A refraction test, sometimes just called a vision test, occurs during a routine eye exam. Not all eye exams test a patient's vision, but this one does. The goal is for the optometrist to determine exactly what glasses or contact lens prescription will give their patient 20/20 vision. An individual who has 20/20 vision can read letters less than half an inch tall from twenty feet away. Those who don't have 20/20 vision are experiencing a refractive error. When the light passes through the lens of the eye, it's not centering correctly on the retina. An eye doctor uses a refraction test to determine what lens will refract the light onto the retina, allowing an individual to have 20/20 vision. In addition to telling the doctor whether prescription lenses are necessary, it indicates the exact prescription lens the patient should be using. The test results can be used to diagnose age-related presbyopia, nearsightedness, farsightedness, and astigmatism.
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