Emmetropia

EMMETROPIA, emmetropia (from Greek eu-good, metron-measure and ops-eye), according to Donders' terminology, such a clinical refraction of the eye, in which the eye can be considered proportionally constructed, i.e., there is a strict correspondence between the two factors determining the clinical refraction of the eye-the refractive power of the dioptric apparatus and the length of the eye's axis. The refracting apparatus has exactly the power required for an eye of a given length, i.e., so that parallel rays entering such an eye, after refraction, converge precisely on the retina. Such an eye, according to its physical structure, is adjusted for infinity, and therefore an emmetrope without any aids sees objects that are at such a distance from it that the rays emanating from them can be considered parallel. This proportional refraction is considered normal. E., being an ideal refraction, is in reality far from being the most common. Small deviations from the strict correspondence between the dioptric system and the length of the eye are usually present, and the most common refraction in reality turns out to be weak degrees of hyperopia. In life, emmetropic eyes provide maximum convenience and work capacity until, with age (approximately from 45 years), the decrease in elasticity of the lens reduces the accommodative power of the eye. Until that time, the emmetrope sees both far and near perfectly well, without needing any glasses.