Glaucoma (cont.)
What are the risk factors for glaucoma?
Glaucoma is often called "the sneak thief of sight." This is because, as already mentioned, in most cases, the intraocular pressure can build up and destroy sight without causing obvious symptoms. Thus, awareness and early detection of glaucoma are extremely important because this disease can be successfully treated when diagnosed early. While everyone is at risk for glaucoma, certain people are at a much higher risk and need to be checked more frequently by their eye doctor. The major risk factors include:
- Age over 45 years
- Family history of glaucoma
- Black racial ancestry
- Diabetes
- History of elevated intraocular pressure
- Nearsightedness (high degree of
myopia), which is the inability to see distant objects clearly
- History of injury to the eye
- Use of cortisone
(steroids), either in the eye or systemically (orally or injected)
- Farsightedness (hyperopia), which
is seeing distant objects better than close ones (Farsighted people may have
narrow filtering angles, which predispose them to acute (sudden) attacks of closed-angle glaucoma.)
What are the different types of glaucoma?
There are many different types of glaucoma. Most, however, can be classified as either open-angle glaucomas, which are conditions of long duration (chronic), or closed-angle (angle closure) glaucomas, which include conditions occurring suddenly (acute). The glaucomas usually affect both eyes, but the disease can progress more rapidly in one eye than in the other. Involvement of just one eye occurs only when the glaucoma is brought on by factors such as a prior injury, inflammation, or the use of steroids in that eye.
Open-angle glaucoma
Chronic open-angle glaucoma (COAG) is by far the most common type of glaucoma. Moreover, its frequency increases greatly with age. This increase occurs because the drainage mechanism gradually may become clogged with aging. As a consequence, the aqueous fluid does not drain from the eye properly. The pressure within the eye, therefore, builds up painlessly and without symptoms. Furthermore, as mentioned previously, since the resulting loss of vision starts on the side (peripherally), people are usually not aware of the problem until the loss encroaches on their central visual area.
Normal tension (pressure) glaucoma is a variant of open-angle glaucoma that is being recognized more frequently than in the past. It is thought to be due to decreased blood flow to the optic nerve. This condition is characterized by progressive optic nerve damage and loss of peripheral vision (visual field) despite intraocular pressures in the normal range or even below normal. This type of glaucoma can be diagnosed by repeated examinations by the eye doctor to detect the nerve damage or the visual field loss. Currently, normal pressure glaucoma is receiving a lot of research attention because its cause and treatment are uncertain.
Congenital (infantile) glaucoma is a relatively rare, inherited type of open-angle glaucoma. In this condition, the drainage area is not properly developed. This results in increased pressure in the eye that can lead to the loss of vision from optic nerve damage and to an enlarged eye. The eye of a young child enlarges in response to increased intraocular pressure because it is more pliable than the eye of an adult. Early diagnosis and treatment with medicine and/or surgery are critical in these infants and children to preserve their sight.
Secondary glaucoma is another type of open-angle glaucoma. It can result from an eye (ocular) injury, even one that occurred many years ago. Other causes of secondary glaucoma are inflammation in the iris of the eye (iritis), diabetes, cataracts, or in steroid-susceptible individuals, the use of topical (drops) or systemic (oral or injected) steroids (cortisone). It can also be associated with a retinal detachment or retinal vein occlusion or blockage. (The retina is the layer that lines the inside of the back of the eye.) The treatments for the secondary glaucomas vary, depending on the cause.
Pigmentary glaucoma is a type of secondary glaucoma that is more common in younger men. In this condition, for reasons not yet understood, granules of pigment detach from the iris, which is the colored part of the eye. These granules then may block the trabecular meshwork, which, as noted above, is the drainage system of the eye. Finally, the blocked drainage system leads to elevated intraocular pressure, which results in damage to the optic nerve.
Exfoliative glaucoma (pseudoexfoliation) is another type of glaucoma that can occur with either open or closed angles. This type of glaucoma is characterized by deposits of flaky material on the front surface of the lens (anterior capsule) and in the angle of the eye. The accumulation of this material in the angle is believed to block the drainage system of the eye and raise the eye pressure. While this type of glaucoma can occur in any population, it is most prevalent in older people and people of Scandinavian descent.
Closed-angle glaucoma
Closed-angle glaucoma is a relatively rare type of glaucoma. In this condition, the patient's intraocular pressure, which ordinarily is normal, can go up very suddenly (acutely). This sudden pressure increase occurs because the filtering angle becomes closed and blocks off the drainage channels. This type of glaucoma can occur when the pupil dilates (widens or enlarges). As a result, the peripheral edge of the iris can become bunched up against its corneal attachment, thereby causing the filtering angle to close. Thus, the problem in closed-angle glaucoma is the difficulty with access of the eye fluid to the drainage system (trabecular meshwork). In contrast, remember that the problem in open-angle glaucoma is clogging within the drainage system itself.
People with small eyes are predisposed to developing closed-angle glaucoma because they tend to have narrow filtering angles. Small eyes are not obvious from their appearance, but they can be measured by an eye doctor. Thus, individuals who are farsighted or of Asian descent may have small eyes, narrow filtering angles, and an increased risk of developing closed-angle glaucoma. Furthermore, this condition may be triggered by medications that can dilate the pupils. These agents can be found in certain eye drops, cold remedies, or patches used to prevent seasickness. This condition can also occur spontaneously in a darkened room or a movie theater, wherein the pupil automatically dilates to let in more light. Sometimes, therefore, people with narrow angles are given eye drops to keep their pupils small. (See the section below on parasympathomimetic agents.)
A sudden glaucoma attack may be associated with severe eye pain and headache, a red (inflamed) eye, nausea, vomiting, and blurry vision. In addition, the high intraocular pressure leads to corneal swelling (edema), which causes the patient to see haloes around lights. Sometimes, acute glaucoma is treated with oral carbonic anhydrase inhibitors. (See the section below on these medications.) An attack of acute glaucoma, however, is usually relieved by eye surgery. In this operation, the doctor makes a small hole in the iris with a laser (laser iridotomy) to allow the fluid to resume draining into its normal outflow channels.
Next: How is glaucoma diagnosed? »
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