Glaucoma is a serious eye condition that can lead to vision loss and can even cause blindness. In many cases, glaucoma causes no symptoms in its early stages, so people do not realize they have a vision problem. Fortunately, early detection and treatment can slow the progression of vision loss.
Light carries visual information about nearby objects. This light enters the cornea, which is the transparent front part of the eye, and goes into the eye through the pupil. Once inside, the light strikes the light-sensitive tissue lining the back of the eye. This tissue, known as the retina, converts the visual information carried on the light into electrical impulses. The optic nerve transports these electrical signals from the retina to the brain, which then translates the impulses into the images we “see.”
Clear fluid fills the front part of the eye. This fluid, known as intraocular fluid or aqueous humor, provides nutrients to the eye and keeps the eye at the proper pressure. Excess fluid drains out through drainage canals in the pupils; the bloodstream absorbs the fluid.
Problems with the drainage canals can allow fluid to build up inside the eye, and this high fluid pressure can damage the optic nerve.
Prevalence of Glaucoma
The vision-robbing condition is very common, affecting about 3 million people in the United States, according to the Centers for Disease Control and Prevention (CDC). It is the leading cause of blindness in people aged 60 and older, according to the American Academy of Ophthalmology (AAO); the CDC says that glaucoma is the second leading cause of blindness worldwide.
The American Optometric Association recommends that people at risk for glaucoma undergo a dilated eye exam every year. A dilated eye exam is a pain-free test in which the eye doctor puts drops into the eye to dilate, or widen, the pupil. Dilating the pupil in this way allows the eye doctor to look inside the eye for signs of damage. Glaucoma tests are pain-free, although some glaucoma tests require numbing drops to make the patient more comfortable and to produce better results.
Five Common Tests
Early detection through regular, complete eye exams is the key to protecting the eyes from the damage glaucoma causes. A complete eye exam consists of five common tests that can detect signs of glaucoma. These five tests include:
- Tonometry – uses a small puff of air to measure the pressure inside the eye
- Ophthalmoscopy – helps the eye doctor examine the optic nerve for signs of damage from glaucoma; requires dilation of the pupil and the use of a small device with a light on its end that lights up and magnifies the optic nerve
- Perimetry – creates a map of the patient’s field of vision to determine if glaucoma has affected vision; the patient looks straight ahead as spots appear in their peripheral vision
- Gonioscopy – helps the eye doctor determine whether the angle where the patient’s iris meets the cornea is open and wide, or if it is narrow and closed; this test involves the use of numbing drops and the use of a handheld contact lens that shows the angle between the iris and the cornea
- Pachymetry – measures the thickness of the patient’s cornea, as thickness of the cornea can influence the pressure inside the eye; in this test, the eye doctor places a probe at the front of the eye to measure the cornea’s thickness
Researchers have not determined the exact cause of glaucoma. The condition may develop because the eye’s drainage system can become inefficient over time. Inadequate blood supply to the optic nerve may also play a role in the development of glaucoma.
There are two main forms of glaucoma: primary open-angle and acute-angle. There are other types such as secondary glaucoma which develops as the result of another illness, for example. Normal-tension glaucoma is a condition in which people have optic nerves that are overly sensitive to normal eye pressure.
Primary open-angle glaucoma
Primary open-angle glaucoma is the most common type. It typically begins slowly and without any symptoms, so people don’t realize they have the condition until they have already suffered vision loss.
This type happens when the eye does not drain well, somewhat like the clogged drain of a sink. Poor drainage causes the pressure inside the eye to rise; this excess pressure damages the optic nerve.
The condition starts very slowly and usually begins by affecting side vision, also known as peripheral vision. Vision loss can spread to central vision needed for reading and other close-up work. Left untreated, it can lead to significant loss in both eyes. Untreated glaucoma may also lead to blindness.
Acute angle-closure glaucoma
Acute angle-closure glaucoma, also known as narrow-angle or closed-angle, is less common. While glaucoma can be a chronic condition that develops slowly, it usually occurs suddenly after an abrupt rise in pressure inside the eye. Acute angle-closure is an emergency condition that requires immediate care from an optometrist.
This type usually happens when someone’s iris, which is the colored part of the eye, sits very close to the drainage angle. The iris can block the drainage angle, somewhat like a flat piece of paper sliding over the drain of a sink. When the drain is completely blocked, the pressure inside the eye rises very quickly. Eye care professionals refer to this as an “acute attack,” as it is a true eye emergency that may lead to blindness. While an acute attack often affects only one eye, the other eye is at increased risk of an attack as well.
Signs and Symptoms
Symptoms of acute angle-closure glaucoma can include:
- Severe eye pain
- Redness in the eye
- Blurred vision
- Seeing colored rings or halos around lights
- Halo effect around light sources
Certain factors increase the risk, including:
- Being over the age of 40
- Having family members with the condition
- Having African, Hispanic, or Asian heritage
- High eye pressure
- Being farsighted or nearsighted
- A history of eye injury
- The use of long-term steroid medications
- Corneas that are thin in the center
- Thinning of the optic nerve
- Diabetes, high blood pressure (hypertension), migraine headaches, poor blood circulation or other health problems affecting the whole body
There is currently no cure for glaucoma, which means vision lost to glaucoma cannot be restored. Early detection and prompt treatment can help preserve vision, however, and prevent further vision loss.
Medication or surgery can prevent or slow the progression of vision loss. There are a number of eye drop medications for glaucoma, including alpha agonists, beta-blockers and carbonic anhydrase inhibitors that reduce the amount of fluid produced by the eye. Miotic eye drops make the pupil smaller, which lowers eye pressure by increasing the amount of fluid that drains from the eye.
Laser surgery helps drain excess fluid from the eyes. Eye surgeons perform trabeculoplasty to help patients with open-angle glaucoma and iridotomy to help those with angle-closure glaucoma.