Visual Field Testing Can Reveal Many Eye Problems
What is visual field testing?
Visual field testing checks your visual field to detect any central or peripheral (side) vision problems that can be caused by glaucoma and other ocular disorders as well as brain dysfunctions. Many times, patients with visual field defects do not notice them especially if they are affected peripherally. If left untreated, these ocular disorders can lead to severe vision loss. Locating the field defect allows the doctor to determine which disease is causing the problem.
What conditions can it detect?
Visual field loss can occur in diseases that affect the retina, optic nerve, or brain. Visual field testing can aid in the diagnosis of glaucoma to help the doctor assess optic nerve damage. It can also reveal diseases of the retina (the light-sensitive membrane that lines the back of the eye), such as macular degeneration, retinal detachment, and retinitis pigmentosa. Many systemic diseases can cause retinal and/or optic nerve damage resulting in visual field loss such as diabetes, hyperthyroidism, hypertension and multiple sclerosis.
Problems caused by tumors in the eye or optic nerve, drooping of the eyelid (ptosis), and damage caused by an eye injury can also be detected. Visual field loss is not only caused by eye disorders; sometimes the origin of the problem is in the brain, such as a pituitary tumor or tissue damage after a stroke.
How is it done?
There are several different ways to test your visual field. In itís simplest form, confrontation field is performed. During this test, the doctor will sit or stand directly in front of you, and one of your eyes will be covered. You will be asked to fixate on the doctor with your uncovered eye, while he or she holds up different numbers of fingers off to the side. You will be asked when you can see the doctor's hand, and how many fingers you can see with your peripheral vision. The doctor will do this a few times, holding his or her hand in different places to test different areas of your visual field, and will then repeat the process for the other eye.
There is also the Goldmann field exam also known as Tangent Screen exam. During this test, you will sit approximately 3 feet from a screen which has a target in the center. You will be asked to stare at this target and let the examiner know when you can see an object that is brought into your peripheral field of vision. This test is no longer used because it requires a large space for testing.
The Amsler grid is used as another form of visual field testing. Unlike the two methods discussed above, this exam tests your central vision, not your peripheral vision, for defects. You will be given a black and white grid of squares with a black dot in the center. Holding the grid the same distance as any other reading material, with one eye covered, you will stare at the dot in the center of the grid, taking note of any part of the grid which appears distorted in any way. This may include wavy or blurry lines, blank areas, dark areas, or areas where the squares do not appear to be the same size. This central visual distortion is called metamorphopsia.
The Amsler Grid, shown here smaller than actual size, is one method of testing your visual field.
More sophisticated methods of visual field testing include:
Automated static perimetry - This test is computer-controlled to get more detailed and accurate results. For this exam, your head will be held still in a chin rest, usually in front of a device that looks like a white bowl. You will stare ahead at a small light in the center of the bowl, directly in front of you, while the device flashes lights in different areas of your peripheral vision, with varying intensities. You will be asked to indicate when you see these lights, usually by pressing a button. Automated static perimetry is usually used by ophthalmologists to diagnose and treat visual field defects.
Frequency doubling analysis - During this test, you will sit in front of a screen, where vertical bars of contrasting colors are quickly flashed. This test relies on an optical illusion: if the bars are flashed fast enough, they will appear to double in number. If you are unable to see the vertical bars or are otherwise unable to experience the illusion, that could indicate a defect. Frequency doubling analysis is commonly used in optometry offices to screen for visual field disorders.
Testing relies on patient cooperation
One of the problems with visual field testing is that the results are only as accurate as the patient allows, unlike something like a blood test, which is not subjective. If you will be undergoing visual field testing, try to schedule your appointment for a time you will not be tired. Fatigue can cause you to be distracted and miss things you otherwise would have seen. Also be sure that you listen carefully to all instructions given by the examiner, so that you will respond appropriately during the test.
If you believe you are experiencing blind spots or other problems with your vision, see your eye doctor as soon as possible for a complete exam. Many eye diseases worsen over time and can cause permanent vision loss if not diagnosed in time and properly treated.