What Is Normal-Tension Glaucoma?
Glaucoma is a disease that damages the optic nerve, which connects your eye to your brain so you can see. The condition usually is due to too much pressure in the eye. But the “normal-tension” kind is different.
There’s a fluid that normally circulates around the front of your eye. With many kinds of glaucoma, that fluid doesn’t drain as well as it should. So it backs up, much like water in a clogged drain. As a result, pressure builds up inside your eye. Over time, it starts to harm the optic nerve.
But with normal-tension glaucoma, the optic nerve becomes damaged even though eye pressure stays within normal levels. Your doctor may call it “low-tension” or “normal-pressure” glaucoma.
What Causes It?
Doctors aren’t sure why some people get normal-tension glaucoma. It may be that your optic nerve is more sensitive or fragile, so even normal amounts of pressure can damage it. The doctor should also ask whether you have had periods of abnormally low blood pressure either from excessive reaction to blood pressure medicine or from having had severe blood loss. This type of glaucoma also could be caused, in part, by not enough blood getting to your optic nerve.
Poor blood flow can damage and eventually kill the cells that carry signals from your eye to your brain. A condition such as atherosclerosis, which is the buildup of fatty deposits in the arteries, can hamper how well your blood circulates.
You’re more likely to get this type of glaucoma if you
- Have a family history of the condition
- Are of Japanese descent
- Have ever had heart disease
What Are the Symptoms of Normal-Tension Glaucoma?
You might not notice any problem in the early stages. Glaucoma is sometimes called a “silent thief of sight.”
Your optic nerve is like an electric cable. It’s made up of more than a million tiny fibers, or “wires.” As the nerve fibers die, you’ll begin to get blind spots in your vision. But you may not notice them until most of your optic nerve fibers are dead.
Without treatment, the first sign of normal-tension glaucoma is often the loss of your peripheral, or side, vision. You might start to miss things out of the corner of your eye.
As the condition gets worse, your vision narrows. It’s as if you’re looking through a tunnel. If all the fibers in your optic nerve die, you become blind.
Normal-tension glaucoma tends to worsen slowly. It’s important to keep up with your regular eye exams with an ophthalmologist. That’s a medical doctor who specializes in eye care and surgery. The exams can help find the disease before you lose vision.
Diagnosis
Your ophthalmologist will review your medical history and do a complete eye and vision exam. This will include taking your eye pressure.
You’ll get drops in your eyes to widen (or dilate) your pupils. Then your doctor will use a special magnifying glass to check the color and shape of your optic nerve. She’ll also look for any damage or defects. The doctor will use different tests to measure the pressure inside your eye as well as the thickness of your cornea in the front of the eye.
The ophthalmologist will also do what’s called a visual field test to check for any losses in your peripheral vision that you may not notice yourself.
Some people with normal-tension glaucoma have symptoms of blood vessel problems such as migraine headaches, cold hands and feet, or low blood pressure.