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Patient selection key for ab interno trabeculotomy
This surgery is most beneficial if a higher IOP is targeted, study author says.
Ab interno trabeculotomy for treating open-angle glaucoma resulted in most patients failing to achieve a combination of 20% reduction in IOP and a final IOP lower than 18 mm Hg, despite a significant lowering of mean IOP and in the number of postoperative medications, according to a retrospective single-surgeon, single-center case series.
“When we start performing a new procedure in clinical practice, such as with the Trabectome (NeoMedix), we do not always know how well it will work long term,” co-investigator Arthur J. Sit, MD, an associate professor of ophthalmology at the Mayo Clinic, said. “Theoretically, ab interno trabeculotomy should work very well. It targets the trabecular meshwork, which historically has been viewed as the site of abnormal outflow resistance in glaucoma, so removing that meshwork should restore pressure to what it was before glaucoma developed.”
Sit, who has performed approximately 350 ab interno trabeculotomy procedures since 2006, including all the surgeries in the case series, noted that many of these required further intervention, such as a trabeculectomy.
“When you dig a little deeper than many other studies of the procedure and use a strict definition of what constitutes successful surgery, you find that the success rate is actually not very high,” Sit told Ocular Surgery News.
Arthur J. Sit
Defining success
The current study defined success by two main criteria: achieving an IOP of 21 mm Hg or less or at least a 20% reduction in IOP from baseline (criterion A) and achieving an IOP of 18 mm Hg or less and at least a 20% reduction in IOP from baseline (criterion B).
Two more criteria were added to account for biases that might occur with a retrospective study.
“Because we did not start out with a predefined target pressure, we may have been more aggressive in treating some patients and ended up doing surgery earlier than if this had been a prospective study,” Sit said. The two additional criteria were essentially the same as the two main criteria, except patients who had subsequent glaucoma surgery were not considered a failure.
The study, which appeared in the American Journal of Ophthalmology, divided patients into two groups: 88 patients underwent ab interno trabeculotomy only, and 158 patients underwent ab interno trabeculotomy with cataract extraction.
For the two groups combined, mean IOP was reduced 29% at 24 months, from 21.6 mm Hg to 15.3 mm Hg. The number of glaucoma medications was reduced by 38%, from 3.1 to 1.9.
“However, ab interno trabeculotomy with cataract extraction tends to reduce IOP and the number of medications slightly more than ab interno trabeculotomy alone,” Sit said. “This is not surprising because there is a significant amount of data showing that cataract extraction on its own reduces IOP.”
Overall, the success rate was 62% for criterion A but only 22% for criterion B after 2 years.
Minimal complications
Complications were minimal for both groups compared with what is typically encountered with trabeculectomy and glaucoma tube shunts, which lends support to ab interno trabeculotomy in general. Despite postoperative hyphema/microhyphema “being virtually universal” in patients undergoing ab interno trabeculotomy, Sit said that he does not consider it a complication.
“Still, about 5% of patients who undergo this procedure seem to develop recurrent or late hyphemas, even months or years after surgery. This reflux bleeding causes a clouding of the vision but is usually temporary and normally clears without any problems,” Sit said.
However, one study patient experienced an increase in IOP from reflux bleeding that could not be controlled medically and thus required urgent surgery.
“Although ab interno trabeculotomy is actually a very safe procedure, it is important to counsel patients on the surgical risks,” Sit said. “Improving the efficacy, on the other hand, depends on patient selection.”
The patients who fared best in the study were those with exfoliation glaucoma and higher baseline IOP, while patients with primary open-angle glaucoma and past argon laser trabeculoplasty were at higher risk for failure.
“Ab interno trabeculotomy does not usually produce a very low IOP,” Sit said. “The procedure is most appropriate for a target pressure in the high teens to low 20s. Our data show a very high rate of failure for a target pressure of the mid-teens or lower using our stricter study criteria. However, any decision about surgery needs to consider the individual patient situation, and ab interno trabeculotomy may be a reasonable option for patients with lower target pressures if the potential benefit outweighs the minimal added risk.”
As a relatively new device, the optimal surgical technique is still developing. Since starting to perform ab interno trabeculotomy in 2006, Sit no longer fills the eye with viscoelastic because it is not necessary, he said.
“The incision size is small enough that you can bypass these steps and insert the instrument directly,” he said. “This greatly streamlines the procedure and reduces surgical time.” – by Bob Kronemyer