Glaucoma is the third most common cause of blindness in the US. There are four major types of glaucoma:
- Closed angle (acute) glaucoma
- Open angle (chronic) glaucoma
- Congenital glaucoma
- Secondary glaucoma
All four types of glaucoma are characterized by increased pressure within the eyeball, and therefore all can cause progressive damage to the optic nerve.
Increased pressure occurs when the fluid within the eye (called aqueous humor) does not drain properly. The pressure pushes on the junction of the optic nerve and the retina at the back of the eye. This reduces the blood supply to the optic nerve, which carries visual information from the eye to the brain.
This loss of blood supply causes the individual nerve cells to progressively die. As the optic nerve deteriorates, blind spots develop in the field of vision. Peripheral (side) vision is affected first, followed by or central (front) vision. Without treatment, glaucoma can eventually cause blindness.
Closed angle (acute) glaucoma may occur in people who were born with a narrow angle between the iris and the cornea (the anterior chamber angle). This is more common in people who are farsighted (they see objects in the distance better than those which are close up). The iris may slip forward and suddenly close off the exit of aqueous humor, and a sudden increase in pressure within the eye follows.
Symptoms of pain, redness, nausea, and visuon loss develop rapidly. Angle closure may be provoked in susceptible persons by the use of drops that dilate the eyes. Attacks may also develop without any obvious triggering event. This is more common in the evening because the eye's pupils naturally dilate in dim light.
Open angle (chronic) glaucoma is by far the most common type of glaucoma. In open angle glaucoma, the iris does not block the drainage angle as it does in acute glaucoma. Instead, the fluid outlet channels within the wall of the eye gradually narrow with time. The disease usually affects both eyes, and over a period of years the consistently elevated pressure slowly damages the optic nerve.
Chronic glaucoma has no early warning signs, and the associated loss of peripheral vision occurs so gradually that it may go unnoticed until a substantial amount of damage and vision loss have occurred. The only way to diagnose glaucoma early is through routine eye examinations.
Secondary glaucoma is caused by other diseases, including eye diseases such as uveitis, systemic diseases, and drugs such as corticosteroids.
Congenital glaucoma, which is present at birth, is the result of defective development of the fluid outflow channels of the eye. Surgery is required for correction. Congenital glaucoma is often hereditary.
Risk factors depend on the type of glaucoma. For chronic glaucoma, risk factors include the following:
People with a family history of open angle glaucoma have twice the risk of developing open angle glaucoma as those who do not. African-Americans have four times the risk of developing open angle glaucoma compared to Caucasian Americans. It is estimated that 1% to 2% of people over 40 have chronic glaucoma, with about 25% of cases undetected.
The risk factors for acute glaucoma include the following:
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Family history of acute glaucoma
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Farsightedness
- Use of systemic anticholinergic medications (such as atropine or eye dilation drops) in a high-risk individual
Acute, congenital, and secondary glaucoma are much less common than chronic glaucoma.
