'Seeing' Hypertension

Blood vessels in the eyes may warn of high blood pressure

The tiniest blood vessels of the eye may signal big problems to come, in the form of future high blood pressure.

That finding from Australian researchers comes from an experimental technique -- a computerized analysis of special camera /images of the retina, Dr. Paul Mitchell, a professor of ophthalmology at the University of Sydney and co-author of a study on the technique, told HealthDay .

The technique actually is an advanced version of the everyday eye examination that cardiologists use, co-author Jie Jin Wang, a senior research fellow at the university, said. "Your cardiologist uses an ophthalmoscope to examine your retina, the back of your eye, as the retinal circulation is an extension of the brain's circulation," Wang told HealthDay . "The retina is the only site in our bodies at which vessels can be seen naked."

But that examination detects changes or damage only in the larger retinal blood vessels, Wang said. The Australian trial used computer software that was developed at the University of Wisconsin-Madison and could detect narrowing of the tiniest blood vessels, called arterioles, with an average diameter of about 200 microns. (A micron is one-millionth of a meter.)

A five-year study of more than 3,600 Sydney residents showed that narrowing of arterioles is a good indicator of a person having severe high blood pressure in the future, the researchers reported.

The study followed 1,319 people with normal or high-normal blood pressure. Five years later, 390 had severe high blood pressure. Retinal arterioles that had narrowed predicted the development of severe high blood pressure no matter how old the participant was, but "the association was even stronger in patients younger than 65," the researchers said.

Despite the findings, it's too soon to say whether people with normal blood pressure but narrowed arterioles should be treated, Mitchell said.

The issue of pre-treatment "is an interesting area for a trial," he said. "However, we need more information about the natural history and time course of these changes before such a trial could start. Such information is currently being collected in our study and in the U.S. studies that have used these techniques."

Experts don't know why narrowing of retinal blood vessels can predict high blood pressure, he said. One theory is that reactions to even moderate narrowing of blood vessels are inherited genetically, which lead to a "vicious circle," Mitchell explained.

"In responding to low-level elevated blood pressure, small vessels may constrict, leading to increased blood flow resistance and further blood pressure elevation," he said.

People are considered to have hypertension when their systolic blood pressure (the top number) is consistently over 140 and their diastolic blood pressure (bottom number) is consistently over 90, according to the National Institutes of Health.