"Living cells in the eye lens do not have blood," he said. "Oxygen is delivered by the aqueous humor. The theory is that beta-blockers reduce production of aqueous humor and so reduce delivery of oxygen to the lens, so the lens ages prematurely. This article seems to find further evidence of that."
But the final verdict on the beta-blocker/cataract link is far from certain, Budenz stressed. "There are studies showing no effect of glaucoma drugs on cataract formation," he noted.
The widespread use of beta-blockers should not be affected by the finding because glaucoma is a more direct -- and less treatable -- cause of vision loss than cataract formation, Budenz said.
Cataracts form slowly, he said. "Most people who have cataracts would need surgery eventually," Budenz said. "If there were sure evidence that beta-blockers hasten their development, that would not factor into our algorithm for treating glaucoma."
Cataract surgery, in which the clouded lens is replaced by a clear, artificial lens, can be done in a matter of hours, usually without a hospital stay, he noted.
"I really don't think that this study would affect patient care at this moment unless stronger evidence came out linking the two," said Dr. Vatinee Bunya, assistant professor of ophthalmology at the University of Pennsylvania Scheie Eye Institute.
The finding "should be taken with a degree of caution," she said. "We definitely need more studies."
Anyway, Bunya said, "topical beta-blockers are not the first line of glaucoma treatment for most practitioners. I don't think many ophthalmologists would change their practice based on this."
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