refractive
A refraction is the process by which an eyecare practitioner measures the eyes to determine the proper prescription for eyeglasses, contact lenses, or surgical vision correction. "Refractive" refers to this process, as in the phrase "refractive eye exam." "Refractive error" means that light entering the eye encounters an aberration that prevents it from reaching the proper spot on the retina; the result is blurry vision.