Simulation of myopia (short sightedness). Shows normal eye becoming myopic and then being corrected.
The animation begins with a vertical section of a normal human adult eye focused on infinity (or a distant object) with the light rays parallel. The normal eye (at the very start of the animation) focuses the rays on the retina. During the first second, the eye elongates to simulate a myopic eye and the rays now come to a focus in front of the retina. A correcting lens is then dropped into place and the rays are brought to a focus on the retina.
Myopia is a refractive error. The myopic eye is relatively too long (along its visual axis) for the converging power of its optics. Consequently it cannot focus distant (parallel) rays on the retina. Such rays converge in front of the retina (compare with hypermetropia). Close objects (producing diverging rays) are focused properly (hence short sighted). Myopia is corrected by using spectacles with diverging (concave) lenses.