spotlight on technology &
Canaloplasty:A Promising New Extensionto Non-Penetrating Surgery
Leslie Goldberg, Assistant Editor
PHOTOS COURTESY OF DR. ROBERT
a recent advancement in non-penetrating glaucoma surgery, is designed to improve
the aqueous circulation through the trabecular outflow process, according to John
R. Kearney, M.D., founder and director of The Cataract Care Center, N.Y. The canaloplasty
procedure attempts to enhance aqueous outflow without creating a bleb. Pilot studies
and early multisite studies have achieved promising results, says Dr. Kearney.
Kearney, an early investigator of the viscocanalostomy procedure that he learned
from its originator, Robert Stegmann, M.D., of Pretoria, South Africa, was also
one of the first surgeons to dilate 360° of Schlemm's canal using a flexible
microcannula. In this dilation study, a significant reduction in postoperative IOP
was obtained by circumferential dilation. During this study, Dr. Kearney introduced
the dilation procedure to Dr. Stegmann, who in turn added the placement of an intracanalicular
tension suture, creating the canaloplasty procedure.
Introduction of the microcatheter into Schlemm's canal.
What is a Canaloplasty?
A canaloplasty is a 360° viscodilation of the Schlemm's canal
with an illuminated beacon-tipped microcatheter. The microcatheter is used to place
an intracanalicular suture that cinches and stretches the trabecular meshwork inwards
while permanently opening Schlemm's canal, explains Dr. Kearney. The difference
between a viscocanalostomy and a canaloplasty is that the canaloplasty aims at opening
the entire length of the canal, not just one section of it. The procedure restores
the natural drainage of fluid from the eye, thus reducing IOP.
"Nearly 90% of patients do not require glaucoma drops after the
surgery," says Dr. Kearney. "It has been evaluated on primary open-angle glaucoma,
pseudoexfoliative glaucoma and pigmentary glaucoma. Theoretically, it should work
on most types of glaucoma, as does viscocanalostomy, even after drops, pills, laser
and other types of glaucoma surgery have failed." Complications are far less frequent
and less severe than in most other types of glaucoma surgery, says Dr. Kearney.
The canaloplasty begins similar to a viscocanalostomy. As in viscocanalostomy,
parabolic superficial and deep scleral flaps are produced. (The superficial flap
should be between 200-250 microns thick). The deep flap is dissected to the plane
of Schlemm's canal and the sides of the deep flap are then dissected forward into
the cornea. Reflection of the inner flap unroofs Schlemm's canal, creating a trough
leading to two entrances into Schlemm's canal (surgical ostia). Further reflection
of the flap creates an intact window in Descemet's membrane, and gentle pressure
at the level of Schwalbe's line, using a cellulose sponge, extends the window. Aqueous
humor diffuses through this window into a subscleral space (lake).
microcannula is introduced into the entrance of Schlemm's canal, and advanced 360°
while high-viscosity sodium hyaluronate is gently injected into the canal to force
open the entire length
(Figure 1). A 10-0 suture is tied to the microcannula
and withdrawn through the canal. The suture is tied together as a pursestring to
apply tension on the trabecular meshwork and open the canal (Figure 2). A double-suture
technique, adopted by Drs. Stegmann and Kearney in 2005, further reduces the likelihood
of closure through scar formation and pressure rise, especially if one suture loosens.
The deeper scleral flap is excised (deep sclerectomy) and the
superficial flap is sutured securely. Tight closure is mandatory to prevent bleb
formation. High-viscosity sodium hyaluronate is then injected into the subscleral
lake to act as a physical barrier to fibrinogen migration postoperatively.
"Making a parabolic superficial flap leaves no sharp corners as
in a rectangle, square or triangle flap," says Dr. Kearney. "These corners tend
to leak, which is essential in trabeculectomies. A curved edge is easier to close
tightly and prevent leakage. This is desirable in viscocanalostomy and canaloplasty,
as you want the flow of aqueous to channel into Schlemm's canal and exit the eye
via the collector channels, i.e., internal filtration as opposed to external filtration."
Figure 2. A 10-0 polypropylene suture being
tied around the end of the microcatheter.
iScience Surgical's Microcannula
The iScience Surgical (Menlo Park, Calif.) Ophthalmic Microcannula
(OM) has become an important piece of equipment used in performing this procedure.
iScience Surgical's OM is used to insufflate Schlemm's canal with viscoelastic as
part of the canaloplasty technique and serves as a means for placing the drawstring
suture to open Schlemm's canal, said Dr. Stegmann in an interview with Eurotimes.
The microcannula has a diameter of 200 microns and an atraumatic
tip. An LED light source shone through an optical fiber illuminates the catheter
tip, which also contains a lumen for the injection of high-viscosity sodium hyaluronate.
The surgeon can see the pulsed red flash at the catheter's tip and knows where the
catheter is at all times.
Additionally, a new high-resolution ultrasound system, also produced
by iScience Surgical, provides accurate localization of Schlemm's canal and can
also provide confirmation of the success of the procedure.
"iScience Surgical's microcannula allows surgeons to dilate Schlemm's
canal 360°. Previously, surgeons were only able to dilate 120° of the
canal. This added dilation allows the surgeon to potentially allow flow of aqueous
to pass through the entire trabecular meshwork, where the greatest resistance to
outflow is believed to be located." notes Dr. Kearney.
Criteria for Success
"I believe that the procedure is a success if the IOP is lowered
sufficiently to prevent further optic nerve damage without the use of pressure-lowering
medications," says Dr. Kearney. "I don't believe in just a percentage drop in IOP,
but rather to a target range. We are now seeing pressure drops to the low-to-mid
teens, lower in some cases, but the actual statistical results are being compiled
for an evidence-based, peer-reviewed article."
Ophthamology Management, Issue: March 2006