Tests for glaucoma

Ophthalmologists use three types of tests to screen for glaucoma in people at risk. These tests also help monitor people during treatment. The three tests are tonometry to measure intraocular pressure, ophthalmoscopy to inspect the optic nerve, and perimetry to test the visual fields. A high IOP warrants further testing, and the final diagnosis is made by also finding evidence of optic nerve damage. The doctor could also diagnose you by identifying defects in the visual fields characteristic of glaucoma.

    * Tonometry measures intraocular pressure or IOP, by assessing the amount of force necessary to make a slight indentation in a small area of the cornea. The most effective way to do this is with applanation tonometry, where anesthetic eye-drops are going into numb the eye. Then, the doctor will apply slight pressure to the cornea using a small instrument while he looks through a table-mounted microscope. A handheld tonometry device is also sometimes used and is relatively accurate. Tonometry is painless and poses virtually no risk to the cornea during this test.

    * Ophthalmoscopy is a specific examination of the optic nerve, required for the diagnosis of glaucoma. It also helps with periodic examinations of the nerve valuable to follow the progress of the disorder during treatment. To perform ophthalmoscopy, the doctor dilates pupils with eye-drops and then uses an ophthalmoscope. This is a special instrument with a small light on one end to magnify and examine the optic nerve. Another type of ophthalmoscopy uses a specialized microscope that allows three-dimensional visualization of your optic nerve. Signs of a damaged optic nerve include cupping in its center and a loss of its normal pink color.

    * Perimetry is a procedure where the patient wears a patch over one eye and looks straight ahead at a bowl-shaped white area. At the same time, the computer presents lights in fixed locations around the bowl. The patient indicates each time he or she sees a light, which is why perimetry is able to provide a map of the visual fields. The type of vision loss associated with glaucoma is relatively specific, and perimetry can detect the typical visual-field defects of glaucoma disorder.

A thorough eye examination including gonioscopy with a Goldmann or Zeiss goniolens is a prerequisite prior to undergoing specific tests for glaucoma. In glaucoma management, serial tests over several years have more value than a single one-time test for diagnosis. Therefore, it is important that the same type of test is repeated many times over a period of several years. The reason for this is that we are trying to ascertain whether a given target pressure has indeed stopped further damage to the eye. This determination is only possible if we have examinations from previous years to compare against, and it can show that there are no new findings or worsening. Therefore, one must maintain good long-term records and if you change physicians for any reason, it is important that you have all prior records forwarded to the current physician.

The newer tests for glaucoma

The visual field test depends upon patient responses. The new tests are nerve fiber analyzers, and these adopt a different objective strategy that is not dependent on patient responses. These tests measure the physical thickness of the nerve fibers in the retina. Since in glaucoma the nerve fibers are lost, patients with glaucoma are likely to have thinner nerve fiber layers. By measuring changes in nerve fiber layer thickness over time, these tests can detect glaucoma progression. The validity of these tests has been established in many peer-reviewed reports. Perhaps these tests will become the gold standards in the future as more professionals gain experience with these types of tests; however at present they are considered supplemental tests in glaucoma diagnosis at best. Going by the logic that more information is better than less, a reasonable argument is easy to get from these tests in addition to the traditional tests, even if their role in glaucoma management is debatable.