Eye disease - Glaucoma (3 of 3)

Eye disease - Glaucoma (3 of 3):

How is glaucoma diagnosed?

An eye doctor (ophthalmologist) can usually detect those individuals who are at risk for glaucoma (because of, for example, a narrow drainage angle or increased intraocular pressure) before nerve damage occurs. The doctor also can diagnose patients who already have glaucoma by observing their nerve damage or visual field loss. The following tests, all of which are painless, may be part of this evaluation.

• Tonometry determines the pressure in the eye by measuring the tone or firmness of its surface. Several types of tonometers are available for this test, the most common being the applanation tonometer. After the eye has been numbed with anestheticeyedrops, the tonometer's sensor is placed against the front surface of the eye. The firmer the tone of the surface of the eye, the higher the pressure reading.

• Pachymetry measures the thickness of the cornea. After the eye has been numbed with anesthetic eyedrops, the pachymeter tip is touched lightly to the front surface of the eye (cornea). Studies have shown that corneal thickness can affect the measurement of intraocular pressure. Thicker corneas may give falsely high eye pressure readings and thinner corneas may give falsely low pressure readings. Furthermore, thin corneas may be an additional risk factor for glaucoma. Once a doctor knows the thickness of a patient's cornea, he or she can more accurately interpret the patient'stonometry.

• Gonioscopy is done by numbing the eye with anesthetic drops and placing a special type of contact lens with mirrors inside the eye. The mirrors enable the doctor to view the interior of the eye from different directions. The purpose of this test is to examine the drainage angle and drainage area of the eye. In this procedure, the doctor can determine whether the angle is open or narrow and find any other abnormalities within the angle area. As indicated earlier, individuals with narrow angles have an increased risk for a sudden closure of the angle, which can cause an acute angle-closure glaucomatous attack. Gonioscopy can also determine whether the eye is subject to chronic angle closure, whether blood vessels are abnormal, or whether hidden tumors might be blocking the drainage of the aqueous fluid out of the eye.

• Ophthalmoscopy is an examination in which the doctor uses a handheld device to look directly through the pupil (the opening in the colored iris) into the eye. This procedure is done to examine the optic nerve (seen as the opticdisc) at the back of the eye. Damage to the optic nerve, called cupping of the disc, can be detected in this way. Cupping, which is an indentation of the optic disc, can be caused by increased intraocular pressure. Additionally, a pale color of the nerve can suggest damage to the nerve from poor blood flow or increased intraocular pressure. Special cameras can be used to take photographs of the optic nerve to compare changes over time.

• Visual field testing actually maps the visual fields to detect any early (or late) signs of glaucomatous damage to the optic nerve. In order to find and follow glaucoma, visual fields are measured by a computer one eye at a time. One eye is covered and the patient places his or her chin in a type of bowl. Lights of various intensity and size are randomly projected around inside of the bowl. When the patient sees a light, he or she pushes a button. This process produces a computerized map of the visual field, outlining the areas where the eye can or cannot see.

• Optic Nerve Tomography and NerveFiber Analysis create a three-dimensional image of the optic nerve to evaluate the nerve fiber layer and better evaluate optic nerve damage.

All of these tests are repeated at intervals of 1 to 4 times per year, depending on how well controlled the disease is, to assess the progression of the disease, and the effect of the treatment.

How often should someone be checked (screened) for glaucoma?

The following are the American Academy of Ophthalmology's recommended intervals for eye exams:

• Age 20-29: Individuals of African descent or with a family history of glaucoma should have an eye examination every three to five years. Others should have an eye exam at least once during this period.
• Age 30-39: Individuals of African descent or with a family history of glaucoma should have an eye examination every two to four years. Others should have an eye exam at least twice during this period.
• Age 40-64: Individuals should have an eye examination every two to four years.
• Age 65 or older: Individuals should have an eye examination every one to two years.

These routine screening eye examinations are mandatory since glaucoma usually causes no symptoms (asymptomatic) in its early stages. Once damage to the optic nerve has occurred, it cannot be reversed. Thus, in order to preserve vision, glaucoma must be diagnosed early and followed regularly. Patients with glaucoma need to be aware that it is a lifelong disease. Compliance with scheduled visits to the eye doctor and with prescribed medication regimens offers the best chance for maintaining vision.

What is the treatment for glaucoma?

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General approach

Although nerve damage and visual loss from glaucoma cannot usually be reversed, glaucoma is a disease that can generally be controlled. That is, treatment can make the intraocular pressure normal and, therefore, prevent or retard further nerve damage and visual loss. Treatment may involve the use of eyedrops, pills (rarely), laser ,or surgery.

In the United States, eyedrops are usually used first in treating most types of open-angle glaucoma. In contrast, in Europe, laser or surgery is sometimes the first choice of treatment. One or more types of eyedrops may have to be taken up to several times a day to lower intraocular pressure. These drops work either by reducing the production of the aqueous fluid (shutting the faucet) or by increasing the drainage of the fluid out of the eye. Each type of therapy has its benefits and potential complications.

Concluded