Fluctuations in eye pressure may be associated with a decreasing peripheral field of vision in patients with glaucoma, even if their eye pressure remains low overall, according to a report in the August issue of Archives of Ophthalmology, one of the JAMA/Archives journals.
"Prevention of further visual field deterioration is a goal of glaucoma therapy," the authors write as background information in the article. "Previous studies reported that lowering intraocular pressure (IOP) slowed the advancement of visual field damage in patients with glaucoma. However, even if the IOP can be substantially lowered, reduction of mean [average] and peak IOP does not always prevent progressive visual field deterioration."
Samin Hong, M.D., and colleagues at the Yonsei University College of Medicine, Seoul, Korea, studied 408 eyes of patients (average age 66.5 years) who had undergone a triple procedure to treat glaucoma: phacoemulsification, that involves dissolving and removing the lens; posterior chamber intraocular lens implantation; and trabeculectomy, also known as filtration surgery. All patients had a low IOP after surgery (below 18 milligrams of mercury). Measurements of IOP and visual field were taken for an average of 9.2 years following surgery. Based on the standard deviation (difference from the average) in IOP, the eyes were split into two groups, one with greater fluctuation and one with less.
Throughout the follow-up period, the two groups had the same average IOP, and their visual fields were the same after three months. However, after the last follow-up examination--13 years later--the visual field was significantly worse in the group with greater fluctuation in IOP. The number of patients with progressive visual field loss was significantly larger in the group with more fluctuation.
"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," the authors conclude.(Arch Ophthalmol. 2007;125(8):1010-1013. Available pre-embargo to the media at www.jamamedia.org.)
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Editorial: Pressure Modulation May Help Preserve Vision Fluctuations in IOP have been pinpointed as a potential cause for glaucoma and a factor in worsening the eye damage caused by the disease, writes Joseph Caprioli, M.D., of the Jules Stein Eye Institute, UCLA, in an accompanying editorial.
"Why should IOP fluctuation be damaging" Theories abound about the mechanisms of retinal ganglion cell damage in glaucoma, but no single cellular or molecular cause satisfactorily explains the condition in all patients," Dr. Caprioli writes. "Long-term variability may disrupt homeostatic mechanisms. Irregular and large IOP 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."
"I would propose for your consideration 'IOP modulation' rather than 'IOP reduction' as appropriate treatment," he concludes. "This would not only lead to robust IOP reduction in patients with advancing disease but also establish the goal of reducing IOP fluctuation, particularly in patients with disease progression even at lower pressures. Specific guidelines, however, must await a better understanding of the pathophysiologic consequences of IOP fluctuation in glaucoma."
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