In the specialized field of ophthalmology, doctors measure sight by having you focus on a central point while keeping your head still. You’ll also be able to see above and below the central point and to either of its sides. Your vision will fade off at a certain point in all directions.
The area that you can see at one time without moving your eyes is called your field of vision or visual field. It may seem quite basic, but being able to name, analyze, and understand your field of vision is important in a medical setting.
Visual field tests can help your doctors get a better understanding of your vision.
Why Would You Need A Visual Field Test?
You may need a visual field test to help your doctor monitor or see signs of certain diseases like glaucoma. In the earlier stages of glaucoma, you may lose peripheral vision without realizing it, and a visual field test can help you manage your condition or start treating it.
The results of a visual field test can tell your doctor more about your eye health but also point to other issues. Your retina — a nerve cell layer that lines the back inside of your eye — is connected to your optic nerve, which is connected to your brain. So if you have an abnormal visual field, there may be problems in your optic nerves or your brain.
The visual field tests are designed so that your ophthalmologist can identify which vision problems are linked to which conditions. If you get tested regularly, your doctor can figure out which specific types of disease or injuries you may have.
What Do Visual Field Tests Diagnose?
Visual field tests help your doctor figure out whether you have blind spots, where they are, and what their shape is. This can tell you a lot about how an eye disease or brain disorder affects you.
Visual field tests can also diagnose issues with your eyelids.
What Are the Types of Visual Field Tests?
There are six main types of visual field tests. For each of them, you sit still while your doctor tests you.
The types are:
- Confrontation visual field test. You wear a blindfold while your doctor holds up different fingers in your peripheral vision and asks what you see.
- Automated static perimetry test. This test is much more detailed. Your doctor uses it to make a complete image of your field of vision. They cover one eye with a patch as you look into a tool called a perimeter. You press a button when you see a light blink. This test can tell your doctor about which lights and what level of dimness you can or can’t see.
- Kinetic visual test. This test is very similar to the previous one but uses moving lights instead of blinking lights.
- Electroretinography. Electroretinography measures vision loss because of problems with your retina. It measures the electrical activity in your eye as it takes in light. The doctor uses drops to dilate your pupils and numb your eyes. They hold your eyelids open with a speculum and put an electrode on your cornea. You look into a circular machine that flashes different patterns of light.
- Frequency doubling perimetry. In this test, your doctor shows you an optical illusion to check for damage in your visual field. It includes vertical bars — which are generally black and white — on something called a perimeter screen. These bars are set to flicker at various speeds. If you can’t see the vertical bars at certain time points of the test, you may have loss in certain parts of your field of vision.
- Amsler grid. You can do this test at home. Generally, it looks for age-related issues with the visual field. You look at a dot in the middle of a grid and note what parts of the grid you can see and which parts look wavy.
When Should You Get Your Visual Field Tested?
It’s important to get your visual field tested if you have a condition that might put your vision at risk, such as: