WHAT IS AN EYE REFRACTION TEST?
An eye refraction test is part of a routine eye examination and is usually performed as a vision test. The test will tell your physician the prescription needed in your glasses or contact lenses. The optimal value considered normal or perfect is 20/20. Individuals having 20/20 vision are able to read letters 3/8 of an inch at about 20 feet away. Individuals not capable of achieving 20/20 vision have what is called a refractive error. This would mean that the light is not bending properly when it passes through the lens of your eye. The test will tell your physician what prescription lens you should wear in order to achieve 20/20 vision.
WHY IS THIS TEST USED?
The results of the test will be used to diagnose the following conditions:
- Astigmatism - which is a vision problem caused by an error in the shape of the cornea, this in turn causes blurry vision.
- Hyperopia - this is also known as farsightedness, those with this condition can see distant objects very well but have difficulty focusing on objects that are up close.
- Myopia - this is also known as nearsightedness, those with this condition can see objects up close very well but struggle with faraway objects since they appear blurry.
- Presbyopia - this is an eye condition where your eye will slowly lose the ability to focus quickly on objects that are close and is a disorder that affects everyone during the natural aging process.
The results of the test can further help diagnose the following conditions:
- Macular degeneration - this is a condition that is caused by central vision loss. This is what you see when you're looking straight ahead, since your peripheral vision is what you'll see on the side when your looking straight.
- Retinal Vascular Occlusion - when the light that passes through the eyes is blocked or fluids are present because the occlusion can cause blood or other fluids to build up, this prevents the retina from properly filtering light. The result of this can cause a sudden loss of vision.
WHO SHOULD THE TEST BE FOR?
The test should is recommended for:
- Adults who are under the age of 60 and are visually healthy, those who are not experiencing vision problems should for refraction testing every 2 or 3 years.
- Children should have a test at least once every year or two, starting at around no later than 3 years of age.
- For those already currently wearing prescription glasses or contact lenses, you should then have a test every 1 to 2 years.
- For those who have diabetes then it is recommended to have an eye examination every year.
- If you're over 60 or have a family history of glaucoma then you should also have an examination test every year.
WHAT TO EXPECT
Your physician will first assess how the light bends as it moves through your cornea and the lens of your eyes. As such, this test will then help your physician determine whether or not you need corrective lenses and if so, what type of prescription you would need. In this stage your physician may just use a computerized refractor for this part of the test, or may simply shine a light into your eyes.
In the computerized test you will look through a machine that will measure the amount of light reflected by your retina, your physician will be able to do this test without the help of the machine. As soon as it is done, your physician will determine the exact prescription you need. In the next part of the test you may be seated in front of a Phoroptor, which will look like a mask with holes for your eyes to look through, you will then face a wall with a chart of letters for adults and for children who cannot yet read letters, then a chart with small pictures of common items.
Your eye physician will then test each eye one at a time, asking you to read until the smallest row of letters that you can see. Your physician will change out the lenses on the Phoroptor, asking you each time which lens is clearer. If you are unsure, you can ask your physician to repeat the choices. When the test is complete for one eye the procedure will repeat for the other eye, when the whole procedure is finished your physician will calculate the combination that comes closest to giving you 20/20 vision.