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Changing demographics lead to more primary angle closure glaucoma in US
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SAN ANTONIO – Primary angle closure glaucoma is a bigger problem than many believe, according to Robert M. Feldman, MD, from the UT Health Science Center, who gave the President Lecture at the Optometric Glaucoma Society meeting here prior to the American Academy of Optometry annual meeting.
The percentage of people who go blind from this type is much higher than with open angle glaucoma, he said.
Changing demographics affect its prevalence rates, especially in the U.S., where the Asian population has grown immensely. The condition often affects the aging population with an increased lens thickness, he said.
A patient with 180 degrees of nonvisible posterior trabecular meshwork by gonioscopy in primary gaze would be a primary angle closure (PAC) glaucoma suspect, he said.
“PAC means that you at least have elevated pressure or a peripheral anterior synechiae (PAS), which would typically be superior, or you would require some IOP-lowering medication. The pigment on the surface of the trabecular meshwork looks smudged, giving you some evidence that angle closure has occurred,” Feldman added. “Primary angle closure glaucoma is PAC with evidence of glaucoma, whether it’s optic nerve, visual field, nerve fiber loss – anything that would tell us there’s actual damage occurring.”
He focused his talk on the chronic, subacute and asymptomatic chronic angle closure glaucoma subtypes.
Chronic primary angle closure is the most common form, Feldman said.
“It is appositional angle closure with or without permanent PAS and results in elevated IOP,” he said. “Usually patients are asymptomatic, and it can develop in eyes with previously open angles.”
Not all eyes with equally narrow angles develop angle closure. Choroidal thickness, lens size, angle width and iris thickness all have an impact on this.
There is always a normal contact between the iris and the lens, he said. There is always a higher pressure behind the eyes than in front.
“You see differences in changes in iris volume from POAG to PAC; you also get choroidal volume changes that occur dynamically,” he added.
Previous research showed that eyes with PAC had greater macular choroidal thickness than normal eyes, he said. Today, practitioners are doing 360-degree video reconstruction of anterior segment OCT.
With trabecular-iris circumference volume, researchers are measuring iris volume and looking for predictive parameters for angle closure, he said.
Feldman and his team have identified a new landmark called BELL: band of extracanalicular lamina.
“We thought this was a trabecular meshwork shadow and it had been reported previously in literature as such,” he said.
“It becomes a very useful landmark in the anterior segment. There’s a point at the limbus where you get a change in scleral fibers. There is a change in structure there, a real structure, not an artifact on anterior segment OCT,” Feldman said. “If you follow the anterior layer around, it will always take you right to the scleral spur. It gives us a new way to identify it to make this technology more clinically useful for us.” – by Abigail Sutton
Reference:
Feldman RM. Primary angle closure glaucoma, a bigger problem than you think. Presented at: Optometric Glaucoma Society annual meeting; San Antonio; November 6, 2018.
Disclosure: Feldman is a consultant for Allergan, Valeant and Aerie.