| Subject | Contents |
| Definition | An eye test that measures a person's ability to see an object at a specific distance. |
| Alternative Names | Eye test - refraction; Vision testing |
| How the test is performed | This test is performed in the ophthalmologist's or optometrist's (eye doctor's) office. You sit in a chair that has a special device (phoropter or refractor) attached to it and look through the phoropter at an eye chart approximately 20 feet away. The phoropter contains lenses of different strengths that can be moved into view. The eye doctor will ask if the chart appears more or less clear with the lenses that are in place. The eye doctor can determine if you have myopia ( nearsightedness ), hyperopia ( farsightedness ), an astigmatism (asymmetrical cornea), or presbyopia (inability to focus on objects that are close to you). The extent of vision difficulty can be determined. The information obtained from a refraction test allows the prescription for eyeglasses or contact lenses to be correct for each person. |
| How to prepare for the test | Avoid eye strain the day of the test (read in adequate light, get plenty of rest the night before the test). Discontinue contact lens use. Infants and children: The physical and psychological preparation you can provide for this or any test or procedure depends on your child's age, interests, previous experiences, and level of trust. For specific information regarding how you can prepare your child, see the following topics as they correspond to your child's age:preschooler test or procedure preparation (3 to 6 years) schoolage test or procedure preparation (6 to 12 years) adolescent test or procedure preparation (12 to 18 years) |
| How the test will feel | There is no discomfort. |
| Why the test is performed | This test can be done as part of a routine eye test to determine if a person has normal vision. When a person complains of blurred vision , this test can help determine the extent of poor vision . It can also be performed to help follow the progress of treatments or diseases of the eye. The test is used to prescribe glasses if needed. |
| Normal Values | A normal value is 20/20 vision (perfect vision; able to read 3/8 inch letters at 20 feet) |
| What abnormal results mean | myopia ( nearsightedness )hyperopia ( farsightedness )astigmatism (asymmetrical cornea) presbyopia (inability to focus on near objects that develops with age) Additional conditions under which the test may be performed:corneal ulcers and infectionsmacular degenerationretinal detachmentretinal vessel occlusionretinitis pigmentosa |
| What the risks are | There are no risks. |
| Special considerations | A complete eye examination should be done every 3 to 5 years if there are no problems. If vision becomes blurry, worsens, or if there are other noticeable changes, an eye examination should be scheduled immediately. After 40 years old (or for people with a family history of glaucoma ), eye examinations should be scheduled more frequently to test for glaucoma. Anyone with diabetes should have an eye exam at least once a year. People with refraction problems should have an eye examination every 2 to 3 years. |
| | |