Glaucoma is a collection of diseases that damages the eye’s optic nerve. If left untreated, it can cause blindness. Three million Americans suffer from glaucoma, and only one-half of those with the disease realize they have it.
Glaucoma generally develops without early symptoms and usually progresses slowly. It can steal your eyesight very gradually. Fortunately, early detection and treatment can help preserve your vision.
The most common form of glaucoma is called primary open angle glaucoma. It occurs when the trabecular meshwork (an area of tissue in the eye located around the base of the cornea responsible for draining the aqueous humor from the eye via the chamber on the front of the eye covered by the cornea) decreases outflow. As this occurs, your eye pressure, also referred to as the intraocular pressure or IOP, increases. Raised eye pressure leads to damage of the optic nerve. Damage to the optic nerve can occur at different eye pressures among different patients. Your eye doctor will establish a target eye pressure for you that will assist to protect your optic nerve from further damage. Each individual patient may have a specific target IOP.
Half of patients with glaucoma do not have high eye pressure when first examined. That is why it is important that the optic nerve be examined and evaluated by your eye doctor for accurate diagnosis and treatment.
Typically, open angle glaucoma has no symptoms in its early stages and your vision remains normal. As the optic nerve becomes more damaged, blind spots begin to appear in your field of vision. You typically will not notice these blind spots in your vision until the optic nerve is significantly and permanently damaged when these spots become large. If all of the optic nerve fibers die, blindness is the result.
A less common form of glaucoma is closed angle or narrow angle glaucoma.
Closed angle glaucoma occurs when the drainage angle of the eye becomes partially or completely blocked. Unlike open angle glaucoma, the eye pressure rises very quickly. The pressure increases 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 kind of glaucoma.
If the drainage angle becomes completely blocked, eye pressure rises quickly resulting in a closed angle glaucoma attack. Symptoms of a closed angle attack include:
- Severe eye or brow pain
- Redness of the eye
- Decreased or blurred vision
- Seeing colored rainbows or halos
A closed angle glaucoma attack is a medical emergency and must be treated immediately.
Although normal IOP is considered a measurement of 21mm Hg or lower (millimeters of mercury, the same unit of measurement used in a weather barometer), this can be misleading. For those who have low tension or normal tension glaucoma, their eye pressure or IOP is consistently below 21mm Hg, but optic nerve damage and visual field loss can still occur.
Regular eye examinations are your best defense against glaucoma and other sight threatening eye disease.
Some factors that can increase the risk for developing glaucoma are:
- Family history of glaucoma
- African or Hispanic ancestry
- Farsightedness or nearsightedness
- Elevated eye pressure
- Previous eye injury
- Thin corneas
- Disorders that cause abnormalities in blood flow, such as migraines, diabetes and low blood pressure.