Emmetropia

Emmetropia (from Greek emmetros, "well-proportioned" or "fitting", + -opia) describes the state of vision where a faraway object at infinity is in sharp focus with the eye lens in a neutral or relaxed state. This condition of the normal eye is achieved when the refractive power of the cornea and the axial length of the eye balance out, which focuses rays exactly on the retina, resulting in perfect vision. A human eye in a state of emmetropia requires no corrective lenses; the vision scores well on a visual acuity test (such as an eye chart test). For example, on a Snellen chart test, emmetropic eyes score at "6/6"(m) or "20/20"(ft) vision, whereas myopic (near-sighted) eyes might score at 20/40 and hyperopic (far-sighted) eyes might score at 20/15.