A visual field test is designed to find out how well your peripheral vision works. Reading an eye chart tests how well your visual system works in the central area but provides little information about your side vision. A visual field test examines both your central vision and your peripheral vision by measuring the sensitivity of your visual system in various positions
Central vision allows you to see the fine details of objects you are looking at directly. Peripheral vision is used to find objects and detect threats and is important for general orientation and balance. If you have poor vision on one side, you may tend to bump in to door frames. Driving may be very dangerous if you cannot see traffic in the lane next to you.
Peripheral vision is necessary in sport to be able to locate other players on a field or court, and to see the ball out of the corner of your eye.
Peripheral vision is also important for other tasks such as reading. For example, if you have poor vision on the right side you may find it difficult to read a line of type, as you cannot see the next word in the line. A person with poor vision on the left side may be able to read along the line but have difficulty finding the start of the next line.
Visual field defects can be caused by something that damages or interferes with any part of your visual system.
Causes of visual field defects can include injuries or diseases of the retina (the light-sensitive layer of cells at the back of the eye), and diseases such as glaucoma which damages the optic nerve that carries signals from the eye to the brain.
Other causes are brain injuries and strokes that damage the vision region of the brain.
Damage to different parts of the visual system causes different types of visual field defects. This makes visual field testing a very useful way of detecting and diagnosing many diseases.
The most common way of visual field testing is by using a computerised instrument called an automated perimeter. This consists of a concave bowl which allows lights to be flashed at various points inside the bowl. A computer controls the brightness of the lights.
During a visual field test, you sit facing into the bowl with your head resting on a support to restrict movement. One eye is tested at a time, with the other eye covered by an eye patch. You look directly at a light in the centre of the bowl and press a button each time you see a light flash elsewhere in the bowl.
The computer varies the brightness of the test lights and records when you respond by pressing the button each time you see a light. This allows the sensitivity of your visual system to be measured at each point.
Keep looking at the light in the centre of the bowl as this will keep your eye still. If your eye is moving around, it is not possible to tell which part of the visual field is being tested.
Sometimes the lights will be easy to see; sometimes they will be difficult. Do not worry if you do not seem to be seeing many lights. A person with completely normal visual fields usually will not see about one-third of the lights.
A visual field test can be bulk billed to Medicare for those who are eligible. This test does not attract a benefit from HCF.
Visit or call one of our centres if you are concerned about the health of your eyes or would like to book an appointment for an eye examination.
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