EMMETROPIA

From Big Medical Encyclopedia

EMMETROPYYa (emmetropia; the Greek emmetros measured proportional + ops, opos of eyes; synonym: an emmet-ropichesky refraction of an eye, a proportional refraction of an eye) — one of types of a clinical refraction of an eye which is characterized by the fact that the parallel rays of light getting into an eye after refraction are focused precisely on a retina.

In view of this feature E. call normal, or proportional, a refraction of an eye, opposing it to short-sightedness (see) and far-sightednesses (see), to-rye carry to disproportionate refractions, or a so-called ametropia (see the Refraction of an eye). AA. does not assume surely in all cases of an identical structure of the eyes identical of the radius of curvature of a cornea, length of an eyeglobe and other factors influencing a refraction of an eye; on the contrary, big individual fluctuations are in this respect observed (see an Eye, dioptrics), but these factors are mutually combined at E. so that eventually the optical system of an eye is proportional, em-metropichesky.

At E. usually high visual acuity equal 1,0 is noted, and it is frequent, especially at people of young age, even above. A further point of clear sight (see) at E. is in infinity since the rays of light going from infinity are parallel. Thus, thanks to the optical device of eyes people with an emmetropichesky refraction well see afar as coincidence of focus of parallel beams to a retina provides a sharp image of the considered objects that is one of the main conditions of a high level of sight. People with an emmetropichesky refraction usually well see and at a short distance, however it is already carried out by means of the act of accommodation of an eye (see). If the person with an emmetropichesky refraction has the sufficient volume of accommodation as it usually happens at young age, he well sees in very big limits of space — from a further point yasnogo1 sight, lying at E. in infinity, to a so-called next point of clear sight, situation the cut is defined by the maximum tension of accommodation. At persons of young age with E. the closest point of clear sight lies usually at distance of several centimeters before, an eye and therefore the range of good sight of an emmetropichesky eye (on condition of preservation of accommodation) is very big — from infinity to several centimeters before, an eye (e.g., at the age of 10 years at distance of 7 cm, at the age of 20 years —

10 cm). Difficulties during the work at a short distance at persons with E. appear by 40 — 45 years when accommodation begins to weaken naturally.

Bibliography: The multivolume guide to eye diseases, under the editorship of V. N. Arkhangelsky, t. 1, book 1, page 275, M., 1962; Der Augenarzt, hrsg. v. K. Velhagen, Bd 2, S. 224, Lpz., 1959. M. JI. Krasnov.

Яндекс.Метрика