Glaucoma (cont.)
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 filtering 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 anesthetic eye drops, 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 is a relatively new test being used for the management of glaucoma. Pachymetry determines the thickness of the cornea. After the eye has been numbed with anesthetic eye drops, the pachymeter tip is touched lightly to the front surface of the eye (cornea). Recent studies have shown that central 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.
- Gonioscopy is done by numbing the eye with anesthetic drops and placing a
special type of thick contact lens with mirrors inside on 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 filtering angle and drainage area of the
eye. In this procedure, the doctor can determine whether the angle is open or
narrow. As indicated earlier, individuals with narrow angles have an increased
risk for a sudden closure of the angle, which can cause an acute glaucomatous
attack. Gonioscopy can also determine if anything, such as abnormal blood
vessels, 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 optic disc) 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. This test can be done by having the patient look straight ahead and count the fingers shown by the examiner from the side. More typically, however, visual fields are measured by a computerized assessment. For this procedure, one eye is covered and the patient places his or her chin in a type of bowl. Then, when the patient sees lights of various intensities and at different locations, he or she pushes a button. This process produces a computerized map of the visual field.
Other, more sophisticated tests may also be employed. All of these tests need to be repeated at intervals to assess the progress of the disease and the effect of the treatment.
Next: How often should someone be checked (screened) for glaucoma? »
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