Steady, Low Intraocular Pressure Best to Preserve Visual Field in Glaucoma

SEOUL, South Korea, Aug. 13 -- Fluctuations in intraocular pressure may increase the risk of visual field deterioration in glaucoma patients even if they are able to maintain pressures below 18 mm/Hg, researchers found.

In patients who achieved intraocular pressure below that level, progressive visual field deterioration was significantly more common among those whose pressures fluctuated by more than two standard deviations without crossing the 18 mm/Hg threshold (P<0.001), wrote Samin Hong, M.D., of Yonsei University College of Medicine here, in the August issue of Archives of Ophthalmology.

"Our results suggest that glaucomatous visual field damage cannot be stabilized by only lowering the postoperative IOP but also requires reducing the long-term fluctuation of the post-operative IOP," he said.

Dr. Hong and colleagues studied 408 patients who had undergone phacoemulsifcation, posterior chamber intraocular lens implantation, and trabeculectomy to lower intraocular pressure.

Measurements of intraocular pressure and visual field were taken at three months, six months, and yearly after surgery for 13 years. Patients were divided into two groups -- those whose intraocular pressure fluctuated by less than two standard deviations (group 1) and those whose pressures fluctuated by more than two standard deviations (group 2).

The study included 246 patients with primary open-angle glaucoma and 162 with chronic primary angle-closure glaucoma. The mean follow-up was 9.2 years. All patients maintained intraocular pressure at less than 18 mm/Hg throughout follow-up.

Sixty of the primary open-angle glaucoma patients and 42 of the chronic primary angle-closure glaucoma patients had fluctuations of more than two standard deviations during follow-up.

There was no significant difference in visual field defect scores among patients whose pressure was stable during follow-up, but "the number of patients with progressive [visual field] loss was significantly higher in group 2 (30.0% for [primary open-angle glaucoma]; 28.6% for [chronic primary angle-closure glaucoma]) than in group 1" (9.7% and 10.0%, respectively), they wrote.

In an accompanying editorial Joseph Caprioli, M.D., of the Jules Stein Eye Institute, UCLA, theorized that long-term fluctuation in intraocular pressure might disrupt homeostatic mechanisms.

"Irregular and large [intraocular pressure] fluctuations may cause a loading and unloading of stresses, and as opposed to conditions of static stress, the tissue is unable to compensate and damage occurs," Dr. Caprioli wrote.

The study by Hong and colleagues, suggests that modulation of pressure rather than its reduction might be an appropriate treatment for glaucoma, he wrote.

He pointed out that "the main disadvantage of the study is its retrospective nature with all the typical attendant biases."

Specific guidelines for intraocular pressure modulation "must await a better understanding of the pathophysiologic consequences of [pressure] fluctuation in glaucoma," Dr. Caprioli concluded.