Glaucoma is a disease that damages your eye’s optic nerve. It usually happens when fluid builds up in the front part of your eye. That extra fluid increases the pressure in your eye, damaging the optic nerve.
In a healthy eye, excess fluid leaves the eye through the drainage angle, keeping pressure stable.
The optic nerve is connected to the retina — a layer of light-sensitive tissue lining the inside of the eye — and is made up of many nerve fibers, like an electric cable is made up of many wires. The optic nerve sends signals from your retina to your brain, where these signals are interpreted as the images you see.
In the healthy eye, a clear fluid called aqueous (pronounced AY-kwee-us) humor circulates inside the front portion of your eye. To maintain a constant healthy eye pressure, your eye continually produces a small amount of aqueous humor while an equal amount of this fluid flows out of your eye. If you have glaucoma, the aqueous humor does not flow out of the eye properly. Fluid pressure in the eye builds up and, over time, causes damage to the optic nerve fibers.
The most common form of glaucoma is called primary open-angle glaucoma. It occurs when the trabecular meshwork of the eye gradually becomes less efficient at draining fluid. As this happens, your eye pressure, called intraocular pressure (IOP), rises. Raised eye pressure leads to damage of the optic nerve. Damage to the optic nerve can occur at different eye pressures in different patients. There is not one ‘right’ eye pressure that is the same for everyone. Your ophthalmologist (Eye M.D.) establishes a target eye pressure for you that he or she predicts will protect your optic nerve from further damage. Different patients have different target pressures.
Typically, open-angle glaucoma has no symptoms in its early stages and your vision remains normal. As the optic nerve becomes more damaged, blank spots begin to appear in your field of vision. You usually won’t notice these blank spots in your day-to-day activities until the optic nerve is significantly damaged and these spots become large. If all of the optic nerve fibers die, you will be blind.
Half of patients with glaucoma do not have high eye pressure when first examined. Eye pressure is not always the same – it rises and falls from day to day and hour to hour. So a single eye pressure test will miss many people who have glaucoma. In addition to routine eye pressure testing, it is essential that the optic nerve be examined by an ophthalmologist for proper diagnosis.
Eye pressure is expressed in millimeters of mercury (mmHg), the same unit of measurement used in weather barometers.
Although “normal” eye pressure is considered a measurement less than 21 mmHg, this can be misleading. Some people have a type of glaucoma called normal-tension, or low-tension glaucoma. Their eye pressure is consistently below 21 mmHg, but optic nerve damage and loss of vision still occur. People with normal-tension glaucoma are usually treated in the same way as people who have open-angle glaucoma.
This type happens when someone’s iris is very close to the drainage angle in their eye. The iris can end up blocking the drainage angle. You can think of it like a piece of paper sliding over a sink drain. When the drainage angle gets completely blocked, eye pressure rises very quickly. This is called an acute attack. It is a true eye emergency, and you should call your ophthalmologist right away or you might go blind. People of Asian descent and those with hyperopia (farsightedness) tend to be more at risk for developing this form of glaucoma.
Symptoms of an acute attack include:
A closed-angle glaucoma attack is a medical emergency and must be treated immediately. Unfortunately, people at risk for developing closed-angle glaucoma often have few or no symptoms before the attack.
People at risk for closed-angle glaucoma should avoid over-the-counter decongestants and other medications where the packaging states not to use these products if you have glaucoma. These products are usually safe to use once your narrow angle has been treated with laser iridotomy. Always ask your ophthalmologist if it is safe for you to use products with this warning.
Congenital glaucoma is a rare type of glaucoma that develops in infants and young children and can be inherited. While less common than the other types of glaucoma, this condition can be devastating, often resulting in blindness if not diagnosed and treated early.
Secondary glaucoma is glaucoma that results from another eye condition or disease. For example, someone who has had an eye injury, someone who is on long-term steroid therapy or someone who has a tumor may develop secondary glaucoma. The most common forms of secondary glaucoma are: pseudoexfoliative glaucoma, pigmentary glaucoma, and neovascular glaucoma.
Some people have normal eye pressure but their optic nerve or visual field looks suspicious for glaucoma. These people must be watched carefully because some eventually develop definite glaucoma and need treatment.
Other people have an eye pressure that is higher than normal, but they do not have other signs of glaucoma, such as optic nerve damage or blank spots that show up in their peripheral (side) vision when tested. This condition is called ocular hypertension. Individuals with ocular hypertension are at higher risk for developing glaucoma compared to people with lower, or average, eye pressure. Just like people with glaucoma, people with ocular hypertension need to be closely monitored by an ophthalmologist to ensure they receive appropriate treatment.