Glaucoma is an eye disease that can damage your optic nerve. The optic nerve supplies visual information to your brain from your eyes.
Glaucoma is usually, but not always, the result of abnormally high pressure inside your eye. Over time, the increased pressure can erode your optic nerve tissue, which may lead to vision loss or even blindness. If it’s caught early, you may be able to prevent additional vision loss.
Glaucoma is usually, but not always, associated with elevated pressure in the eye (intraocular pressure). Generally, it is this elevated eye pressure that leads to damage of the eye (optic) nerve. In some cases, glaucoma may occur in the presence of normal eye pressure. This form of glaucoma is believed to be caused by poor regulation of blood flow to the optic nerve.
Worldwide, glaucoma is the second leading cause of irreversible blindness. In fact, as many as 6 million individuals are blind in both eyes from this disease. In the United States alone, according to one estimate, more than 3 million people have glaucoma. As many as half of these individuals with glaucoma may not know that they have the disease. The reason they are unaware of the presence of the disease is that glaucoma initially causes no symptoms, and the subsequent loss of side vision (peripheral vision) is usually not recognized.
Elevated pressure in the eye is the main factor leading to glaucomatous damage to the eye (optic) nerve. Glaucoma with normal intraocular pressure is discussed below in the section on the different types of glaucoma. The optic nerve, which is located in back of the eye, is the main visual nerve for the eye. This nerve transmits the images we see back to the brain for interpretation. The eye is firm and round, like a basketball. Its tone and shape are maintained by a pressure within the eye (the intraocular pressure), which normally ranges between 8 millimeters (mm) and 22 mm of mercury. When the pressure is too low, the eye becomes softer, while an elevated pressure causes the eye to become harder. The optic nerve is the most susceptible part of the eye to high pressure because the delicate fibers in this nerve are easily damaged either by direct pressure on the nerve or decreased blood flow to the nerve.
The front of the eye is filled with a clear fluid called the aqueous humor, which provides nourishment to the structures in the front of the eye. This fluid is produced constantly by the ciliary body, which surrounds the lens of the eye. The aqueous humor then flows through the pupil and leaves the eye through tiny drainage channels called the trabecular meshwork. These channels are located at what is called the drainage angle of the eye. This angle is where the clear cornea, which covers the front of the eye, attaches to the base (root or periphery) of the iris, which is the colored part of the eye. The cornea covers the iris and the pupil, which are in front of the lens. The pupil is the small, round, black-appearing opening in the center of the iris. Light passes through the pupil, on through the lens, and to the retina at the back of the eye. Please see the figure, which is a diagram that shows the drainage angle of the eye.
⇔ Severe eye pain
⇔ Redness in your eye
⇔ Sudden vision disturbances
⇔ Seeing colored rings around lights
⇔ Sudden blurred vision
⇔ Open-Angle (Chronic) Glaucoma Open-angle, or chronic, glaucoma has no signs or symptoms except gradual vision loss. This loss may be so slow that your vision can suffer irreparable damage before any other signs become apparent. According the National Eye Institute (NEI), this is the most common type of glaucoma.
⇔ Angle-Closure (Acute) Glaucoma If the flow of your aqueous humor fluid is suddenly blocked, the rapid buildup of fluid may cause a severe, quick, and painful increase in pressure. Angle-closure glaucoma is an emergency situation. You should call your doctor immediately if you begin experiencing symptoms, such as severe pain, nausea, and blurred vision.
⇔ Congenital Glaucoma Children born with congenital glaucoma have a defect in the angle of their eye, which slows or prevents normal fluid drainage. Congenital glaucoma usually presents with symptoms, such as cloudy eyes, excessive tearing, or sensitivity to light. Congenital glaucoma can run in families.
⇔ Secondary Glaucoma Secondary glaucoma is often a side effect of injury or another eye condition, such as cataracts or eye tumors. Medicines, such as corticosteroids, may also cause this type of glaucoma. Rarely, eye surgery can cause secondary glaucoma.
⇔ Normal Tension Glaucoma In some cases, people without increased eye pressure develop damage to their optic nerve. The cause of this isn’t known. However, extreme sensitivity or a lack of blood flow to your optic nerve may be a factor in this type of glaucoma.