What is exactly glaucoma?

Glaucoma isn't a single disease. It is the name for a group of eye conditions in which the optic nerve is damaged at the point where it leaves the eye. The human eye needs a certain amount of pressure to keep the eyeball in shape so that it can work properly. In some people, the damage is caused by raised eye pressure. Others may have an eye pressure within normal limits but damage occurs because there is a weakness in the optic nerve. The biggest  problem with glaucoma is that damage to the optic nerve causes impaired vision, which sometimes may progress to blindness.

Incidence of the condition

Glaucoma is the second most common cause of blindness in the US. As of the year 2000, an estimated 2.47 million people in the United States had glaucoma and more than 130,000 were legally blind because of this disease. These statistics alone emphasize the need to identify and closely monitor people who are at risk of developing glaucoma, particularly those with ocular hypertension.

Studies estimate that 3-6 million people in the United States alone, including 4-10% of the population older than 40 years, have intraocular pressures of 21 mm Hg or higher, without detectable signs of glaucomatous damage.

Common types of glaucoma

There are four most common types of glaucoma and they are:

Open Angle Glaucoma
Open angle glaucoma is the most common type of glaucoma. In this type, even though the anterior structures of the eye appear normal, aqueous fluid builds up within the anterior chamber, causing the intraocular pressure to become elevated. The big problem with this type of glaucoma is that, if left untreated, it may cause permanent damage to the optic nerve and retina.  Patients with open angle glaucoma usually have no symptoms.

Acute Angle Closure
Only about 10% of the population with glaucoma has this type. Unlike the previous type, acute angle closure occurs because of an abnormality of the structures in the front of the eye. Actally, the space between the iris and cornea is a little more narrow than normal. This leaves a smaller channel for the aqueous to pass through. This type of glaucoma usually comes very slowly although, if the flow of aqueous becomes completely blocked, the intraocular pressure rises sharply, causing a sudden angle closure attack. Patients with angle closure glaucoma may experience severe eye pain accompanied by nausea, blurred vision, rainbows around lights, and a red eye.
 
Secondary Glaucoma
This type occurs as a result of another disease or problem within the eye such as:

• inflammation
• trauma
• previous surgery
• diabetes
• tumor
• certain medications

In cases of secondary glaucoma, both the glaucoma and the underlying problem must be treated.

Congenital Glaucoma
This is a rare type of glaucoma that is generally seen in infants.