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Health

Glaucoma: The 'silent thief' begins to tell its secrets
Scientists look into the mystery of why millions lose their sight
 
Published Wednesday, February 19, 2014
by National Eye Institute

PHOTO/MICROSOFT IMAGES
A lot remains unknown about glaucoma, the world's number one cause of blindness. The disease is often called the "silent thief of sight."

Glaucoma is sometimes called the "silent thief of sight" because of the stealthy manner in which it progresses.

Glaucoma slowly damages the eyes overtime, often causing serious irreparable harm without symptoms or any loss of vision.

Glaucoma is the world’s leading cause of blindness, and while there are treatments to delay vision loss, there is no cure. In fact, researchers have yet to pinpoint a specific cause in most cases.

The disease, which attacks the optic nerve, the cable that connects the eyes to the brain, affects more than 2.7 million people in the United States and more than 60 million worldwide. There are many forms, but the most common and most mysterious is open-angle glaucoma.

"Primary open-angle glaucoma remains a black box, but researchers are pursuing many avenues to investigate the underlying causes," said Hemin Chin, Ph.D., director of the Glaucoma and Optic Neuropathies program at the National Eye Institute, part of the National Institutes of Health. “As we develop a better understanding of the disease process, we hope this will lead to new, more effective treatments and possibly even preventive therapies for it.”

High-pressure research

If you've ever had an air-puff test, also known as tonometry, then you may have heard that glaucoma is linked to an increase in eye pressure, or intraocular pressure. The unique anatomy of the eye, when combined with other factors, can cause a rise in eye pressure that can in turn cause some types of glaucoma.

When this happens, the eye fills with fluid that drains through a gap between the cornea and iris. This build-up of fluid and eye pressure can damage the optic nerve.

The front of the eye, between the cornea (the eye's front window) and the iris (the colored part of the eye), is filled with a clear fluid. This fluid leaves the eye and enters the blood by passing through a gap at the angle where the cornea and iris meet. The gap is filled with a sponge-like tissue called the trabecular meshwork, which helps regulate fluid passage. Sometimes, eye infections, injuries, or certain medications can narrow the gap and compress this spongy tissue, producing a rapid buildup of fluid and eye pressure. This is called angle-closure glaucoma.

In the United States, open-angle glaucoma is more common than angle-closure glaucoma, affecting about three times as many people. It has a more gradual course and there are no clear signs of blockage within the eye's drainage system. Yet, researchers estimate that 50 to 80 percent of people with open-angle glaucoma have eye pressure that is higher than average. Others have normal pressure or even low pressure. On the flip side, many people have high eye pressure but never develop glaucoma.

"Elevated intraocular pressure is a leading risk factor for primary open-angle glaucoma," said Robert N. Weinreb, M.D., chair and distinguished professor of ophthalmology, and director of the Hamilton Glaucoma Center at the University of California, San Diego. "The higher the intraocular pressure, the more likely the person is to develop glaucoma and the more likely it is to progress."

Medications that lower eye pressure are a mainstay of glaucoma treatment. In some cases, a doctor may recommend surgery to increase fluid drainage from the eye. Drugs, surgery, or both approaches together are often successful at slowing the course of open-angle glaucoma. The NEI-funded Ocular Hypertension Treatment Study also found that pressure-lowering eye drops could delay the onset of glaucoma in people with high eye pressure. But even with medication or surgery, open-angle glaucoma usually continues to attack the optic nerve and cause gradual vision loss.

Who’s at risk?

There are several risk factors for open-angle glaucoma. Among them is age. Open-angle glaucoma is rare among Americans under age 50, but affects nearly eight percent of Americans over 80.

Other risks come into play long before we grow old and even before we're born. Open-angle glaucoma is about five times more common among African Americans and Mexican Americans compared to whites. It also has an earlier, more rapid course in African Americans.

Another strong influence is family history. A person's risk of developing open-angle glaucoma is about 10 times higher if a parent or sibling has it, and the risk is higher if an identical twin has it.

Data from family and twin studies has prompted researchers to dig more deeply into the genetics of open-angle glaucoma. It turns out that sometimes open-angle glaucoma is passed from parent to child due to defects within a single gene. Eight such genes have been identified so far, and they tend to cause glaucoma with an early onset, before age 50.

Thanks to these discoveries, there are now genetic tests that can help people with early-onset glaucoma determine the risk that their children will inherit the disease.

"As a community, there's still a lot we don't know about glaucoma," said Janey Wiggs, M.D., Ph.D., associate director of the Ocular Genomics Institute at the Massachusetts Eye and Ear Infirmary, part of Harvard Medical School in Boston. "However, we've been able to achieve some success by pooling resources and ideas. I think we will see more rapid progress in the next few years."

Visit www.nei.nih.gov for more information.

Comments

thank you for that info it gives ider of the type of glaucoma. My Dr said i have glaucoma but didnot said what type of glaucoma it is.I am so worrid.
Posted on February 24, 2014
 

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