Vision Testing

During an eye test, many aspects of vision are assessed, not only to determine how well the eyes see, but how hard the eyes are working to see. 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.

If there is a refractive error e.g. short sightedness (myopia), long sightedness (hyperopia) or astigmatism, it means the eyes don't focus properly. This 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. This makes the eyes see as clearly as possible. Other tests will be performed to look for other conditions, such as testing that the two eyes work together properly (binocular vision), 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 objects in front of us. We also need side or peripheral vision to see things that are above, 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 such as the police.