With this procedure your optometrist will determine your exact prescription for a pair of eyeglasses . During a refraction, your eye doctor puts the phoropter in front of your face at eye level and chooses you a series of lens choices. He or she will then ask you which of the two lenses in each choice ("1 or 2," "A or B," for example) make the letters on the Snellen Chart appear sharper.
Depending what your answer, your eye doctor will evaluate the degree of nearsightedness, farsightedness and/or astigmatism you may be suffering from. They will also prescribe a set of eyeglasses to help correct these vision problems (which are called refractive errors).