Filtering surgery

Optometric Management, Aug 2001 by Gelvin, John

Technological developments you should know about.

Most of you are probably familiar with modern trends of trabeculectomies. Antimetabolites such as 5-fluorouracil and mitomycin C have successfully lowered intraocular pressure (IOP) into the low teens without the use of medications postsurgery. Releaseable or laserable sutures of the scleral flap allow IOP to be slowly reduced over a 4-week post-op period, reducing hypotony. However, you might not be aware of these newer developments in filtering surgery.

* Deep sclerectomy. Unlike trabeculectomy, deep sclerectomy is a nonpenetrating surgical procedure. The trabecular meshwork remains intact and the anterior chamber isn't penetrated. Uveoscleral outflow through the subconjunctival space is increased. There are two types of deep sclerectomy:

* Viscocanalostomy. Developed about 2 years ago but undergoing study at present, this form of deep sclerectomy restores the original uveoscleral outflow pathway in the eye by removing a segment of Schlemm's canal and injecting a thick viscoelastic into the canal to prevent fibroblast formation. This procedure is difficult and is used for patients with extraordinarily high IOP. It doesn't achieve IOPs as low as trabeculectomy; goals are the upper teens instead of mid-teens. However, it prevents the large filtration blebs trabeculectomy causes.

* Wick implants. This procedure is currently moving through the FDA approval process. A small collagen wick is inserted into the subconjunctival space and placed behind the trabecular meshwork after the sclera is removed. It's designed to maintain the intrascleral space. Initial reports confirm a pressure-lowering effect similar to that of viscocanalostomy.

Trabeculectomy still gives the best IOP-lowering results, but keep up with the research because it's changing all the time.

A Vaccine for the Optic Nerve?

Multiple sclerosis drug shows promise.

Professor Michal Schwartz of the Weizmann Institute in Rehovot, Israel, has demonstrated that vaccination with glatiramer acetate (Copaxone), a drug that treats multiple sclerosis, may protect the optic nerve.

Dr. Schwartz and her associates discovered that cell death resulting from increased intraocular pressure (IOP) initiates the release of chemicals such as glutamate at toxic levels that may damage neighboring healthy cells in a process called "secondary degeneration." To combat this, Dr. Schwartz tried to enlist the body's immune system using fragments of proteins from the outside covering of the nerve. Vaccinations with these proteins prevented optic nerve degeneration, but she next needed to be sure of which specific protein fragments wouldn't cause autoimmune disease.

She discovered that glatiramer acetate was a safe synthetic alternative to use in rats. Rats with high IOP showed only a 4% loss of cells when vaccinated with glatiramer acetate as opposed to a 28% loss in rats that weren't vaccinated.

Because Copaxone is already FDA-approved, scientists hope that human trials can begin soon.

BY JOHN GELVIN, O.D., F.A.A.O., Kansas City, Mo.

Dr. Gelvin is with Glaucoma Services at Hunkeler Eye Center in Kansas City, Mo.