Cataract surgery: Benefits on IOP more significant than realized

Instead of combined surgery, cataract extraction alone by phacoemulsification through a clear corneal incision with posterior chamber IOL implantation may be the most appropriate procedure for patients with controlled or modestly uncontrolled glaucoma as well as for patients with ocular hypertension or glaucoma suspects, said Richard L. Lindstrom, MD, in his delivery of the Kelman Lecture during the Spotlight on Cataract Surgery session of the annual meeting of the American Academy of Ophthalmology.

"It may be that a lot of adult glaucoma is 'phacomorphic,' and perhaps the best therapy is to remove the crystalline lens," said Dr. Lindstrom, founder and attending surgeon, Minnesota Eye Consultants, Minneapolis. "Phacoemulsification, Charles Kelman's extraordinary gift to the cataract surgeon and patient, may be an equally important blessing for the glaucoma surgeon and patient."

Although IOP reduction after cataract surgery has been a long-recognized phenomenon, Dr. Lindstrom presented evidence that the lowering achieved in eyes presenting with higher levels of IOP is much greater than realized.

To investigate the effect of cataract surgery on IOP, he undertook retrospective analyses, pooling eyes from two practices. Two series of eyes were considered-one composed of ocular hypertensives and glaucoma suspects (588 eyes) and the other including eyes diagnosed with glaucoma (124 eyes). In both groups, the amount of IOP reduction after cataract surgery was found to be proportional to the presurgical IOP and quite significant in those at the higher end of the spectrum.

In the first cohort, eyes with an IOP ranging from 23 to 31 mm Hg experienced an average 7 mm Hg drop that was present at follow-up of 1 and 10 years. In the second group, eyes with the highest levels of IOP (23 to 29 mm Hg) experienced an average 9 mm Hg IOP reduction that also persisted with the same duration of follow-up.

To investigate the effect of cataract surgery on IOP further, Dr. Lindstrom undertook a literature review with Brooks Poley, MD, in which eyes from previously reported papers were stratified based on their presurgical IOP. Consistent with his own retrospective analyses, the results showed that in eyes with higher IOP (i.e., those in need of IOP reduction), average decreases of at least 8 to 10 mm Hg were achieved.

Additional evidence of the benefit of phacoemulsification on elevated IOP derives from an analysis of conversion rates of ocular hypertension to glaucoma after cataract surgery. Dr. Lindstrom reported that the outcomes of his patient series compared very favorably with data reported in the Ocular Hypertension Treatment Study.

"In our series during an average follow-up of 4.1 years, the conversion rate was only 1.1% using a rigorous definition that included any patient started on topical IOP-lowering therapy," he said. "We had no patients who developed visual field loss."

Dr. Lindstrom explained the anatomic basis by which the aging lens can increase IOP, and demonstrated the mechanism using optical coherence tomography and MRI images from published studies.

"Perhaps as patients develop elevated IOP and we are getting ready to treat that finding, we should consider if they might have an indication for lens removal, including early cataract, significant refractive error, or dissatisfaction because of presbyopia, and offer these patients the option of our fantastic operation of phacoemulsification with a posterior chamber IOL," Dr. Lindstrom concluded.