Simulation of hypermetropia (long sightedness). Shows normal eye becoming hypermetropic 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 shortens to simulate a hypermetropic eye and the rays now come to a focus behind the retina. A correcting lens is then dropped into place and the rays are brought to a focus on the retina.
Hypermetropia is a refractive error. The hypermetropic eye is relatively too short (along its visual axis) for the converging power of its optics. Consequently it cannot focus distant (parallel) rays on the retina (compare with a myopic eye). Such rays converge behind the retina. Hypermetropia is corrected by using spectacles with converging (convex) lenses.