What is Glaucoma?

Post date: Oct 15, 2009 6:51:36 AM

Glaucoma refers to a group of related eye disorders that all cause damage to the optic nerve that carries information from the eye to the brain. Glaucoma usually has few or no initial symptoms.

In most cases, glaucoma is associated with higher-than-normal pressure inside the eye — a condition called ocular hypertension. But it also can occur when intraocular pressure (IOP) is normal. If untreated or uncontrolled, glaucoma first causes peripheral vision loss and eventually can lead to blindness. And because most cases of glaucoma have few or no early symptoms, about half of Australians with glaucoma don't know they have it.

Glaucoma is the second-leading cause of blindness in (behind macular degeneration), and the second-leading cause of blindness worldwide (behind cataracts).

Types Of Glaucoma

The two major categories of glaucoma are open-angle glaucoma (OAG) and narrow-angle glaucoma. The "angle" in both cases refers to the drainage angle inside the eye that controls the outflow of the watery fluid (aqueous) that is continually being produced inside the eye.

If the aqueous can access the drainage angle, the glaucoma is known as open angle glaucoma. If the drainage angle is blocked and the aqueous cannot reach it, the glaucoma is known as narrow-angle glaucoma.

Variations of OAG include: primary open angle glaucoma (POAG), normal-tension glaucoma (NTG), pigmentary glaucoma, pseudoexfoliation glaucoma, secondary glaucoma and congenital glaucoma.

Variations of narrow angle glaucoma include include acute angle closure glaucoma, chronic angle closure glaucoma, and neovascular glaucoma.

Glaucoma Symptoms

Glaucoma often is called the "silent thief of sight," because most types typically cause no pain and produce no symptoms until noticeable vision loss occurs.

For this reason, glaucoma often progresses undetected until the optic nerve already has been irreversibly damaged, with varying degrees of permanent vision loss.

But with acute angle-closure glaucoma, symptoms that suddenly occur can include blurry vision, halos around lights, intense eye pain, nausea and vomiting. If you have these symptoms, make sure you see an eye care practitioner or visit the emergency room immediately so steps can be taken to prevent permanent vision loss.

Diagnosis, Screening And Tests For Glaucoma

During our routine eye exams, a non-contact tonometer is used to measure your intraocular pressure or IOP.

An abnormally high IOP reading indicates a problem with the amount of fluid (aqueous humour) in the eye. Either the eye is producing too much fluid, or it's not draining properly.

Visual field testing is a way for your optometrist to determine if you are experiencing vision loss from glaucoma. Visual field testing involves staring straight ahead into a machine and clicking a button when you notice a blinking light in your peripheral vision. The visual field test may be repeated at regular intervals to make sure you are not developing blind spots from damage to the optic nerve or to determine the extent or progression of vision loss from glaucoma.

Gonioscopy also may be performed to make sure the aqueous humour (or "aqueous") can drain freely from the eye. In gonioscopy, special lenses are used with a slit-lamp to enable your optometrist to see the structure inside the eye (called the drainage angle) that controls the outflow of aqueous and thereby affects intraocular pressure.

Glaucoma Treatments

Treatment can involve glaucoma surgery, lasers or medication, depending on the severity. Eye drops with medication aimed at lowering IOP usually are tried first to control glaucoma.

Because glaucoma often is painless, people may become careless about the strict use of eye drops that can control eye pressure and help prevent permanent eye damage.

In fact, non-compliance with a program of prescribed glaucoma medication is a major reason for blindness caused by glaucoma.

If you find that the eye drops you are using for glaucoma are uncomfortable or inconvenient, never discontinue them without first consulting your optometrist about a possible alternative therapy.