Medical Health Encyclopedia

Other Devices. Computer-assisted devices, such as the confocal scanning laser ophthalmoscope, are now available that may be useful for evaluating the retinal nerve layer. Another instrument, the optical coherence tomograph, measures the echo time delay of light that is scattered back from different layers in the retina. The value of these tests has not yet been determined.

Perimetry and Other Tests of the Visual Fields

If there is indication of optic nerve damage, the eye professional will conduct tests of the visual fields (the areas that the patient can see). In most people with glaucoma, the first areas to become noticeably impaired are the peripheral visual fields (areas of sight that are not directly in front of a person but more to the sides).

Click the icon to see an image of the visual field test.

Standard Perimetry Tests. Perimetry tests are used to check peripheral vision. One variation of this test is as follows:

• A person sits closely facing a large computer-like monitor.
• Small bright white lights flicker on and off hundreds of times, at different places on the screen, while the patient clicks a button whenever one of the lights is seen.
• The machine prints out a report that maps any blanked-out areas in the person’s vision.

Text Continues Below

---

The test is complex and lengthy; elderly people and those with short attention spans may be inappropriate candidates. Other perimetry tests, some requiring less time to administer and some using "virtual reality" techniques, are currently being developed.

Other Tests. Other visual field tests are being developed that can detect abnormalities years before they can be detected by standard perimetry. Experts recommend some of these tests in selected patients with suspected glaucoma.

For example, a screening test called frequency doubling technology (FDT) checks for changes in particular cells in the retina that are indications of early glaucoma. It takes less than a minute to perform.