Emmetropia

Emmetropia ( from Ancient Greek ἔμμετρος émmetros " to the extent ", " fit " and ὤψ ops "eye" ) is the ophthalmologic term for normal vision. One eye is called emmetropic emmetropic or if there is an optically infinitely distant object reflects sharp without accommodative effort. This means in the sense of geometrical optics that intersect parallel incident light rays (light source at a great distance ) exactly in one point of the retina.

Failure to do so is called a refractive error ( ametropia ) - which includes nearsightedness (myopia), farsightedness (hyperopia ) and astigmatism (astigmatism ).

The concept of emmetropia is an idealization that is useful both for theoretical understanding as well as practical correction of ametropia. In contradiction to the word " normal vision " is the average of the human eye in ametropic area.

For the work on optical instruments is a " normal- eye" is generally not a requirement, because most of the eyepiece is a diopter compensation. More importantly, here is the freedom of astigmatism (different refractive power of the eye vertically and horizontally ). Emmetropia is also no legal requirement for professions such as the commercial aircraft pilots, which ametropia of up to 3 diopters is permitted, the bus driver or skipper. Here, however, high demands are made to the visual acuity.