Glaucoma is a condition that causes damage to the eye’s optic nerve. The optic nerve is connected to the retina which is a layer of light-sensitive tissue lining the back of the eye. The optic nerve is made up of many nerve fibers, like an electric cable is made up of many wires. It is the optic nerve that sends signals from your retina to your brain, where these signals are interpreted as the images you see.
In a healthy eye, a clear fluid called aqueous humor is located inside the anterior part of your eye. To maintain a constant healthy eye pressure, your eye produces and drains an equal amount of aqueous humor continuously. If you have glaucoma, the aqueous humor does not flow out of the eye properly. Fluid pressure in the eye slowly rises and, over time, causes damage to the optic nerve fibers.
Glaucoma can permanently damage your vision if it is left untreated. Only about half of the estimated three million Americans who have glaucoma are even aware that they have the condition. Fortunately, early detection and treatment can help preserve your vision.
There are several types of glaucoma:
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 rises. Raised eye pressure leads to damage of the optic nerve. Damage to the optic nerve can occur at different eye pressures among different patients. If your ophthalmologist (Eye M.D.) finds any damage to your optic nerve, he or she will lower your eye pressure to 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 the patient experiences normal vision. 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.
Half of patients with glaucoma do not have high eye pressure when first examined. Some such individuals will only occasionally have high eye pressures on repeat testing; thus, a single eye pressure test misses many with glaucoma. In addition to routine eye pressure testing, it is essential that the optic nerve be examined by an ophthalmologist for proper diagnosis.
Some people have a type of glaucoma called normal-tension, or low-tension glaucoma. Their eye pressure is consistently low when measured in the office but optic nerve damage and visual field loss still occur. Normal-tension glaucoma patients typically receive the same methods of treatment used for open-angle glaucoma.
Conversely, ocular hypertension is a condition where someone has higher eye pressure than normal, but does not have other signs of glaucoma, such as optic nerve damage or blank spots that show up in their peripheral (side) vision when tested. Individuals with ocular hypertension are at higher risk for developing glaucoma later. Like people with glaucoma, people with ocular hypertension should be monitored closely by an ophthalmologist to ensure they receive appropriate treatment.
A less common form of glaucoma is closed angle. Closed-angle glaucoma (or narrow angle glaucoma) occurs when the drainage canal of the eye becomes obstructed. Unlike open-angle glaucoma, eye pressure usually goes up quickly. The pressure rises because the iris — the colored part of the eye — partially or completely blocks off the drainage angle. People of Asian descent and those with hyperopia (farsightedness) tend to be more at risk for developing this form of glaucoma.
If the drainage angle becomes completely blocked, eye pressure rises quickly resulting in a closed-angle glaucoma attack. Symptoms of an attack include:
Severe eye or brow pain
Redness of the eye
Decreased or blurred vision
Seeing colored rainbows or halos
Secondary glaucoma is glaucoma that results from another eye condition or disease. Some examples of conditions causing secondary glaucoma include but not limited to, someone who has had an eye injury, someone who is on long-term steroid therapy or someone who has an intraocular tumor.