Shingleton BJ, Crandall AS, Brown RH, Robin AL. Glaucoma surgery treatment patterns of ASCRS members – 2000 survey. J Cataract Refract Surg.2001;27:1864-1871.