Microstent Reduces Post-Cataract Surgery Intraocular Pressure in Glaucoma Patients

By Will Boggs MD

February 11, 2020

NEW YORK (Reuters Health) - Microstent implantation in Schlemm's canal reduces early postoperative intraocular pressure (IOP) following cataract surgery in patients with mild or moderate glaucoma, according to findings from the HORIZON study of the Hydrus microstent.

"This study suggests that the use of Hydrus microstent may protect against very high post-operative IOPs (that can result in morbidity in already vulnerable glaucomatous eyes)," Dr. Nazlee Zebardast of Massachusetts Eye and Ear Infirmary, Harvard Medical School, in Boston, told Reuters Health by email. "However, whether this justifies a permanent implant is unclear."

Acute post-cataract surgery IOP elevation occurs more frequently in glaucoma patients and can result in optic-nerve damage. Oral carbonic-anhydrase inhibitors can reduce this risk in some patients, but they cannot be used safely in all patients.

The Hydrus microstent is designed to increase outflow through the trabecular outflow pathway and was shown in the HORIZON study to provide a higher incidence of IOP reduction, larger mean IOP reduction, and greater reduction in medication at 24 months, compared to eyes with cataract surgery without stenting.

In the current study, Dr. Zebardast and colleagues compared early postoperative IOP changes in patients who underwent cataract surgery alone (187 eyes) with those in patients who underwent cataract surgery combined with implantation of a Hydrus microstent (369 eyes) in the HORIZON study.

On postoperative day 1, IOP in the microstent group had decreased by a mean 8.5 mm Hg, compared to an increase of 2.2 mm Hg in the group without stenting (P<0.001), the team reports report in Ophthalmology.

The incidence of IOP spike of >40 mm Hg on postoperative day 1 was significantly lower in the stented group (1.4%) than in the nonstented group (14.4%).

Similarly, the incidence of IOP spike of 10 mmHg or more was lower in the microstent group (3.0% vs. 22.5% in the nonstented group), as was the incidence of IOP requiring medication (8.1% vs. 41.2%, respectively).

At postoperative week 1 and postoperative month 1, there were similar differences between the groups, but the magnitudes of these differences were lower than at postoperative day 1.

In multivariable analysis, older age and prior selective laser trabeculoplasty were independently associated with significantly higher odds of postoperative IOP spike, whereas presence of the Hydrus microstent was independently associated with significantly lower odds of postoperative IOP spike.

"These findings are very interesting and may indicate certain groups may require more careful monitoring but require further confirmation," Dr. Zebardast said.

"Clinicians should be aware that our study conditions do not necessarily simulate real clinical practice," she cautioned. "The HORIZON study selected for eyes with high baseline IOP which may be more likely to benefit from the device. Additionally, eyes are not normally washed out of IOP lowering medication prior to surgery as was the case in this study."

"We are also limited by the data collected as part of the study and therefore cannot assess other unmeasured confounding factors nor compare the effectiveness of the microstent against prophylactic post-op IOP-lowering medication use," Dr. Zebardast said.

"Future studies are needed to examine additional individual risk factors for IOP rise, and compare these benefits against the ability of medications such as acetazolamide to prevent similar IOP rises," the authors note.

Ivantis Inc., which makes the Hydrus microstent, provided funding for the HORIZON study but had no role in the design or conduct of the current study. None of the authors reports conflicts of interest.

SOURCE: https://bit.ly/2vcchuI Ophthalmology, online January 22, 2020.

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