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UI research: Risk of vision loss caused by nighttime fall of blood pressure

IOWA CITY, Iowa -- Researchers in the University of Iowa College of Medicine are concerned that people who take medications to control high blood pressure at bedtime or in excessive amounts may be at increased risk for an eye disorder known as anterior ischemic optic neuropathy (AION) or stroke of the eye.

According to Dr. Sohan Hayreh, professor of ophthalmology and the lead author of the study published in the American Journal of Ophthalmology, AION seems to have become increasingly common since the introduction of powerful new blood pressure medications.

The research indicates that in three-quarters of all AION cases, the precipitating factor is a drop in blood pressure during the night, the clue that led Hayreh and his team to investigate the relationship between the drugs and the condition.

AION is a condition brought on by a small stroke of the optic nerve, the result of diminished blood supply to the anterior, or front part, of the optic nerve. AION may cause serious vision impairment.

Some people with AION may not immediately realize their vision has been affected. "I had one patient recently who did not discover his impairment until he went hunting and tried to aim his gun," Hayreh says.

Hayreh says that 25 percent of those who have an incident in one eye develop AION in the other eye within three years. "One day you are functioning fine and within a few weeks, you have a serious visual disability," he says.

In their study, the researchers looked at 925 episodes of the onset of AION to determine the time of day and the season of the year in which persons with the condition discovered their visual loss. More than three-quarters of the people reported they discovered their impairment upon waking, either from a night's sleep or from a nap.

Hayreh, who first described and named the condition in 1974, had previously made the connection between the onset of AION and a decrease in blood pressure during sleep. Blood pressure normally drops when a person is asleep. By using a small blood pressure monitor developed in the last decade, Hayreh has recorded steep drops in blood pressure among those who had AION and glaucoma. He found that patients taking such medications as beta-blockers, calcium channel blockers and ACE inhibitors, all of which have become popular treatments for hypertension and other heart conditions in recent years, suffered significantly more optic nerve damage.

Hayreh notes that some medications prescribed for enlarged prostate can also result in significant drops in blood pressure during the night. "This is cause for concern, since urologists who treat the prostate condition may not be aware of the increased risk for AION," he says.

Hayreh says that in addition to the medications, risk factors for AION include diabetes, smoking, high blood pressure and high cholesterol levels.

The researchers also found that onset of AION occurs significantly more often during warm months. Hayreh says this indicates that a different set of factors may be at work to cause AION than those that precede heart attack and stroke in the brain, both of which are more common during the winter.

"We have found no evidence that patients with AION are at increased risk for heart attack or stroke in the brain," he says. "The fact that AION is more common during warm weather is something that we cannot yet explain. More research is needed."