A Visual Field includes both the central and peripheral vision. A typical person’s visual field usually extends 60 degrees superior, 75 degrees inferior, 60 degrees nasally and 100 degrees temporally. People are usually not conscious of their peripheral visual field – only what’s most sensitive and that is centrally. There is an absolute blind spot also known as a scotoma, which is on average 15 degrees temporally, this is where the optic nerve is located.
What is a Visual Field Test?
A visual field test measures the integrity and functionality of the optic nerve and the optic nerve pathways. These include the optic nerve chiasm, optic tract, lateral geniculate nucleus and the visual cortex in the brain. A visual field test is essential in diagnosing and monitoring both visual and neurological disorders affecting the visual system.
How is a Visual Field Test performed?
The technician doing the testing will instruct you to look straight ahead at a central fixation point during the entire duration of the test. Each eye will be tested separately. The eye not being tested will have an eye patch placed on it. While you are looking straight ahead, lights of different brightness will be shown in the peripheral visual field. The technician will instruct you to click a button when you see these lights. By doing this, all parts of your central and peripheral vision will be mapped out by the computer. This can show any lesions or abnormalities along the entire visual pathway.
What types of Eye Diseases show a Visual Field Loss?
Some of the ocular diseases or situations that can cause a visual field loss include (but are not limited to):
- tumours in the brain (pituitary tumours)
- macular degeneration
- patients on plaquenil therapy
- retinal conditions such as retinitis pigmentosa
- optic nerve head swelling (papilledema)
- retinal detachments
- optic neuritis (sometimes seen in MS)
It is important to know that many ocular diseases cause a loss of peripheral vision loss without the patient knowing they are losing their peripheral vision as visual field loss occurs slowly over time. For example, Glaucoma is often called the “silent thief” as it robs patients of their peripheral vision slowly over time without their knowledge until it’s very severe and too late.
What kinds of treatments are available for Peripheral Vision Loss?
Treatments can vary depending on the reason for the visual field loss. In glaucoma for example, once the visual field loss has occurred, one can never gain back that lost vision. Treatment is aimed more at preventing more visual field loss usually in the form of eye drops or surgery. In other ocular conditions where visual field is lost, treatment can include using optical aids such as a prism to increase the field of view or move objects in the periphery more centrally. Other visual aids can include magnifiers or line readers. Another treatment option includes training or therapy to help one see better in their peripheral vision.
Due to the fact that most visual field defects are silent in nature, it is important that you are examined regularly (every 1-2 yrs for adults and annually for children and seniors) to ensure there are no underlying eye diseases taking away your central or peripheral vision. We have a machine which can test your visual field at our Huntington Hills office in Calgary. When you have an eye exam at any of our offices all over Alberta, if your doctor deems it necessary that you get a visual field done, you will be referred to one of those two locations to get the testing done. Click here to book your eye exam today!