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TUESDAY, Aug. 10 (HealthDayNews) -- The tiniest blood vessels of the eye can provide a glimpse that may warn of future high blood pressure, Australian researchers report.

That finding comes from a computerized analysis of special camera images of the retina, an experimental technique that is "not immediately applicable to clinical practice, but has the potential to be used in the future," said Dr. Paul Mitchell, a professor of ophthalmology at the University of Sydney and co-author of a study on the technique in the Aug. 10 issue of Hypertension.

It is a highly advanced version of the eye examination that cardiologists use routinely, explained study co-author Jie Jin Wang, a senior research fellow at the university.

"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 said. "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 computer software used in the Australian trial, which was developed at the University of Wisconsin-Madison, was able to detect narrowing of the smallest blood vessels, called arterioles, whose average diameter is about 200 microns. (A micron is one-millionth of a meter.)

And a five-year study of more than 3,600 Sydney residents showed that narrowing of arterioles on that exquisitely small scale was a powerful harbinger of future severe high blood pressure, the researchers report.

The study followed 1,319 participants who had normal or high normal blood pressure. Five years later, 390 had severe high blood pressure. Narrowed retinal arterioles predicted the development of severe high blood pressure regardless of age, but "the association was even stronger in patients younger than 65," the researchers reported.

It's too early to say whether such changes should prompt treatment of people with normal blood pressure but narrowed arterioles, 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," Mitchell said. "Such information is currently being collected in our study and in the U.S. studies that have used these techniques."

It's not known why narrowing of retinal blood vessels can predict high blood pressure, he said. There are several theories, one of which says that there are genetically determined reactions to even moderate narrowing of blood vessels.

"This could be a vicious circle," Mitchell said. "In responding to low-level elevated blood pressure, small vessels may constrict, leading to increased blood flow resistance and further blood pressure elevation."

More information

To see the blood vessels of your retina, follow the do-it-yourself instructions from the Exploratorium.

(SOURCES: Paul Mitchell, M.D., Ph.D., professor, ophthalmology, University of Sydney, Australia; Jie Jin Wang, Ph.D., senior research fellow, University of Sydney, Australia; Aug. 10, 2004, Hypertension)

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