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IOP reduction sustained after cataract surgery
Study results show that cataract surgery alone might be sufficient to reduce IOP in most eyes with ocular hypertension and controlled glaucoma.
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Cataract extraction without IOP-lowering medications yielded a significant, sustained reduction in pressure, according to data culled from the Ocular Hypertension Treatment Study.
The results underscored the efficacy of cataract surgery alone in lowering IOP in some eyes, Steven L. Mansberger, MD, MPH, the corresponding study author, told Ocular Surgery News.
“The point of our paper is that some patients may have enough IOP lowering with cataract surgery alone, especially [those] with ocular hypertension,” Mansberger said. “Those with well-controlled glaucoma, those who only have ocular hypertension or are glaucoma suspects, may only need cataract surgery alone to attain a lower intraocular pressure.”
The Ocular Hypertension Treatment Study (OHTS) included 1,636 patients. It was designed to gauge the safety and efficacy of IOP-lowering medication in preventing the onset of primary open-angle glaucoma in patients with elevated IOP. Patients were randomized to receive IOP-lowering medication or undergo observation.
The study was published in Ophthalmology.
Patients and protocols
Mansberger and colleagues included data from the observation group of the OHTS and excluded data from the medication group. Their comparative case series included 63 eyes of 42 patients who underwent cataract extraction. A control group comprised 743 eyes of 743 subjects who did not have cataract surgery.
Mean patient age was 64.1 years in the cataract surgery group and 55 years in the control group.
Steven L. Mansberger
The researchers determined a split date: a point at which cataract surgery was reported in the study group and a corresponding date in the control group.
IOP was measured up to three times before the split date and up to three times after the split date in both groups.
Mean preoperative IOP in the surgery group was 23.9 mm Hg. In the control group, mean IOP before the split date was 23.8 mm Hg.
Mean central corneal thickness was 584.7 µm in the study group and 574.3 µm in the control group.
“We don’t know why this difference occurred. Perhaps this represents a bias towards surgery in those with a thicker cornea because they had a higher pressure, and that encouraged them or their doctor to have cataract surgery,” Mansberger said. “However, it was only a 10-µm difference, so it’s really a small difference in terms of corneal thickness and could simply be a chance difference between the groups. Otherwise, the amount of IOP lowering should be valid since corneal thickness was not related to IOP lowering in our study.”
Results and conclusions
Study results showed that mean postoperative IOP in the surgery group was 19.8 mm Hg; the decrease was statistically significant (P < .001).
The average decrease in IOP after surgery was 16.5%; postoperative IOP was at least 20% lower than preoperative IOP in 39.7% of eyes.
In the surgery group, postoperative IOP was lower than preoperative IOP for at least 36 months.
Mean IOP in the control group was 23.8 mm Hg before the split date and 23.4 mm Hg after the split date; the decrease was not statistically significant.
The greatest reduction in postoperative IOP occurred in eyes with the highest preoperative IOP, Mansberger said.
“That was something shown by our paper and was in agreement with other people’s papers as well,” he said. “That was really the main factor associated with IOP lowering.”
Data on complications were not available, Mansberger said.
“If we had the ability to exclude those that may have had complications from cataract surgery, we may have had an even lower intraocular pressure. However, by presenting the data as an ‘intention-to-treat’ analysis, the results are more generalizable,” he said. – by Matt Hasson
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Perspective
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Thomas W. Samuelson, MD, MD
Hopefully, amid the avalanche of manuscripts, marketing materials, e-blasts, newsletters and unsolicited correspondence that we all receive daily, this article by Mansberger and colleagues was noticed by those who treat patients with glaucoma. This is an important paper. It applies the scientific and statistical rigor inherent to a tightly controlled NEI clinical trial to the often-perplexing debate concerning the effect of phacoemulsification on IOP. Most recently published articles on this subject suggest that phacoemulsification lowers IOP in most patients in whom the preoperative IOP is elevated beyond physiological levels. Meanwhile, a recent paper by Chang and colleagues concluded that there was no such IOP-lowering effect of phacoemulsification when compared with a control group comprised of the unoperated fellow eyes of patients subjected to unilateral cataract extraction. So which is correct? In my opinion, one article does not have to be wrong for the other to be right. The Mansberger article, reporting sustained IOP reduction among patients in the Ocular Hypertension Treatment Study following phacoemulsfication, is consistent with my own experience and publications. While at first glance the Chang article appears at odds with this conclusion, a more detailed assessment of the articles reveals that the two studies are not comparable. While the preoperative IOP in the Mansberger article was 23.9 mm Hg, the average preoperative IOP in the Chang paper was 15.66 mm Hg. Further, the Chang article is confounded by the use of medications preoperatively and postoperatively. No information is provided whether an attempt was made to discontinue medications postoperatively. I believe that the Chang article supports what many have reported: When the preoperative IOP is physiological, little if any IOP reduction occurs following phacoemulsification. However, when the preoperative IOP is elevated, as was the case in the OHTS paper by Mansberger and coauthors, many patients experience meaningful IOP reduction. The OHTS investigators have provided yet another important and clinically meaningful finding from this landmark trial, specifically, the cleanest data to date showing that phacoemulsification lowers IOP in a meaningful percentage of patients with elevated IOP. Hopefully we noticed.
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