Open Angle Glaucoma
What is open-angle glaucoma?
Primary open-angle glaucoma, or POAG, is the most common of a group of eye disorders collectively known as glaucoma. All of these disorders result from damage to the optic nerve, or a bundle of nerves that send signals to the brain. POAG is sometimes known as a “silent thief” of sight, as symptoms often are not noticed until the optic nerve has already suffered irreversible damage. POAG affects an estimated 2.7 million people in the U.S. -- or about 2 percent of the population over age 40 -- and more than 60 million people across the globe. According to the World Health Organization, glaucoma is the second leading cause of blindness worldwide. It is also the leading cause of blindness in African-Americans.
What causes open-angle glaucoma?
Eyes naturally produce a fluid called aqueous humor. This fluid fills the space between the eye's iris, which gives the eye color and controls the pupil; and the cornea, the clear dome that covers and protects the iris. In addition to hydrating and nourishing the eyes with important vitamins for eyesight, the aqueous humor creates a pressure that gives the eye its shape, keeping it "inflated." Aqueous humor is constantly being produced, and must be naturally drained on an ongoing basis to maintain balance. In healthy eyes, this fluid drains through a system of spongy tissues known as trabecular meshwork that are located at the junction of the cornea and the iris. When the meshwork is unable to drain, due to a malfunction or congenital defect, aqueous humor builds up in the eye and creates what is known as high intraocular pressure (IOP).
Over time, high IOP causes damage to the optic nerve, which consists of a bundle of nerve fibers with a depression, or "cup," at its center. Primary open-angle glaucoma gradually enlarges the edge of this cup until it loses its rim, pinching off nerve endings and reducing the field of vision. If left untreated, the process eventually leads to significantly reduced vision or even blindness.
What are the symptoms of open-angle glaucoma?
Common open-angle glaucoma symptoms include a gradual loss of side or peripheral vision, difficulty adjusting to changes in light levels, and difficulty seeing in bright light or glare. When about 40 percent of nerves are lost, many POAG patients experience tunnel vision, or an inability to see any peripheral images. Symptoms may arise in both eyes or in a single eye. Because symptoms don’t usually appear until the disease has progressed, it is essential have a dilated eye exam at least every other year.
How is POAG detected and diagnosed?
Fortunately, this type of glaucoma is easy to diagnose. Ophthalmologists test for glaucoma at vision centers by performing tonometry, an air-puff test that measures intraocular pressure. They may also perform gonioscopy to examine eye drainage, perimetry to test peripheral vision, pachymetry to measure corneal thickness, and ophthalmoscopy to test optic nerve function.
Who is at risk for POAG?
While anyone can develop glaucoma, certain groups are more at risk. These include individuals with African or Latino ancestry; a family history of glaucoma, diabetes or anemia; people over age 50; and individuals with cardiovascular disease or hypertension. Other risk factors include nearsightedness, a history of steroid or corticosteroid use, and past injuries to the eye.
How is open-angle glaucoma treated?
Unfortunately, optic nerve damage is irreversible, and once vision is lost, it cannot be restored. However, POAG can be slowed or prevented through several treatment methods, including medication and surgery. Medication is the most common treatment and may work to slow the eye’s production of fluid or to enhance the eye’s ability to discharge fluid – both with the goal of reducing intraocular pressure.
Laser surgery decreases pressure by reducing fluid production or helping the eyes to drain more easily. Traditional surgery may be used to bypass the parts of the trabecular meshwork that are blocked, or even to create new drainage outlets. With treatment, most patients are able to control and slow the progression of the disease. Without treatment, however, optic nerve damage and loss of vision is almost inevitable.
Can POAG be prevented?
While some of the risk factors for this type of glaucoma are believed to be genetic – and therefore out of patients’ control – regular screenings and eye exams are key to identifying and treating the problem before it causes permanent damage. In addition, studies indicate that engaging in moderate aerobic exercise at least three times a week can lower intraocular pressure. Studies also suggest that carotenoids such as lutein, and antioxidants like vitamin C and zeaxanthin, may offer some benefits to POAG patients.