|Glaucoma occurs when pressure inside the eyes builds because fluid to nourish eye tissue drains from the eyeball too slowly or suddenly stops draining.
Glaucoma (glaw-KOH-ma) is a group of diseases that cause vision loss or blindness by damaging the
optic nerve responsible for transmitting impulses for sight from the retina to the brain. In most cases, this damage results from increased pressure in the eye that occurs when fluid that flows in and out of the anterior chamber to bathe and nourish nearby tissue drains out too slowly or suddenly stops draining.
aqueous humor fluid circulates from behind your
iris through the
pupil, the dark opening in the center of your eye and into the space between your iris and your
cornea. Besides providing nourishment, the aqueous humor also exerts a constant pressure to help maintain your eyes' shape. To keep from building up in the eye, the fluid drains primarily through a "drainage angle," a mesh of tissue where the cornea and iris meet. In a healthy eye, the excess fluid then flows into a channel and into small veins on the outside of your eye.
But when the drainage angle doesn’t function properly, the aqueous humor backs up to apply pressure on another fluid, the
vitreous humor located behind the lens. This causes pressure inside the eyeball to increase. Unless controlled with medication or surgery, this can damage nerve fibers and other parts of the eye, causing a gradual loss in vision.
Glaucoma is the second leading cause of blindness in the U.S., and affects nearly 3 million Americans, most of whom are older than age 60. About 25 percent of people with glaucoma are considered legally blind; another 1 million others may be unaware they have this condition because the onset is so gradual. Glaucoma tends to run in families and is five times more common in African-Americans than Caucasians until middle age, when the risk tends to increase with age for all ethnic backgrounds.
There are two primary types of glaucoma:
- Open-angle glaucoma is the most common form, accounting for 60 to 70 percent of cases. It develops slowly and painlessly when there is too much aqueous humor or it doesn't drain properly. "Open-angle" refers to the "drainage angle." In primary open-angle glaucoma, there is too much aqueous being produced or it is not draining properly; in secondary open-angle glaucoma, other factors such as an anatomical variation to the eye, diabetes or medications can cause the pressure to increase in the same painless, progressive manner.
- Angle-closure glaucoma occurs in about 10 percent of cases. It is caused by a partial blockage of the angle and typically causes a sudden and dramatic increase in eye pressure that requires immediate medical attention. It is usually accompanied by some blurred vision, pain in or around the eye, redness, halos around lights and nausea and can result from using medications such as cold remedies, antidepressants and anti-nausea drugs.
There are also several rarer forms of the disease or syndromes that can lead to glaucoma:
- Congenital glaucoma, which typically affects children, is believed to result from an inherited developmental abnormality that blocks the eye drain. It typically occurs in infancy, childhood or adolesence.
- Secondary glaucoma, which usually results from trauma, chronic steroid use or disease.
- Normal-tension glaucoma occurs in people with normal intraocular pressure (IOP) that is below 22 mm Hg, but still develop optic nerve damage. (Meanwhile, others have high IOP but no optic nerve damage.)
- Pseudoexfoliation glaucoma occurs when both pigment and grayish material in the eye clog the angle meshwork.
- Pigment dispersion syndrome is a genetic disorder that causes glaucoma in up to 10 percent of people with this gene – usually people who are nearsighted.
Glaucoma often produces no initial symptoms. Vision is normal and there may be no pain. But as the disease progresses, you may first notice your peripheral vision gradually fading – especially near your nose. As the disease worsens, the field of vision narrows.
In open-angle glaucoma, you may develop "tunnel vision" -- vision has narrowed so you see only what is directly in front of you, like looking through a tunnel. This type tends to affect both eyes, although you may have symptoms in just one eye first. Besides reduced peripheral vision, you may notice:
- Sensitivity to glare
- Trouble differentiating between varying shades of light and dark
In closed-angle glaucoma, you may have a sudden onset of:
- Blurred vision
- Halos around lights at night
- Eye redness or pain
- Extreme weakness
- Nausea and vomiting
Glaucoma cannot be prevented, but the earlier it is diagnosed, the greater the likelihood that it can be slowed down or even stopped with medication before vision is significantly impacted. Once detected, eye pressure can be controlled to reach acceptable lower levels and nerve damage may slow or stop, although the damage is not reversed.
Many people are aware of the "air puff" test or other tests used to measure eye pressure in an eye examination; glaucoma is also found during an eye examination through dilated pupils, in which your eyecare provider adminsters eye drops to enlarge the pupils to see more of the inside of the eye. Because the gradual vision loss may not be noticed until it is too late, regular eye examinations are important for everyone older than age 40, particularly if you:
- Have a family history of glaucoma, which increases risk about four-fold
- Are African-American
- Have diabetes or hypertension (high blood pressure)
- Take corticosteroids and other medications that increase the pressure in your eye
- Have experienced trauma to the eye, such as an eye injury.
Medication is usually the first line of defense. Prescription eyedrops or pills help lower pressure inside the eyes by either slowing the flow of fluid into the eye or by improving drainage. Regular use of medication usually helps control increased pressure, but these drugs may not be as effective over time.
Surgery can also help fluid escape from the eye and thereby reduce the pressure, and is usually employed if medications are not helpful.
- Laser trabeculoplasty is the preferred treatment for open-angle glaucomas. In this procedure, a laser is used to widen the opening in the eye's drainage network. Eyedrops are often following this surgery.
- Laser iridotomy is used to treat angle-closure glaucoma. In this procedure, a laser makes a hole in the iris to allow the aqueous flow.
If medication and laser surgery are not successful, conventional eye surgery may be necessary to create a new opening for fluid to leave the eye. Although done on an out-patient basis, it takes longer than laser surgeries and is consdiered to be riskier.