Have Researchers Identified an Early Predictor for Glaucoma?

photograph of retina showing glaucomatous cupping of the optic disc

A new study, published in the January 2013 issue of Ophthalmology, concludes that blood vessel changes within the eye could be an early warning sign of an increased risk for glaucoma. Ophthalmology, the official journal of the American Academy of Ophthalmology, publishes original, peer-reviewed reports of research in ophthalmology, including treatment methods, the latest drug findings, and results of clinical trials.

The Study Authors

The study, entitled Retinal Vessel Caliber Is Associated with the 10-year Incidence of Glaucoma: The Blue Mountains Eye Study, was authored by Ryo Kawasaki; Jie Jin Wang; Elena Rochtchina; Anne J. Lee; Tien Yin Wong; and Paul Mitchell, who represent the following institutions: Centre for Eye Research, University of Melbourne; Centre for Vision Research, University of Sydney; Yamagata University Faculty of Medicine, Japan; Osaka Medical Center for Health Science and Promotion, Japan; and National University of Singapore. (Note: The term “caliber,” in this context, describes the internal diameter of a retinal blood vessel.)

About the Blue Mountains Eye Study

The longitudinal Blue Mountains Eye Study (BMES), named after the Australian mountain range, is the first large population-based assessment of visual impairment and common eye diseases of a representative sample of older Australians. A longitudinal study follows, and gathers information about, the same individuals or group of people over an extended period of time – often many decades.

The ongoing BMES began in 1992-1993, with the recruitment of 3,654 people aged 50 and older. Follow-up exams were conducted in 1997-1999 (5-year), 2002 (10-year) and 2007-2009 (15-year). More than 150 publications have resulted from BMES data. You can read more about the BMES at the University of Sydney’s Centre for Vision Research.

About the Research and Glaucoma

The objective of the study was to examine associations, in subjects enrolled in the BMES, between measurements of the internal diameter of retinal blood vessels and the 10-year incidence of primary open-angle glaucoma.

Glaucoma is a group of eye diseases that damage the optic nerve and is one of the leading causes of vision loss and blindness. Open-angle glaucoma is the most common form of glaucoma.

The eye continuously produces a fluid, called the aqueous (or aqueous humor), that must drain from the eye in order to maintain healthy eye pressure. Aqueous humor is a clear, watery fluid that flows continuously into, and out of, the anterior chamber of the eye, which is the fluid-filled space between the iris and the cornea. It is the aqueous that helps to bring nutrients to the various parts of the eye.

Aqueous fluid drains from the anterior chamber through a filtering meshwork of spongy tissue along the outer edge of the iris (the trabecular meshwork), where the iris and cornea meet, and into a series of tubes, called Schlemm’s canal, that drain the fluid out of the eye. Problems with the flow of aqueous fluid can lead to elevated pressure within the eye.

In primary open-angle glaucoma, the filtering meshwork may become blocked or may drain too slowly. If the aqueous fluid cannot flow out of the eye, or flow out quickly enough, pressure builds inside the eye and can rise to levels that may damage the optic nerve, resulting in vision loss.

More About the Research

From a study summary in Science Codex:

Using diagnostic photos and other data from the Australian Blue Mountains Eye Study, the researchers showed that patients who had abnormally narrow retinal arteries when the study began were also those who were most likely to have glaucoma at its 10-year end point. If confirmed by future research, this finding could give ophthalmologists a new way to identify and treat those who are most vulnerable to vision loss from glaucoma.

The findings of the new study, led by Paul Mitchell, M.D., PhD, supports the concept that abnormal narrowing of retinal blood vessels is an important factor in the earliest stages of open-angle glaucoma (OAG). Tracking nearly 2,500 participants, the study found that the OAG risk at the 10-year mark was about four times higher in patients whose retinal arteries had been narrowest when the study began, compared with those who had had the widest arteries.

Compared with the study group as a whole, the patients who were diagnosed with OAG by the 10-year mark were older, had had higher blood pressure or higher intraocular [i.e., within the eye] pressure at the study’s baseline, and were more likely to be female.

“Our results suggest that a computer-based imaging tool designed to detect narrowing of the retinal artery [diameter] could effectively identify those who are most at risk for open-angle glaucoma,” said Dr. Mitchell. “Such a tool would also need to account for blood pressure and other factors that can contribute to blood vessel changes. Early detection would allow ophthalmologists to treat patients before optic nerve damage occurs and would give us the best chance of protecting their vision.”

Limitations of the Study

The study authors advise caution when interpreting the results, however, stating that because glaucoma takes so long to develop, it remains unclear if these retinal blood vessel changes are part of the cause of the disease or part of its normal progression. Further studies are required to fully understand the exact role of retinal blood vessel changes in the development and progression of glaucoma.

VisionAware will continue to provide updates for this ongoing glaucoma research, as well as updates of the Blue Mountains Eye Study, as they become available.

Glaucoma Awareness Month

According to the American Academy of Ophthalmology (AAO), a symptomless eye disease like glaucoma highlights the importance of regular eye exams. AAO recommends that everyone have a complete eye exam by an ophthalmologist at age 40 and stick to the follow-up exam schedule advised by his or her doctor.

This January, during Glaucoma Awareness Month, the Academy encourages people to learn more about the disease known as “the sneak thief of sight.” People who have a family history of glaucoma, or who are African-American or Hispanic, may be at higher risk. For more information on glaucoma, its risk factors, and treatment options, visit Glaucoma: An Overview at VisionAware.org and What Is Glaucoma? from the Academy’s EyeSmart website.