What is Glaucoma?

Glaucoma is not just one eye disease, but a group of eye conditions resulting in optic nerve damage, which causes loss of vision. Abnormally high pressure inside your eye (intraocular pressure) usually, but not always, causes this damage.

Glaucoma is the second leading cause of blindness. Sometimes called the silent thief of sight, glaucoma can damage your vision so gradually you may not notice any loss of vision until the disease

Early diagnosis and treatment can minimize or prevent optic nerve damage and limit glaucoma-related vision loss. It's important to get your eyes examined regularly, and make sure your eye doctor measures your intraocular pressure.

Symptoms

The most common types of glaucoma — primary open-angle glaucoma and acute angle-closure glaucoma — have completely different symptoms.

Primary open-angle glaucoma signs and symptoms include:

• Gradual loss of peripheral vision, usually in both eyes
• Tunnel vision in the advanced stages

Acute angle-closure glaucoma signs and symptoms include:

• Severe eye pain
• Nausea and vomiting (accompanying the severe eye pain)
• Sudden onset of visual disturbance, often in low light
• Blurred vision
• Halos around lights
• Reddening of the eye

Both open-angle and angle-closure glaucoma can be primary or secondary conditions. They're called primary when the cause is unknown and secondary when the condition can be traced to a known cause, such as eye injury, inflammation, tumor, advanced cataract or diabetes. In secondary glaucoma, the signs and symptoms can include those of the primary condition as well as typical glaucoma symptoms.

When to see a doctor
Don't wait for noticeable eye problems. Primary open-angle glaucoma gives few warning signs or symptoms until permanent damage has already occurred. Regular eye exams are the key to detecting glaucoma early enough for successful preventive treatment.

The American Academy of Ophthalmology recommends a comprehensive eye exam for all adults starting at age 40, and every three to five years after that if you don't have any glaucoma risk factors. After age 60, you should be screened every year. If you are African-American or have other risk factors for glaucoma, your doctor likely will recommend periodic eye exams starting between ages 20 and 39, and every one to two years after age 40.

In addition, be aware that a severe headache or pain in your eye or eyebrow, nausea, blurred vision, or rainbow halos around lights may be the symptoms of an acute angle-closure glaucoma attack. If you experience two or more of these symptoms together, seek immediate care at an emergency room or an eye doctor's (ophthalmologist's) office right away.

Causes

For reasons that doctors don't completely understand, increased pressure within the eye (intraocular pressure) is usually associated with the optic nerve damage that characterizes glaucoma. This pressure comes from a buildup of aqueous humor, a fluid naturally and continuously produced in the front of your eye.

Aqueous humor normally exits your eye through a drainage system at the angle where the iris and the cornea meet. When the drainage system doesn't work properly, the aqueous humor can't filter out of the eye at its normal rate, and pressure builds within your eye.

Primary open-angle glaucoma
In primary open-angle glaucoma, the drainage angle formed by the cornea and the iris remains open, but the microscopic drainage channels in the angle (called the trabecular meshwork) are partially blocked, causing the aqueous humor to drain out of the eye too slowly. This leads to fluid backup and a gradual increase of pressure within your eye. Damage to the optic nerve is painless and so slow that a large portion of your vision can be lost before you're even aware of a problem. The exact cause of primary open-angle glaucoma remains unknown.

Angle-closure glaucoma
Angle-closure glaucoma, also called closed-angle glaucoma, occurs when the iris bulges forward to narrow or block the drainage angle formed by the cornea and the iris. As a result, aqueous fluid can no longer reach the trabecular meshwork at the angle, so the eye pressure increases abruptly. Angle-closure glaucoma usually occurs suddenly (acute angle-closure glaucoma), but it can also occur gradually (chronic angle-closure glaucoma).

Many people who develop closed-angle glaucoma have an abnormally narrow drainage angle to begin with. This narrow angle may never cause any problems, so it may go undetected for life.

If you have a narrow drainage angle, sudden dilation of your pupils may trigger acute angle-closure glaucoma. Pupils become dilated in response to darkness, dim light, stress, excitement and certain medications. These medications include antihistamines, such as desloratadine (Clarinex) and cetirizine (Zyrtec); tricyclic antidepressants, such as doxepin and protriptyline (Vivactil); and eyedrops used to dilate your pupils for a thorough eye exam.

Low-tension glaucoma
Another form of the disease, poorly understood but not uncommon, is low-tension glaucoma. In this form, optic nerve damage occurs even though eye pressure stays within the normal range. Why this happens is unknown. Some experts believe that people with low-tension glaucoma may have an abnormally sensitive optic nerve or a reduced blood supply to the optic nerve caused by atherosclerosis — an accumulation of fatty deposits (plaques) in the arteries — or another condition limiting circulation. Under these circumstances, optic nerve damage can occur even with normal pressure.

Pigmentary glaucoma
Pigmentary glaucoma, a type of glaucoma that can develop in young to middle-aged adults, is associated with a dispersion of pigment granules within the eye. The pigment granules appear to arise from the back of the iris. When the granules accumulate on and in the trabecular meshwork, they can interfere with the outflow of aqueous and cause a rise in pressure. Physical activities, such as jogging, sometimes stir up the pigment granules, depositing them on the trabecular meshwork and causing intermittent pressure elevations. This type of glaucoma can usually be easily diagnosed by your ophthalmologist.