CONVERGENCE OF EYES

From Big Medical Encyclopedia

CONVERGENCE OF EYES (Latin convergere to meet, approach) — the physiological act of the data of visual axes of both eyes on the fixed subject.

Fig. 1. Film registration of convergences of eyes: 1 — the provision of eyeglobes at a look afar (corresponds to the 1st shot); 2 — the provision of eyeglobes at installation of eyes on a short distance (a shot 3); 3 — return of eyeglobes to initial situation (a shot 36).
Fig. 2. The scheme of the photoscanning pupillogramma (record of the movement of eyes and change of size of a pupil) at convergence of eyes: width of white horizontal lines characterizes width of a pupil, change of an arrangement of white lines corresponds to the movement of eyes (along with clear movement of a knutra of visual axes of both eyes the reduction of width of pupils caused by convergence is visible).

To. top and bottom direct muscles of both eyes are carried out due to simultaneous reduction of internal straight lines and partly; is followed by narrowing of pupils — miosis (see) — and tension accommodations of eyes (see). These three reflexes are composed one difficult act of visual installation of eyes on a short distance (fig. 1). Distinguish the following types To.: 1) tonic, caused by a tone of outside muscles of both eyes; 2) the akkomodativny, connected with tension accommodations and caused by synchronous interaction between accommodation and convergence; 3) fusional, caused by a reflex of binocular fixing of an object; 4) proximal, arising at approach of an object to eyes. For unit To. is accepted the meter angle, i.e. a corner which visual line (see) forms with the perpendicular recovered from the middle of a bridge of the nose when eyes fix the point which is at distance of 1 m from them. So, at two meter angles of an eye converge to the point lying at distance of 0,5 m, etc. A state To. is determined by the closest point of convergence (normal it is equal to 6 — 10 cm) — to distance from the coming object to an outside corner of an eye-socket at the moment when one eye ceases to fix an object and begins to deviate knaruzh. Strengthened To. at a considerable hypermetropia and weakened To. at a myopia in some cases can lead to squint (according to meeting or dispersing). Maximum To., at a cut still perhaps binocular merge, characterizes the size of positive fusional reserves. Normal positive amount fuziya (see) for a distance and for a bliza makes 24 — 28 prismatic dioptries. Objective registration To. and changes of size of a pupil it is possible by method of the photoscanning pupillografiya (fig. 2).

Disturbance To. at nevrol, diseases submits the difficult optikomotorny act which is closely combined with accommodation and pupillary reflex (see) and to connect disturbance To. with a certain localization patol, the center in c. N of page it is not always possible. Believe that the cortical centers of installation of eyes on a short distance are localized near the visual cortical centers, and supranuklearny! the center — near a kernel of a third cranial nerve.

Disturbances To. are shown in the form of paralyzes (paresis) and spasms. Paralyzes and paresis To. can be an early symptom epid, encephalitis, and also meet at parkinsonism, a craniocereberal injury and tumors of a brain localized preferential in the field of a roof of a mesencephalon (chetverokholmiya) and a water supply system of a brain. Sometimes at the specified localization there is a spasm To.

At paralyzes To. are noted impossibility to turn eyeballs of a knutra and cross diplopia (see). With approach of the considered subject the distance between double images increases. The pupillary test and an akkomodatsionny reflex on approach of a subject quite often are absent. At paresis To. degree of the data of visual axes is reduced, doubling arises only at a certain distance of the considered subject from eyes. During the work at a short distance there are asthenopic complaints — eye and head pain, nausea, misting and doubling of letters during the reading (see. Asthenopia ). The closest point of convergence is located from eyes much further, than normal. Positive fusional reserves are reduced. Time of convergent movements is extended.

At a spasm To. it is noted considerably big, than degree of a convergence of visual axes and the diplopia of the same name is required for this distance. It quite often is followed by narrowing: a pupil — a miosis and a spasm of accommodation.

The distance between double images increases in process of removal of a subject from eyes.



Bibliography: Bykovo O. V. Sostoyaniye of convergence at the closed craniocereberal injury, Oftalm, zhurn., No., page 444, 1971, bibliogr.; With about to about l about in and O. N. Oftalmonevrologi I defeats of a mesencephalon, M., 1971, bibliogr.; Physiology of touch systems, under the editorship of G. V. Gershunn, p.1, page 64, L., 1971; Shakhnovich A. R. Brain and regulation of movements of eyes, M., 1974, bibliogr.


E. S. Avetisov.

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