by Lawrence Wood, Ophthalmologist
There’s one thing that most people know about glaucoma: Eye doctors test for it by blowing an annoying puff of air directly into your eye.
Actually, that test is rarely used these days; it has been replaced by several less-invasive (and much more comfortable) diagnostic procedures.
But the point is, the “air puff” test is as much as many people know about this serious and progressive eye disease. Left untreated, glaucoma can lead to blindness.
Moreover, it usually develops without pain or other symptoms, so many people don’t know they have it until the damage has already occurred. In fact, some 3 million Americans have glaucoma, but experts estimate that as many as half of those are unaware of it. It is the second leading cause of blindness worldwide and the most common cause among African-Americans.
In a healthy eye, a clear fluid called aqueous humor flows through the inside of the eye to nourish the lens, iris and cornea. The fluid then drains out through tiny holes that surround the iris, known as the trabecular meshwork, and then returns to the bloodstream. When fluid flows freely through the eye, the pressure inside your eye (called intraocular pressure or IOP) is normal.
One of the main causes of glaucoma is the inability of this fluid to flow freely. When fluid cannot drain, the pressure increases. More fluid flows in than drains out, causing the IOP to increase. Rising eye pressure slowly destroys the delicate fibers in the optic nerve that sends visual information from the eye to the brain. If the pressure is not corrected, you may lose part or all of your sight.
There are several types of glaucoma. In the most common type, open-angle glaucoma, the aqueous fluid has access to the drainage area, at the angle where the iris and the cornea merge. The angle is open but the fluid cannot exit the eye properly, causing an increase in IOP.
Often, this happens painlessly without symptoms or warning signs, and vision is gradually lost. Peripheral or side vision is usually affected first, with vision loss increasing over time. If detected and treated in the early stages, open-angle glaucoma usually responds well to medication.
In closed-angle glaucoma, fluid cannot flow freely between the cornea and the iris because the angle is partially or completely blocked. When this happens, the iris pushes forward and blocks the drainage holes.
Pressure inside the eye increases suddenly, often resulting in severe pain and immediate loss of vision. Other symptoms may include headaches, nausea, seeing “rainbows” around lights, and very blurred vision.
In fact, the name glaucoma comes from the Greek word meaning “hue.” Early physicians were probably describing the symptoms and color changes that occur with closed-angle glaucoma.
Other causes of glaucoma include injury, inflammation of the eye, eye tumor or advanced diabetes.
Glaucoma can affect anyone, but your risk may be higher if you:
- Are age 60 or older
- Are African-American or Asian
- Are severely nearsighted
- Have elevated intraocular pressure
- Have a family history of glaucoma
- Have diabetes or high blood pressure
- Have experienced an eye injury
Fortunately, in many cases glaucoma can be detected long before you develop symptoms of vision loss. Because glaucoma often has no warning signs, it is important to have your eye pressure tested regularly. Everyone should be screened for glaucoma at least every two years; if you have an increased risk, you should be tested every year.
There are four common glaucoma tests; regular check-ups usually include tonometry and ophthalmoscopy.
Tonometry measures the inner pressure of the eye. Instead of the “air puff” test, the doctor will numb the eye with drops, then use a special device to measure IOP.
Ophthalmoscopy involves using a light and a lens to examine the inside of the eye and the shape and color of the optic nerve.
If either of these two tests indicates potential problems, the doctor may perform one or two additional tests:
Also called a visual field test, perimetry tests peripheral vision and the function of the optic nerve. Looking straight ahead, you will be asked to respond when you see a light presented to you by the visual field machine.
Gonioscopy checks if the angle where the iris meets the cornea is open or closed to help determine whether glaucoma is present and what type.
Treatment depends on the type and severity of glaucoma. If your IOP is elevated, your ophthalmologist may prescribe eye drops or pills to control the pressure.
If the condition does not respond to medication, laser treatment called trabeculoplasty may be recommended. The laser stretches the tissue to open clogged drainage holds and restore normal flow.
Finally, trabeculectomy is an outpatient surgical procedure in which the surgeon makes a new drain in your eye to allow fluid to flow freely. Surgery takes about an hour. After your eye heals, you may need medication to keep the pressure under control.
This Scripps Health and Wellness information was provided by Lawrence Wood, MD, an ophthalmologist at Scripps Memorial Hospital La Jolla.