Up to 40 percent of a person's vision can be lost without them even noticing. The culprit: Glaucoma, a group of eye diseases that gradually steals sight without warning. The vision loss is caused by damage to the optic nerve. Yet there are virtually no symptoms.

Vision loss begins with peripheral or side vision, so if you have glaucoma, you may not notice any changes in your sight until significant vision is lost.

The Glaucoma Research Foundation calls the disease "the sneak thief of sight" since there are no symptoms and once vision is lost, it's permanent. January is Glaucoma Awareness Month, dedicated to raising awareness about the sight-stealing disease and urging people to get tested.

"Glaucoma is a leading cause of blindness. Over 2.2 million Americans, and over 60 million people worldwide, have glaucoma. Experts estimate that half of them don't know they have it. Combined with our aging population, we can see an epidemic of blindness looming if we don't raise awareness about the importance of regular eye examinations to preserve vision," according to the Glaucoma Research Foundation.

Glaucoma develops slowly and sometimes without noticeable sight loss for many years. By the time a person is aware of vision loss, the disease is usually quite advanced. Without proper treatment, glaucoma can lead to blindness.

Who is at risk?

People who are at higher risk include:

  • People of African, Asian, and Hispanic descent
  • People over 60
  • Family members of those already diagnosed
  • Diabetics
  • People who are severely nearsighted

There is no cure for glaucoma yet. However, medication or surgery can slow or prevent further vision loss. The appropriate treatment depends upon the type of glaucoma a person has. Early detection is vital to stopping the progress of the disease.

Getting tested

The best way to protect your sight from glaucoma is to get a comprehensive eye examination. Then, if you have glaucoma, treatment can begin immediately.

According to the Glaucoma Research Foundation, the eye doctor should use these five tests, each of which check different factors in order to make an accurate glaucoma diagnosis:

  • Tonometry – examines inner eye pressure
  • Ophthalmoscopy – Also known as a dilated eye exam, this test checks the shape and color of the optic nerve
  • Perimetry – This visual field test checks the complete field of vision
  • Gonioscopy – Examines the angle in the eye where the iris meets the cornea
  • Pachymetry – Test the thickness of the cornea

For more information, visit the Glaucoma Research Foundation website (www.glaucoma.org).