From Big Medical Encyclopedia

FUZIYa (fr. fusion merge) — the physiological mechanism of sight providing merge of two monocular pictures in a uniform visual object.

In the mechanism F. allocate two components: motive (optomotor fusional reflex) and touch (actually F.). An idea of a fuziya is given by experience with prisms. If at binocular fixing of a subject to put a prism to one eye, then the image of a subject in this eye will be displaced from the central site of a retina, i.e. it will be located in relation to other eye not on corresponding (identical), and on disparant-number (asymmetrical) site of a retina, and doubling will result. To get rid of it, an eye makes the fusional movement, and the image in it moves on the central site of a retina again. As soon as it occurs, the touch component F comes into effect. — the psychophysiological act of combination of two monocular images in a whole.

The fusional movements can be made only in the known borders, to-rye designate as amplitude, width F. or fusional reserves. Amplitude F. is defined by that maximum size of convergence and divergence (see Divergence of eyes, Convergence of eyes), and also supra-and infravergention. at a cut still perhaps binocular merge. Fusional reserves towards convergence and divergence call respectively positive and negative; aside supra-and infravergention (vertical reserves) — right and left supra-and infrafuzionny reserves depending on what eye is rejected respectively up or from top to bottom. Positive width F is normal. (for a distance and for a bliza) makes 24 — 28 prismatic dioptries, the negative width of a fuziya for a distance —

7 — 8, for a bliza — 16 — 18, the vertical width of a fuziya — 3 — 4. Sufficient durability and width F. provide stability of solid vision (see).

Disturbance F. can arise at sharp decrease in sight (see), a considerable difference in the size of images on retinas of both eyes (see Lnizeykoniya), at paresis of the nerves providing the movements of eyes at defeat of central office of solid vision. Visible manifestation of disturbance F. often squint is (see).

Research F. carry usually out on a synoptophore (see the Orthoptics). Merge of images of the objects shown separately to each eye demonstrates existence F. In this case determine width by the synoptophore or prisms established before eyes F. on the moment of approach of permanent doubling at movement of objects of a synoptophore or at gradual increase in force of prisms.

Recovery of normal amplitude F. — one of important problems of orthoptic treatment of squint and a heterophoria (see).

Bibliography: Avetisov E. S. I will erase

zhestvenny squint, M., 1977; B e l of wasps of t about c to and y E. M. Diagnosis and treatment of a concomitant strabismus at the present stage of knowledge, M., 1960.

E. S. Avetisov.