The ideal refractive state of the eye is emmetropia. In an emmetropic eye the
refractive powers of the cornea and the crystalline lens combine to precisely focus parallel rays of light from a distant object onto the retina as a single point. The cornea plays the greater role in achieving this.
An eye whose refractive power does not produce this precise focus is ametropic, and is described as having a refractive error.
The goal of clinical refraction is to determine the strength of the corrective lens that will achieve this precise focus when placed in front of the eye.
Tags:
Refractive error