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Phaco yields IOP increase in some patients with medically controlled glaucoma
IOP increased in about one-third of eyes with medically controlled glaucoma, and one-fourth of eyes required additional medications or laser trabeculoplasty at 1 year.
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IOP decreased after phacoemulsification in most open-angle glaucoma patients with elevated pressure, but pressure increased in some patients with medically controlled glaucoma and low baseline IOP, according to a study.
“The main point of the paper was that in patients whose intraocular pressure was medically controlled into the statistically normal range, the further lowering effect of phacoemulsification was relatively modest,” study author Mark A. Slabaugh, MD, said in an interview with Ocular Surgery News. “Patients who already had low intraocular pressure prior to cataract surgery sometimes had higher intraocular pressure after cataract surgery.”
Previous studies have not focused exclusively on IOP reduction in patients with medically controlled glaucoma, Slabaugh said.
“Part of the issue is the difference between glaucoma and eye pressure,” he said. “Certainly, eye pressure is the primary risk factor for glaucoma, but there are many patients with glaucoma who have a normal intraocular pressure. In those patients, phacoemulsification is probably not as helpful as in patients who have glaucoma and a high eye pressure.”
The study was published in the American Journal of Ophthalmology.
Study design and methods
The retrospective study included 157 eyes of 157 open-angle glaucoma patients who underwent phacoemulsification.
Diagnosis of glaucoma was based on characteristic optic nerve findings and/or visual field loss.
Patients underwent preoperative gonioscopy showing open angles without peripheral anterior synechiae or areas of appositional closure. Patients with narrow and closed angles were excluded.
Investigators analyzed IOP, use of glaucoma medications, and disease severity and treatment at 1 year postoperatively. They identified patients who showed reduced or stable IOP with no increase in medications or additional laser trabeculoplasty, those who required additional medications or laser treatment, and those with increased postoperative IOP with the same medication regimen.
“I think that what makes this study interesting is that the preoperative characteristics probably more accurately represent what is seen in the average patient who is followed for glaucoma,” Slabaugh said.
Results and relationships
Average IOP decreased significantly, from 16.3 mm Hg preoperatively to 14.5 mm Hg postoperatively (P < .001). Mean number of glaucoma medications increased slightly, from 1.85 preoperatively to 1.92 postoperatively.
IOP increased by 3 mm Hg or more in 10 eyes (6.4%) and deceased by more than 3 mm Hg in 60 eyes (38%).
IOP increased in 60 eyes (38%) with medically controlled IOP at 1 year. Thirty-eight eyes (24%) required additional medications or laser trabeculoplasty. One eye required trabeculectomy.
Average preoperative IOP was less than 20 mm Hg in 20 of 21 eyes that had no change in medication after phacoemulsification but had elevated IOP after surgery.
Preoperative IOP was the single greatest predictor of IOP change after phacoemulsification in open-angle glaucoma patients with medically controlled IOP, the authors said.
Greater age and anterior chamber depth correlated with decreased IOP after phacoemulsification.
Data controlled for age and preoperative IOP showed an association between greater anterior chamber depth and greater IOP reduction.
Anatomic factors
Clinicians do not fully understand why cataract surgery reduces IOP, Slabaugh said.
“As a basic concept, it’s probable that a high intraocular pressure reflects some dysfunction in the outflow system,” he said. “Whatever phacoemulsification does to reverse that dysfunction is not as pronounced when intraocular pressure is already normal.”
Other studies of patients with narrow angles have found a benefit from phacoemulsification, Slabaugh said.
“But in patients who have a wide-open angle preoperatively, there’s probably more than just increasing the angle width further. Other papers have hypothesized that it may be zonular tension passed through the scleral spur into the trabecular meshwork or that the phacoemulsification unit passes ultrasound energy to the trabecular meshwork,” he said. “It’s definitely a real effect, but nobody completely understands the physiologic basis for it.” – by Matt Hasson