Cataract surgery can dramatically lower elevated IOP, and the effect appears to be quite durable. This benefit, together with the safety of phacoemulsification, suggests that ophthalmologists should consider its role as a stand-alone procedure to treat co-morbid cataract and glaucoma.
"It may be that a lot of adult glaucoma is 'phacomorphic,' and perhaps the best therapy is to remove the crystalline lens. Phacoemulsification, Charles Kelman's extraordinary gift to the cataract surgeon and patient, may be an equally important blessing for the glaucoma surgeon and patient," said Dr. Lindstrom, founder and attending surgeon, Minnesota Eye Consultants, Minneapolis.
Although IOP reduction after cataract surgery has been a long-recognized phenomenon, Dr. Lindstrom presented evidence that the lowering of pressure achieved in eyes presenting with higher levels of IOP is much greater than previously realized.
To investigate the effect of cataract surgery on IOP, he undertook retrospective analyses, pooling data from eyes operated on at his own practice and by Richard Schulze Sr., MD, and Richard Schulze Jr., MD, in their practice in Savannah, GA.
Two series of eyes were considered: one consisting of those with ocular hypertension and suspected glaucoma (588 eyes) and the other including eyes in which glaucoma had been diagnosed (124 eyes). Eyes included in the first series had elevated or normal IOP and no history of any glaucoma medical therapy or glaucoma surgery, including laser surgery. Patients with glaucoma were defined as individuals receiving IOP-lowering drops, having a history of glaucoma surgery and/or laser trabeculoplasty, or having evidence of visual field or optic nerve defects consistent with glaucomatous damage.
IOP at the time of cataract surgery ranged from 9 to 31 mm Hg among those with ocular hypertension or suspected glaucoma and from 5 to 29 mm Hg in the patients with glaucoma. Follow-up for each group ranged from 1 to 10 years with a mean of 4.5 years.
In each series, patients were stratified into five groups according to their IOP at the time of cataract surgery.
Analyses of changes from pre-cataract surgery IOP showed that in both those with ocular hypertension or suspected glaucoma and in those with glaucoma, mean IOP was lower at 1 and 10 years of follow-up in all subgroups except in those with the lowest baseline IOPs (9 to 14 mm Hg and 5 to 14 mm Hg), whose increase was minimal. The amount of IOP reduction after cataract surgery was unrelated to age, proportional to the pre-surgical IOP within each patient series, relatively greater in the patients with glaucoma than in those with ocular hypertension or suspected glaucoma per IOP tier, and quite significant in both series for eyes at the higher end of the baseline IOP spectrum.
Among those with ocular hypertension or suspected glaucoma, eyes with an IOP ranging from 23 to 31 mm Hg before cataract surgery experienced an average 7 mm Hg drop after 1 year that persisted to 10 years. In the patients with glaucoma, eyes in the highest IOP subgroup (23 to 29 mm Hg) experienced an average 9 mm Hg IOP reduction that also persisted with the same duration of follow-up, Dr. Lindstrom reported.
To investigate further the effect of cataract surgery on IOP, Dr. Lindstrom said he undertook a literature review with Brooks Poley, MD, in which eyes from previously reported papers were stratified based on their pre-surgical IOP.
Consistent with his own retrospective analyses, the results showed that in eyes with higher IOP (those in need of IOP reduction), average decreases of at least 8 to 10 mm Hg were achieved.
As additional evidence of the benefit of phaco on elevated IOP, Dr. Lindstrom presented an analysis of conversion rates of ocular hypertension to glaucoma after cataract surgery. He reported that the outcomes of his patient series compared very favorably with data reported in the Ocular Hypertension Treatment Study (OHTS). In OHTS, 9.5% of patients with untreated ocular hypertension and 4.4% of those randomly assigned initially to treatment progressed to glaucoma after follow-up of 5 years.