Surgeon elucidates theories on why phaco reduces IOP
NEW ORLEANS — Phacoemulsification reduces IOP in glaucomatous and non-glaucomatous eyes, although clinicians are not certain about the underlying causes, a surgeon said here.
During Glaucoma Subspecialty Day preceding the American Academy of Ophthalmology meeting, Douglas J. Rhee, MD, OSN Glaucoma Board Member, discussed theories that may explain how phacoemulsification reduces IOP.
“The conventional wisdom had been that pressure is usually reduced by about 1 mm Hg to 4 mm Hg, and this can be sustained for about 3 to 5 years,” Rhee said.
Douglas J. Rhee
According to a study comparing phacoemulsification alone and combined with implantation of the iStent (Glaukos), eyes undergoing phacoemulsification alone had preoperative IOP of 25.4 mm Hg and IOP was reduced by almost 9 mm Hg.
Study data show that reduced IOP can be attributed to enhanced trabecular meshwork outflow, not increased scleral outflow, Rhee said.
Although phacoemulsification reduces IOP, there is no alteration of circadian fluctuation of IOP, except in some eyes with pseudoexfoliation, Rhee said.
“You’d think that it might [cause a circadian fluctuation of IOP] because most interventions like laser or other surgical procedures will actually flatten out the diurnal curve,” he said. “Phaco does not.”
One laboratory found increased interleukin levels in trabecular meshwork endothelial cells of glaucomatous eyes exposed to ultrasound, Rhee said. Interleukin-1a is a stress hormone and pathologic marker for primary open-angle glaucoma, he said.
Disclosure: Rhee has financial relationships with Alcon, Allergan, AqueSys, Merck and Santen.