Glaucoma incidence, imaging, surgery highlighted at AGS

Issue: May 2004

ByBeth Herskovits

SARASOTA, Fla. — At this year’s American Glaucoma Society meeting, presenters reported on a portable, noninvasive device for imaging Schlemm’s canal, study results of a new trabeculectomy procedure and tips on managing keratoplasty and glaucoma in the same patient.

Keratoplasty and glaucoma

Careful and aggressive management of glaucoma is essential to avoid graft rejection in keratoplasty patients, said Ramesh S. Ayyala, MD, FRCS, FRCOphth.

American Glaucoma Society [logo] The incidence of glaucoma in the early postoperative period after keratoplasty ranges from 9% to 31%; in the late postoperative period, the incidence rises to 18% to 35%, according to Dr. Ayyala. Patients face complications that include hypotony, graft rejection and vision loss, he noted.

“The reason why we miss glaucoma is because we concentrate so much on the cornea,” he said.

To reduce postoperative complications and graft rejections, Dr. Ayyala suggested that glaucoma patients undergo filtering surgery before keratoplasty; bleb revision can then be performed if needed during the corneal transplantation procedure.

In patients who develop glaucoma after keratoplasty, Dr. Ayyala said, surgeons should follow the standard glaucoma protocol, starting with medication, then moving to laser procedures and finally more invasive surgery.

While managing keratoplasty patients, physicians must also take into account their irregular corneal surfaces when performing tonometry, he said.

Topical steroids, while important for controlling ocular inflammation, should be used in limited amounts to avoid corneal epithelial toxicity, he noted.

Glaucoma in American Indians

American Indians have a higher incidence of normal-tension glaucoma than white patients, according to results of the Northwest Trial Vision Project.

While vision loss is known to be the second leading cause of impairment and the sixth leading cause of disability for American Indians, the vision project is the first to calculate the incidence of glaucoma in this population, according to Steven L. Mansberger, MD.

The vision project included 289 participants at least 40 years old who were randomly selected from three tribes. All participants received a full physical examination and an ophthalmic examination that included refraction, perimetry using frequency doubling technology, measurement of limbal anterior chamber depth, confocal scanning laser ophthalmoscopy, nonmydriatic digital imaging and tonometry.

Patients with abnormal results and 30% of patients with normal results then underwent full, dilated exams.

Investigators found that 31% of patients had a complete screening pass with no detectable abnormalities, 23% had diabetes and 11% had a visual acuity of 20/40 or worse.

None of the patients had an IOP greater than 21 mm Hg, and the mean IOP was 12.9 mm Hg. American Indian patients also had a higher cup-to-disc ratio than white patients, Dr. Mansberger said.

Portable imaging of Schlemm’s canal

A portable noninvasive ultrasound device can provide surgeons with valuable information about Schlemm’s canal, according to Richard A. Lewis, MD.

A limited ability to image Schlemm’s canal is one reason there has been “a lack of understanding and progress” in glaucoma surgery, Dr. Lewis said. He described a device developed by iScience Surgical Corp.

The 70-MHz ultrasound machine provides real-time feedback at a higher resolution than ultrasound biomicroscopy, he said.

Dr. Lewis and colleagues successfully scanned Schlemm’s canal in 26 of 27 patients. Scanning failed in one patient who was severely hyperopic, with an unusually small eye, Dr. Lewis said. The average exam lasted 4.6 minutes.

The device has the potential to increase scientists’ understanding of aqueous outflow, as well as to determine why some procedures work in certain patients but not others, he said.

He noted, for instance, that investigators found that Schlemm’s canal seems to shrink after surgery, perhaps because of atrophy from disuse.

“It’s a much more dynamic device than I had envisioned,” he said of the new ultrasound machine. “In the years to come, I hope we’ll have more understanding of the canal.”

Electrosurgical trabeculectomy

Initial results with electrosurgical trabeculectomy are “encouraging,” and the procedure might provide a more affordable approach to glaucoma management, George S. Baerveldt, MD, told meeting attendees.

Dr. Baerveldt presented phase 1 data using the NeoMedix Trabectome, a 19.5-gauge electrosurgical device that is used to remove a strip of trabecular meshwork overlying Schlemm’s canal. The study included 19 Hispanic patients who were taking an average of 1.2 medications preoperatively.

Surgeons achieved success in 89.5% of patients, Dr. Baerveldt said. Only two eyes required a subsequent standard trabeculectomy, either because of IOP that was not controlled with two medications or because of recurrent hyphema.

All patients experienced transient hyphema, which usually resolved in the early postoperative period, according to Dr. Baerveldt. Other complications included localized Descemet’s membrane changes in 18% and transient localized nasal sub-Descemet’s heme in 14%.

Mean postoperative IOP, which was 26.2 mm Hg at entry, dropped to 18.9 mm Hg at 1 day postoperative and to 16 mm Hg at 4 months.

“I believe that the Trabectome studies are very encouraging,” Dr. Baerveldt said. He added that the relatively inexpensive procedure might be ideal for use in patients in developing countries.