What is a refraction?
Refraction is a test by which your optometrist can determine which lens combination will help you to see the best. Refraction can be done in a number of ways.
The method with which you may be most familiar is when the optometrist holds up a number of lenses and asks you which gives you the best vision, or visual acuity, this is a subjective refraction. Tests of refraction therefore are not tests of visual acuity but tests designed to establish your prescription.