From Big Medical Encyclopedia

HETEROPHORIA (heterophoria; Greek beteros of another, other + phoros bearing; synonym latent deviation) — a deviation of eyeglobes from the correct (symmetric) situation at an exception of conditions for solid vision.

The unequal force of action of oculomotor muscles (a muscular imbalance) is G.'s reason. Unlike explicit squint, at G. it is always kept solid vision (see).

Meets considerably more often (at 70 — 80% of people), than orpthophoria (see). In usual conditions thanks to fusional ability of the visual analyzer (see Fuziya) disturbance of muscular balance is not shown. During creation of the conditions excluding solid vision (if to cover one eye), relative weakness of any muscle therefore an eye deviates towards the antagonist of this muscle comes to light. At the same time the visual line of this eye deviates knutr (esophoria), knaruzh (exophoria), up (hyperphoria) or from top to bottom (hypophoria); the tendency to turn of top end of a vertical meridian of a cornea of a knutra (intsikloforiya) or knaruzh (ekstsikloforiya) is sometimes observed. The esophoria meets more often other types of G. Stepen G. determine by the size of a deviation of the visual line of one of eyes from a point of fixing and express in prismatic dioptries: 1Δ = 0,52 °.

G.'s recognition usually does not represent difficulties. If to close one eye investigated by a hand (an eye will deviate in this or that party), and then to open it, it does the adjusting movement aside, opposite to that, in to-ruyu was rejected. For definition of existence and G.'s character put a prism or Maddox's stick to one eye (see. Maddox stick , scale). Maddox's stick consists of a number of the small cylinders from red glass soldered among themselves. Light of a bulb is visible through it as a red line. Investigated suggest to look at a bulb, having put Maddox's stick to one eye. At G. the red line deviates in this or that party a bulb. The direction of a rejection of the image will be specified by G.'s type, and size of a deviation on a tangential scale (a special crosspiece with the divisions corresponding to tangents of corners at distance of a crosspiece from the studied eye 1 and 5 d) or force of a prism transferring the image to a point of fixing — degree of.

At G. visual work, especially at a short distance, demands bigger, than usually, neuromuscular tension for overcoming a tendency of an eye to a deviation. At high degrees of G. (7 — 8Δ more) and the weakened fusional ability it can cause asthenopia (see), shown bystry fatigue, headaches, nausea, passing diplopia (see). Emergence of these phenomena is promoted by the general diseases, intellectual overfatigue, anomalies of a refraction.

At emergence of an asthenopia creation normal a gigabyte is necessary. conditions of visual work, streamlining of a day regimen; at an ametropia and a presbyopy — purpose of a corrective spectacles and carrying out orthoptic exercises (on a synoptophore or by means of prisms) for recovery of fusional reserves. In the absence of success — glasses wearing with the prisms directed by top towards a deviation of an eye, or (in exceptional cases) operation on outside muscles of eyes.

See also Squint .

Bibliography: Avetisov E. S. Protection of sight of children, M., 1975; The Multivolume guide to eye diseases, under the editorship of V. N. Arkhangelsky, t. 3, page 274, M., 1962, bibliogr.; Sergiyevsky L. I. Concomitant strabismus and heterophorias, M., 1951, bibliogr.; Glaser T. Die Phorien, Ihre Prtifung und Korrektion, B., 1969; System of ophthalmology, ed. by S. Duke-Elder, v. 6, L., 1973.

E. S. Avetisov.