REFRACTIVE CONDITION OF EYE
If the refractive power of the optical components of the eye, primarily the cornea and lens, correlate with the distances between the cornea, lens, and retina so that incoming parallel light rays come into focus on the retina, a clear image will be seen. This condition is called emmetropia.
No correction is necessary for clear distance vision.
In hyperopia (farsightedness), the distance from the cornea to the retina is too short for the refractive power of the cornea and lens, thereby causing images that would come into focus behind the retina.
Hyperopia can be corrected by placing a convex lens in front of the eye to increase
the convergence of the incoming light rays. In myopia(nearsightedness), because the lens and cornea are too strong or, more likely, the eyeball is too long, parallel light rays are brought into focus in front of the retina.
Myopia can be corrected by placing a concave lens in front of the eye, causing the incoming light rays to diverge.
OPTOMETRY-SHARP VISION
Optometrist