Visual Field Testing
November 10, 2022
There are two important measures of vision that are typically taken to assess visual function. These are the visual acuity and visual field. The acuity is the test where you read down a (Snellen or Logmar) chart and this is a measure of the eye’s ability to discriminate between two points. This is what gives you your reading, colour and distance vision.
The peripheral vision is usually less distinct (which is why you use central vision for reading) and instead is useful for navigation. For example you use peripheral vision so you can get through a door without bumping into the edge of it or so that you can see an object coming towards you.
This test is performed using a visual field analyser and usually takes a few minutes to do. Typically, the test involves putting your head in a ‘bowl’ and pressing a button each time you see a flash of light. It builds up a picture of which areas of the peripheral vision are missing and can be abnormal in conditions such as a stroke, glaucoma, retinal detachment or any other condition which may affect all or part of the peripheral vision. Both the acuity and field of vision are tested together, especially when certain conditions are suspected.
It is helpful when coming to the eye department to always bring your glasses or most recent glasses prescription with you from your own optician as typically a lens is placed in front of the eye when performing this test.
The test we do for a condition which affects the eyes separately requires the two eyes to be tested separately, one after the other.
If diagnosed with glaucoma, you must inform the DVLA and they will require a ‘binocular test,’ which tests your field of vision with both eyes open and is a little more realistic in the real world situation of driving.