Vision Testing (acuity, refraction errors and field of vision tests)

During an eye test you are assessed for different things. A Snellen chart, which contains rows of letters starting with one huge letter then groups of letters getting progressively smaller, is used for visual acuity. An optometrist will establish how well you see without spectacles or contact lenses by getting you to read letters until they are too small or blurred to be recognised. They test each eye on its own and both together. Then the test is repeated while wearing your existing eye wear, this is known as your best corrected vision. Then the optometrist will ask you to remove your eye wear again and will see if your ability to read letters can be improved using lenses of different strengths for each eye until your eye sight is as good as it can be. If these new lenses are a different strength from your current spectacles you are given a new prescription and new lenses will be made for you.

People usually wear spectacles to correct a refraction error. In these cases the person’s eye lens is incorrectly focused, making that person either long or short sighted. This fault is corrected by placing an external lens, spectacle lens or contact lens, in front of the eye so that what is seen reaches the correct area on the retina in the back of the eye. There are other tests to look for other conditions, so an optometrist can find a corrective lens that gets a person’s sight near to, or in excess of, 20/20 vision.

We use central vision to read and look at thing in front of us. We also need side or peripheral vision to see things that are above and below and to the sides. This is also assessed during an eye test as you need a good field of vision to drive a car and it is a requirement for certain professions like the police.