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CHICAGO -- For the first time in a multicenter randomized trial, minimally invasive glaucoma surgery (MIGS) with an intracanalicular (Schlemm's canal) stent significantly reduced long-term vision loss as compared with MIGS alone.

Over a 5-year period, the annual rate of progression in vision loss averaged 0.49 dB with surgery alone, compared with 0.26 dB with surgery plus a Schlemm's canal microstent (Hydrus). The results translated into a 47% difference in the rate of progression in favor of the patients who received stents.

The decline in intraocular pressure (IOP) from baseline averaged 8-9 mmHg from 12 to 60 months in both treatment groups. More patients who received stents required no IOP medication at 5 years, reported Gus Gazzard, MD, of Moorfields Eye Hospital and University College London, at the American Academy of Ophthalmology (AAO) meeting.

"This is the first demonstration of a mixed procedure affecting, or protecting, visual fields," said Gazzard. "It's a 5-year continuous follow-up, multicenter randomized controlled trial with very robust outcomes and a robustly conducted study. There was a reduced rate of visual field loss with the Hydrus stent compared to cataract surgery alone, which I think is really quite powerful.

"The greatest effect was observed, as one might expect, amongst those that were fast progressers, and that effect can be explained by the in-clinic intraocular pressure alone," he continued. "We don't know what happens out there, as is normally the case with our patients."

The results added to previous reports from the randomized trial. The study met the , showing that significantly more patients randomized to surgery plus stents had a reduction in unmedicated IOP ≥20% from baseline to 2 years. Additionally, patients in the stent group had a greater reduction in IOP medication use. Earlier this year, Gazzard and colleagues reported that the 24-month benefits were and that fewer reoperations occurred in the stent group.

The AAO presentation focused on data related to disease progression (measured in decibels) and whether the addition of the stent slowed progression compared with surgery alone. With the aid of , investigators tracked changes in sensitivity within individual patients' visual field. The methods allowed the researchers to examine changes in specific points in the visual field, clusters of points, and overall rates of progression for the two patient groups, said Gazzard.

The HORIZON trial involved 556 patients with mild or moderate primary open angle glaucoma. They were randomized 2:1 to MIGS plus the stent or MIGS alone. The study population had a median age of 71, baseline mean best corrected visual acuity of 20/40, median unmedicated IOP of about 25 mmHg, median medicated IOP of about 18 mmHg, and a mean of 1.7 IOP medications.

The post-hoc analysis of change in visual field included 352 patients from the stent group and 165 from the surgery group. The 0.23 dB difference in annual visual-field loss between the groups achieved statistical significance (P=0.0138).

During a discussion that followed the presentation, Robert Stamper, MD, of the University of California San Francisco, speculated about the reason for the decreased rate of visual field deterioration when the two groups had similar mean IOP.

"The thing that jumped to my mind was the possibility of a more even intraocular pressure [in the stent group] over the 24-hour period, which is sort of what we have seen for both laser and for trabeculectomy, at least in terms of perhaps their protective value," said Stamper.

Limited data have been published on 24-hour IOP control with the stent, said Gazzard, who suggested two possible explanations for the visual field benefit.

"I think the two possibilities are noncompliance and the other is the flattening of the diurnal curve," he said. "I suspect it's going to be a combination of both in this study. Clearly, there was a difference in the medication rates in this study, and so compliance in the cataract surgery patients, who were more heavily medicated, could be more of a confounding factor. Whether or not that is sufficient to explain theses results, I doubt."

"I suspect it's showing us that probably there is some degree of flattening of the diurnal curve," Gazzard added. "Let's remember that there was a significant proportion of cataract surgery-only eyes that remained medication free, so I think that compliance or noncompliance rates as a cause of this is probably less contributory than the actual physiological flattening of that diurnal curve with the addition of a stent."

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