By National Eye Institute| Last Updated
Glaucoma is an eye disease that can damage the optic nerve and result in vision loss and blindness. It occurs when the inner pressure of the eye slowly rises. With regular eye exams and early treatment, you can often protect your eyes from glaucoma and vision loss.
How Does Glaucoma Develop?
At the front of the eye there is a space between the iris and the cornea called the anterior chamber. It is filled with a clear intraocular fluid that continuously flows in and out of the chamber and nourishes nearby tissues. The fluid leaves the chamber where the cornea and iris meet, called the angle. When the fluid reaches the angle, it flows through a spongy meshwork of drainage canals and leaves the eye.
In some people, the fluid does not circulate properly. As it builds up, pressure inside the eye increases, like an over-filled water balloon. Left untreated, this elevated eye pressure can damage the optic nerve and vision loss may result.
Not every person with increased eye pressure will develop glaucoma. Some people can tolerate higher eye pressure better than others. Regular, comprehensive dilated eye exams will help your eye care professional monitor your eye health and determine what level of pressure is normal for you.
Glaucoma Risk Factors
Anyone can develop glaucoma, but some people are at higher risk than others are. High-risk populations include:
- African American, Asian, and Hispanic individuals;
- Everyone over age 60; and
- People with a family history of glaucoma.
A complete eye exam can reveal additional risk factors, such as high eye pressure, thinness of the cornea and abnormal optic nerve anatomy, and ensure you get the treatment you need to protect your vision. In some people with certain combinations of these risk factors, medicated eye drops can reduce the risk of developing glaucoma by about half.
Types of Glaucoma
This is the most common form of glaucoma. Open-angle glaucoma develops when intraocular fluid drains too slowly from the anterior chamber. The inner eye pressure (also called intraocular pressure or IOP) rises because the correct amount of fluid can’t drain out of the eye. With open-angle glaucoma, the entrances to the drainage canals are clear, but there is a clog further inside the meshwork, similar to a deep pipe clog below the drain in a sink.
Vision loss can occur if open-angle glaucoma is not diagnosed and treated, but it develops so slowly that changes in sight do not become noticeable for many years. Most people have no symptoms and no early warning signs. Peripheral vision loss is typically the first indicator. Open-angle glaucoma usually responds well to medication, especially with early detection and treatment.
Low-Tension or Normal-Tension Glaucoma
Optic nerve damage and vision loss can occur in people with normal eye pressure, though it is not clear why this happens. Lowering eye pressure at least 30 percent with medicated eye drops slows the disease in some people. A comprehensive medical history is important in identifying other potential risk factors, such as low blood pressure, atherosclerosis, and steroid use, which can contribute to low-tension and normal-tension glaucoma. If no other risk factors are identified, the treatment options for low-tension glaucoma are the same as for open-angle glaucoma.
People with this type of glaucoma (also known as narrow angle glaucoma) have a sudden increase in eye pressure when the angle is blocked by part of the iris and traps fluid at the front of the eye. Symptoms include severe pain, headache, nausea, redness of the eye and blurred vision. If you have these symptoms, seek treatment immediately. If your doctor is unavailable, go to the emergency room. Without treatment to restore the flow of fluid, damage to the optic nerve and vision loss can occur in the affected eye(s) in as few as one or two days. Usually, prompt laser surgery and medication can clear the blockage and protect sight.
Secondary glaucoma can develop as complications of other medical conditions, such as eye surgery, advanced cataracts, eye injuries, certain eye tumors, or uveitis (eye inflammation). Pigmentary glaucoma is a form of secondary glaucoma that occurs when pigment from the iris flakes off and blocks the meshwork, slowing fluid drainage. Another severe form called neovascular glaucoma is linked to diabetes. Corticosteroid drugs used to treat eye inflammation and other diseases can also trigger glaucoma in some people. Treatments vary depending on the underlying cause and can include medicines, laser surgery or conventional surgery.
Without treatment, people with glaucoma will slowly lose their peripheral (side) vision, which manifests as tunnel vision. Over time, central vision may also decrease until no vision remains.
Studies have shown that early detection and treatment are crucial to controlling the disease. If you fall into one of the high-risk groups for glaucoma, make sure to have a dilated eye exam at least every two years by an eye care professional.
If you are being treated for glaucoma, be sure to take your medication as directed and see your ophthalmologist regularly.
Testing for Glaucoma
Medicare Part B covers a glaucoma test every 12 months for seniors at high risk for glaucoma. Medicare-defined high-risk groups include individuals with diabetes, African Americans age 50 and older, and Hispanic Americans age 65 and older. Regular glaucoma check-ups include two routine eye tests: tonometry and ophthalmoscopy.
The tonometry test measures the inner pressure of the eye. Usually drops are used to numb the eye, and then the doctor or technician will use a special device to measures the eye’s pressure.
Ophthalmoscopy is used to examine the inside of each eye, especially the optic nerve. In a darkened room, the doctor will use an ophthalmoscope (an instrument with a small light on the end) to look at the shape and color of your optic nerve.
If the pressure in the eye is not within the normal range, or if the optic nerve looks unusual, then one or two additional glaucoma tests called perimetry and gonioscopy will be conducted.
The perimetry test is also called a visual field test. During this test, you will look straight ahead into a device called a perimeter and then indicate when you observe flashing light. This helps draw a “map” of your vision and identify any blind spots.
Gonioscopy is a painless eye test that checks if the angle where the iris meets the cornea is open or closed. This test determines if open-angle or closed-angle glaucoma is present and the type of treatment required.
The National Eye Institute conducts and supports research that leads to sight-saving treatments and plays a key role in reducing visual impairment and blindness.