Visual Field Testing
Your eye exam may include visual field testing, also known as perimetry.
What is visual field testing?
Your visual field is all the areas you can see when focused on a central point. Visual field testing enables your eye doctor to measure the range of peripheral vision and detect any blind spots or vision spots which may have occurred.
What are the benefits of visual field testing?
Visual field testing determines if you have blind spots (scotoma) in the field of vision, and if so, where the blind spots are. The size and shape of the blind spot can show how a brain disorder or eye disease is affecting vision. If you have glaucoma, visual field testing shows any peripheral vision loss because of the disease.
Types of visual field testing
There are different types of visual field testing.
Confrontation visual field test
During this type of visual field test, your eye doctor will ask you to cover one eye while looking at a fixed object directly in front of you while they hold an object in your peripheral vision field, and then ask you to identify the object. This test is commonly used to determine if there are any issues in your visual field and if further, more advanced testing is needed.
Automated perimetry test
This type of visual field testing creates a map of your visual field, which is used to determine a specific diagnosis of an eye condition or monitor an eye disease.
You will be seated in front of a perimeter, which is a bowl-shaped device, and each eye will be separately tested. The device will have your optical prescription so that you can see your best while being tested.
While being tested, you will be instructed to keep your eye on a center target. Lights will flash in different areas of the bowl, and some will be brighter than others. When you see the flashing lights, you’ll be instructed to press a button. The number of lights for which you did not press a button or identify will be added up at the end of the test and compiled in a printable report.
The test includes flashing lights you should not be able to see, so don’t worry you notice there aren’t any flashing lights at times during the test. The reason for this is the test is designed to measure your visual threshold.
Kinetic visual field testing
This type of visual field testing is like the automated perimetry test, but instead of flashing lights, this test uses moving lights.
Frequency doubling perimetry
This test utilizes an optical illusion to detect loss of vision. Black and white vertical lines are shown on a perimeter screen, and the lines will flicker at different times and rates. If you can’t see the lines clearly during the testing, there may be vision loss in parts of the visual field.
This test identifies loss of vision from certain retinal conditions by measuring electrical signals of the photoreceptors in the retina.
Your eye doctor will insert special eye drops to dilate and numb the eyes, and while your eyes are held open with a speculum, and tiny electrode will be placed on the front surface of the eye. You will then look at flashing lights in the perimeter machine, and the electrode will measure the eye’s response to each flashing light.
This test uses a pattern of straight lines which form a grid with equal squares. You will be asked to look at a dot in the middle of the grid, and describe any lines are areas that appear wavy, blank, or blurry. This test is commonly used for people who have age-related macular degeneration and is something they can do at home. While it only measures the middle of the visual field, it can still be helpful to monitor changes in vision.