The quest to develop new methods for treating the glaucomatous patient in a minimally invasive way whilst reducing the risk
of side effects, has spawned a new generation of surgical approaches and, more specifically, development of the non-penetrating
form of glaucoma surgery.
Richard A. Lewis
Following on from the more than 100-year track record of success of filtering procedures in glaucoma surgery, the current
mainstay of surgical treatment for glaucoma is trabeculectomy, a guarded filtering surgery whereby a sclerostomy is covered
by a 'leaky' scleral flap. During this procedure, a fistula is created in the sclera at the limbus and the aqueous is then
rerouted into a potential space, the subconjunctival area. A successful trabeculectomy procedure is marked by an elevated
conjunctival zone, the bleb, where the aqueous gathers in pockets prior to absorption into the surrounding blood vessels and
lymphatics. In many cases, medication to control scarring, and thus to help prevent closure of the filtration site, is applied
to the eye during the operation or just afterwards.
Although the most popular of surgical techniques in this patient population, trabeculectomy is not without its risks. Complications
can either be immediate; occurring during surgery, or could become evident years after the original procedure was conducted.
These complications include suprachoroidal haemorrhage, choroidal effusion, cataract formation, bleb leaks and bleb infections/endophthalmitis.
Consequently, surgeons have been working to find new surgical methods that would offer both patient and surgeon a better way
of treating glaucoma.
Non-penetrating is best
The idea of using non-penetrating surgery to lower IOP has been around for several years. Today several variations of the
surgery exist, including viscocanalostomy, intended to shunt aqueous back into Schlemms' canal, dilating it without a bleb;
and deep sclerectomy, commonly performed with the use of an adjunctive implant.
This non-penetrating approach does not create a full-thickness hole into the anterior chamber, as with trabeculectomy, the
outflow begins as slow percolation, which prevents rapid decompression of the eye. This is associated with an excellent safety
profile, early postoperative IOP stability and quick recovery time. Surgeons, however, are still apprehensive when it comes
to implementing the technique in their practice.
Earlier non-penetrating techniques have been condemned by specialists for their inability to lower IOP to a level that would
dissuade surgeons from continuing to perform a standard trabeculectomy. Further, many have voiced concerns over the "technically
challenging" nature of the procedure, adding further barriers to universal adoption of the method. Others also claim that
the lack of literature to support this technique is off-putting and so justifies their wait-and-see attitude. However, as
advances have been made in this area of treatment, certain forms of non-penetrating glaucoma surgery have been shown to lower
IOP levels almost to the pressure in normal veins. Surely learning a new technique, as cataract surgeons embraced phacoemulsification,
should not provide a barrier to adoption.
Recently, the inventor of the viscocanalostomy has developed a new procedure that has shown great promise in the surgical
treatment of glaucoma. Robert C. Stegmann, MD, Medical University Pretoria, South Africa has developed a procedure that uses
viscoelastic and a micro-cannula to forcibly open the entire canal of Schlemm thereby reducing IOP levels.
Figure 1: Cannula with lighted tip to identify canal.
The method, canaloplasty, is a non-penetrating surgical procedure to lower IOP in glaucoma utilising the full 360 degrees
of Schlemm's canal and outflow system without creation of a fistula or need for a bleb.
During the 2005 annual ASCRS Symposium, ASOA Congress, Stegmann demonstrated excellent IOP lowering with this procedure when
he recorded an IOP of 12 mm Hg in 92% of his 34 patients, down from an average pressure of 44.5 mm Hg.
How do we do it?