Visual fields are important in neuro-ophthalmology to determine not just the peripheral vision of a patient but also the central vision. They are an extremely sensitive psychophysiological test. We can determine if the patient’s optic nerve function is worsening depending upon how a patient does on a visual field test. This can be tracked over time and can be quantitated.
You will be asked to perform many visual fields. We have several different types of visual field tests. The simplest of them is an Amsler grid. An Amsler grid is a test of the central visual field. A grid of graph paper is placed in front of one eye and you are asked to describe any distortions of the straight lines in the graph paper or any areas that are missing. This is done for each eye.
The next most complicated visual field test is done with an Arc perimeter. In an Arc perimeter you are asked when you first see a moving target coming in at different angles. It is particularly useful in determining whether or not a patient’s range of single binocular vision is increasing. It can also be used to measure head turns, face turns, and position of the chin. It can be used to quantitate whether surgery for these problems has resulted in improvement.
Tangent visual fields are performed at either 1 or 3 meters or both. They are particularly useful in patients with severe head injuries. A moving target is shown to the patient and they are asked to respond when they first see the moving target on a flat background.
Goldmann visual fields are performed under strict technician supervision. Targets of various intensities are presented to the patient, either moving or stationary. The visual field is plotted first for one eye and then the next.
An Oculus visual field can be used to determine the visual threshold for a stimuli. A frequency doubling technology field obtains the most sensitive screening test for visual loss. In this type of test the gratings of increasing subtlety are presented for the patient to see. We determine a threshold at which the patient sees these gratings. In an Octopus visual field, we have the potential to use different types of colors to measure different photoreceptor responses. For example we can test the blue-yellow threshold which is particularly useful in tests of optic nerve function.
The Humphrey visual field gives the threshold with the central 24 or central 30 degrees and can be used to monitor long term trends.
All are easy to perform and are performed in subtle lighting conditions called scotopic conditions. They are performed one eye at a time. A patch will be placed over one side and you will be given instructions. Each of these tests will be frustrating at times, as the computerized tests will try to trick you. The programer will retest certain areas to make sure that your responses are correct.