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Canaloplasty shows promise as glaucoma therapy
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LAS VEGAS — Canaloplasty appears to be effective in improving circumferential outflow in patients with primary open-angle glaucoma, according to a surgeon speaking here during the AAO meeting.
Richard A. Lewis, MD, used the iTrack Microcatheter (iScience) to improve outflow through Schlemm’s canal. Canaloplasty is a nonpenetrating, blebless surgical technique in which a suture is passed through Schlemm’s canal with the help of a microcatheter and tied with a small amount of tension to reopen the canal, Dr. Lewis explained.
Dr. Lewis said after Schlemm’s canal is identified and entered with the minicatheter, the surgeon uses a viscoelastic to dilate the entire 360° of the canal. The catheter is then navigated through the canal, which is facilitated by a lighted, flashing beacon mounted on the end of the device.
Once canalization is complete, a suture is threaded through the canal and tied off, Dr. Lewis said.
In a multicenter, prospective study in 92 patients, canaloplasty reduced IOP from a mean of 23.3 mm Hg at baseline to a mean 14 mm Hg at 1 year postop, he said.
“I think this procedure provides an interesting and unique opportunity to work in a space that glaucoma surgeons have not worked in, not only to provide surgical control of glaucoma, but also to provide medical treatment as well, in a long-term example,” Dr. Lewis said.
Follow-up of more patients at 1 year is pending, he said.
The following are additional glaucoma highlights from the AAO meeting. Most of these originally appeared as daily coverage on PCONSuperSite.com.
Sleep apnea may be a risk factor for glaucoma
Sleep apnea may be a significant risk factor for developing glaucoma, according to Parag A. Gokhale, MD.
Dr. Gokhale discussed the results of a meta-analysis evaluating the association between sleep apnea and glaucoma. Sleep apnea is defined as a complete cessation of airflow lasting 10 seconds or more during sleep. Several studies support the association between glaucoma and the sleep disorder, he said.
A Swedish study including 114 subjects suspected of sleep apnea found that 69 patients had sleep apnea, and, of those, five had glaucoma. In a second study, the same researchers examined 30 patients with primary open-angle glaucoma (POAG) and found that six patients also had sleep apnea, Dr. Gokhale said.
Dr. Gokhale also described an American study that reviewed sleep histories of patients with either normal-tension glaucoma or suspected normal-tension glaucoma. They compared the findings to a control group of healthy subjects.
The researchers found that seven of 23 glaucoma patients and three of 14 glaucoma suspect patients had sleep apnea, but none of 30 control patients had the condition.
A Chinese study further supports the association, Dr. Gokhale said. This study found that both abnormal visual fields and suspicious optic discs were more common in patients with severe obstructive sleep apnea than in age-matched controls. Similarly, another study found that 34 patients with sleep apnea had thinner retinal nerve fiber layers than age-matched controls.
On the other hand, two recent larger-scale studies found no association between sleep apnea and glaucoma. But despite this conflicting evidence, Dr. Gokhale said he believes sleep apnea is a risk factor for glaucoma.
“In my glaucoma patients, I do take a brief sleep history and refer these patients for sleep studies if the symptoms are positive,” he said. He urged the audience to do the same.
Dr. Gokhale noted that the most likely etiology to explain the association is ischemic damage to the optic nerve, possibly related to abnormal blood flow autoregulation, hypoxia, hypertension or arteriosclerotic disease.
Focus NTG treatment on targeted IOP reduction
Medications and surgery can each be useful in managing patients with normal tension glaucoma (NTG), but regardless of the approach chosen, treatment should focus on lowering IOP to a targeted level, said Roger A. Hitchings, FRCOphth.
Mr. Hitchings said a number of prospective, randomized studies have underscored the importance of achieving a targeted IOP reduction to prevent glaucomatous progression in NTG. However, recommendations vary, ranging from about 12% to the 30% reduction recommended by the Normal Tension Glaucoma Study, he said.
“If you achieve that target, you can benefit,” he said. Referring to a study performed at Moorfields Eye Hospital in London, he said, “Those eyes with more than a 25% reduction as opposed to those eyes with less than a 25% reduction in pressure ... [had] a statistically significant difference in the time to progression.”
Regarding choice of medication for NTG patients, he said carbonic anhydrase inhibitors can be effective, but they do not work at night. Drugs that act to increase aqueous outflow also are not effective, “because outflow is usually normal in these individuals,” Mr. Hitchings said.
Prostaglandin derivatives have been shown to generate an average 20% IOP reduction when used as initial therapy for NTG, although these drugs reduce IOP by an average of 30% when used in POAG.
“In any event, you want to have a one eye trial, with the other eye as a control” to determine whether an added drug will be of benefit, he said.
Laser therapies are also of little benefit because aqueous outflow is assumed to be normal in NTG patients, Mr. Hitchings noted. Laser trabeculoplasty would be effective only if a NTG patient had an outflow obstruction, he said.
Regarding surgery, randomized, controlled trials comparing trabeculectomy and nonpenetrating procedures have shown that trabeculectomy provides significantly more pressure-lowering effect. More patients treated with trabeculectomy achieve IOPs of 15 mm Hg or lower, he said.