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November 3, 1999
UI study adds evidence: Common glaucoma treatment may contribute to other eye risks
IOWA CITY, Iowa -- Beta-blocker eyedrops, commonly used to treat glaucoma, may put some people with the condition at increased risk for further visual loss by aggravating the fall of blood pressure during sleep, according to a University of Iowa Health Care study.
This excessive nighttime fall in blood pressure in susceptible individuals can interfere with optic nerve circulation which, in turn, may worsen glaucoma damage and produce an optic nerve stroke, known as anterior ischemic optic neuropathy, said Sohan Singh Hayreh, M.D., Ph.D., D.Sc., UI professor emeritus of ophthalmology and visual sciences, and lead author.
"Blood pressure normally falls during sleep in all of us, and it is not a problem if there are no other risk factors," Hayreh said. "However, if a person with glaucoma is taking beta-blocker eyedrops to lower eye pressure, the blood pressure could fall even more and potentially reduce blood circulation through the optic nerve in susceptible individuals."
Although these beta-blocker eyedrop side effects had been previously documented, the UI planned study is the first to examine the problem on a large-scale by continuous blood pressure monitoring over a 24-hour period. The UI team studied 275 white patients, 161 with glaucoma and 114 who had experienced an eye stroke. The participants had their blood pressure monitored every 10 minutes during the daytime and every 20 minutes during the nighttime for 24 hours.
"We were surprised to find that patients with normal tension glaucoma, also known as low tension glaucoma, had much greater decreases in blood pressure than patients who were known to have the optic nerve stroke," Hayreh said.
Patients using beta-blocker eyedrops had much greater decreases in nighttime diastolic blood pressure, lower minimum nighttime diastolic blood pressure, and lower minimum nighttime heart rate than patients who were not using the medication. Thus, beta-blocker eyedrop use may put individuals at risk for optic nerve stroke or worsened glaucoma damage.
Previous studies led by Hayreh have shown a significant association between progressive vision deterioration and nighttime blood pressure fall in patients with glaucoma or optic nerve stroke who also had high blood pressure and were on blood pressure lowering medication.
Beta-blockers are one of many types of pills used to lower high blood pressure. The UI studies seem to suggest that beta-blockers taken orally as a pill or in eyedrop form can cause excessive blood pressure fall during sleep, particularly when the medication is taken at bedtime or in the evening. The excessive blood pressure decrease is then a risk factor for glaucoma damage or optic nerve stroke. These risks also hold true for other blood pressure-lowering medicines.
Lowering the eye pressure in people with glaucoma is absolutely essential to prevent visual loss. Beta-blocker eyedrops lower the eye pressure very effectively in the vast majority of people; hence, their use since the early 1970s has become almost the first option for glaucoma treatment, Hayreh said.
"It is absolutely essential for people with glaucoma to lower their eye pressure," he said. "However, the present research study suggests that for some individuals beta-blocker eyedrops may not be the ideal medication to use.
"If a person with glaucoma is using beta-blocker eyedrops and yet is still losing vision in spite of low eye pressure, the nighttime blood pressure decrease may be the underlying factor. In that case, it is better to switch to other glaucoma drops that do not decrease the blood pressure too much during sleep."
Hayreh cautioned that people using beta-blockers, whether in eyedrop form for glaucoma or pill form for high blood pressure, should not stop taking their medication on their own because that can be extremely dangerous. Instead they should consult with their ophthalmologist or other physician about whether they are at increased risk for problems and should thus adjust their treatment.
Approximately 2 million Americans have glaucoma. Overall, it is the second most common cause of legal blindness. Glaucoma painlessly destroys side vision, thus limiting a person's ability to perform most day-to-day activities such as walking, driving or carrying out manual tasks. A person with glaucoma can deceptively believe that his or her eyes are fine because central vision is generally lost only in the late stages of the disease. Left untreated, glaucoma damage is irreversible and progressive, ultimately resulting in complete blindness.
Optic nerve stroke is one of the most common causes of sudden visual loss in the middle-aged and elderly population. Haryeh first postulated the connection between optic nerve strokes and blood pressure fall during sleep in 1974. He reported in 1998 that three of every four patients who had an optic nerve stroke noticed sudden loss of vision after they had slept. The recent 24-hour blood pressure monitoring study lends support to the connection between eye stroke and nighttime blood pressure decreases.
The UI findings on beta-blocker eyedrops and glaucoma were published in the September issue of the American Journal of Ophthalmology.
The UI team also included Patricia Podhajsky, a research nurse in ophthalmology and visual sciences, and M. Bridget Zimmerman, Ph.D., a biostatician in the UI College of Public Health.
The study was supported by grants from the National Institutes of Health, and Research to Prevent Blindness, Inc. based in New York. Hayreh is also a Research to Prevent Blindness Senior Scientific Investigator.
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11/03/99
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