Visual field testing (VFT) is a group of sophisticated and automated tests that measures both the central peripheral (side) vision of an individual. The visual field is the entire area one can see. Changes in the visual field may be difficult to notice since both eyes are generally used at the same time. One eye can sometimes compensate for some vision loss in the other. A problem may not be detected until each eye is tested separately. A visual field test may detect:
- Any problems with vision in any part of the visual field
- Study blind spot
- Diagnose, document, or treat neurologic or eye disease
- Vision loss or obstruction for functional purposes
- Any damage to the optic nerve (The optic nerve is a bundle of nerve fibers that are part of the central nervous system. They serve as a communication cable between the eyes and brain. When the optic nerve is impaired, the ability to send the messages and signals through the nerve may also be impaired.)
It helps in diagnosing below conditions as well:
- Glaucoma: It is a severe condition in which the optic nerve is progressively damaged because of high eye pressures. Even after glaucoma treatment has been commenced, visual fields are performed every 6-12 months to ensure that the peripheral vision is not deteriorating despite treatment. If so, then treatment needs to be changed or escalated.
- Optic neuropathy: Any disease that affects the normal functioning of the optic nerve is called optic neuropathy. Swelling (optic neuritis) or ischemia (ischemic optic neuropathy) are common types of optic neuropathy and can result in significant loss of central and peripheral vision.
- Stroke: Strokes (cerebrovascular events) are usually due to a sudden loss of circulation to vital areas of the brain. Strokes can generally be ischemic (blockage of circulation) or hemorrhagic (bleeding of circulation, but both result in significant damage to brain function). The visual pathway may be affected by a stroke, resulting in the loss of specific areas of the peripheral visual field. Often specific patterns of field loss will help pinpoint where in the brain the stroke has occurred.
- Toxic reactions from various medications: VFT is being increasingly used to help detect and monitor side effects in the eye from various long-term medications. For example, Plaquenil, often used for autoimmune conditions like rheumatoid arthritis and lupus, may affect the macula, resulting in central vision loss. Regular eye tests are recommended for any patient on Plaquenil.
- Driving assessments: When peripheral vision is reduced by certain diseases of the eye or brain, VFT can be used to assess if the patient meets safe driving standards. Certain specific criteria for central and peripheral vision need to be met for an unrestricted driving license to be maintained.
- VFT can also help in detecting brain tumors, brain swelling, brain injuries, autoimmune diseases, such as multiple sclerosis and thyroid abnormalities.
What are the common types of visual field tests?
The common types of visual field tests include:
- Confrontation exam: In this test, the doctor sits directly in front of the patient and asks them to cover one eye. They may need to look straight ahead and tell the doctor each time they see the doctor’s hand moves into view.
- Manual testing (tangent screen and Goldmann exams): In this test, the patient usually sits a short distance from a screen and focuses on a target at its center. They need to tell the doctor when they can see an object move into the peripheral vision and when it disappears.
- Automated perimetry: In this test, the patient may need to look at a screen with blinking lights on it, they may be asked to press a button each time when they see a blink. Each eye is tested separately. It assesses peripheral vision.
- Kinetic visual field testing: This test is like the automated perimeter test, but it uses moving lights instead of flashing lights.
- Electroretinography: This test measures the electrical signals of the light-sensitive cells (photoreceptors) in the retina to identify vision loss from certain retinal conditions.
- Frequency doubling perimetry: An optical illusion of black and white lines is used to detect vision loss. These lines will flicker at differing times and rates through the test. If you are unable to see the lines clearly throughout the test, you may have vision loss in parts of your visual field.
- Amsler grid: It is used for people with age-related macular degeneration (AMD). This test contains a pattern of straight lines in the form of a grid. You must look at a dot in the middle of the grid, if any areas that appear blurry, wavy, dark, or missing, it means loss of central vision.
It often takes two or three tests to get good enough reliable answers.