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Perimetry


Perimetry is the systematic measurement of visual field function (the total area where objects can be seen in the peripheral vision while the eye is focused on a central point). The two most commonly used types of perimetry are Goldmann kinetic perimetry and threshold static automated perimetry. A visual field test (perimetry) will detect loss of peripheral vision and provide a map of that loss which will be helpful in diagnosing the cause of the loss. A perimetry test (visual field test) measures all areas of your eyesight, including your side, or peripheral, vision.

Perimetry is the systematic measurement of visual field function. The two most commonly used types of perimetry are Goldmann kinetic perimetry and threshold static automated perimetry. With Goldmann or "kinetic" perimetry, a trained perimetrist moves the stimulus; stimulus brightness is held constant. The limits of the visual field are mapped to lights of different sizes and brightness.

With threshold static automated perimetry, a computer program is selected. The most commonly used one tests the central 30° of the visual field using a six degree spaced grid. This is accomplished by keeping the size and location of a target constant and varying the brightness until the dimmest target the patient can see at each of the test locations is found. These maps of visual sensitivity, made by either of these methods, are very important in diagnosing diseases of the visual system. Different patterns of visual loss are found with diseases of the eye, optic nerve central nervous system.

To do the test, you sit and look inside a bowl-shaped instrument called a perimeter. While you stare at the centre of the bowl, lights flash. You press a button each time you see a flash. A computer records the spot of each flash and if you pressed the button when the light flashed in that spot.

At the end of the test, a printout shows if there are areas of your vision where you did not see the flashes of light. These are areas of vision loss. Loss of peripheral vision is often an early sign of glaucoma.

Why It Is Done

A perimetry test can help find certain patterns of vision loss. This may mean a certain type of eye disease is present. It is very useful in finding early changes in vision caused by nerve damage from glaucoma.

Regular perimetry tests can be used to see if treatment for glaucoma is preventing further vision loss.

Results

The amount of peripheral vision loss is linked to the amount of optic nerve damage. A perimetry test makes a detailed record of your visual fields. Baseline information, descriptions, or drawings can be compared with future test results.

What To Think About

A perimetry test is a good test to find vision loss caused by glaucoma. A perimetry test can be done quickly, but it may take more than 45 minutes when both eyes are tested.

image of perimetry eye test
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