Health A-Z

Medical Content Created by the Faculty of the
Harvard Medical School

Glaucoma

Diagnosis

In most cases, open angle glaucoma is diagnosed by a doctor during a routine eye examination. When looking at the back of the eye (fundus) using a special telescope, he or she may notice changes in the appearance of the optic nerve. If glaucoma is suspected, your doctor will confirm the diagnosis with one or more additional tests:

• Tonometry measures the pressure within the eye. This may be done by pressing an instrument against your eyeball, or by blowing a puff of air against your eye. Your eye pressure is measured in millimeters of mercury, commonly abbreviated as "mmHg." Normal eye pressure is between 8 mmHg and 22 mmHg.

• Visual-field testing is the best way to find early signs of loss of peripheral vision. Most often, visual fields are checked using an automated machine. You look straight ahead into the machine and press a button when you see a blinking light. The machine then draws a picture of where you are able to see the blinking lights.

• OCT. This technique uses a LASER beam to actually measure the thickness of the nerve fibers in the retina. Glaucoma causes loss of these nerve fibers.

Your doctor will not diagnose glaucoma unless your optic nerve shows evidence of damage. However, some people will be found to have elevated eye pressure but no evidence of optic nerve damage. In this case, you may be told that you are a "glaucoma suspect" or have "pre-glaucoma," but do not yet have the disease. It is important to remember that not everyone with elevated pressures will develop glaucoma, and that not everyone with glaucoma has elevated eye pressures.

Angle closure glaucoma usually is diagnosed in a person who has developed a red, swollen eye and difficulties with vision. The eye pressure is usually quite high. Some people may be told by their eye doctor that they are at risk of angle closure glaucoma because their angle looks narrow.