From Big Medical Encyclopedia

SKIASKOPIYA (Greek skia a shadow + skopeo to consider, investigate; synonym: pupilloskopiya, retinoskopiya, shadow test, fantoskopiya) — an objective method of definition of a clinical refraction by overseeing by movement of a light spot in the lit pupil at rotation of an oftalmoskopichesky mirror.

It is offered in 1873 by the fr. medical officer Kyuinye (F. L. J. Cui-gnet). The term «skiaskopiya» is not absolutely correct since at this research observe the movements of a light spot, but not shadows. Along with other objective methods of definition refractions of an eye (see) S. it is irreplaceable at assessment a wedge, refractions at small children, at amblyopias (see), and also for identification simulations (see).

Fig. 1. Outward of a pupil of an eye at a skiaskopiya: the light spot in the field of a pupil is specified by an arrow.

For an explanation of patterns of movement of a light spot (fig. 1) in the lit pupil at turn of an oftalmoskopichesky mirror several theories are offered, the greatest recognition from them was gained by the theory of a skiaskopiya of Landolt — Parana. According to this theory blackout of a part of a pupil corresponds to a dark part of an eyeground, edges it appeared in a shadow at rotation of a mirror and shift of the field of oftalmoskopichesky lighting. Blackout is caused by the fact that the iris of the studied eye, being on the way of light rays, detains a part them.

The direction and speed of the movement of a light spot at S. depend on what mirror (concave or flat) send a ray of light to a pupil of the studied eye, from distance, on Krom there is a doctor from the patient and, at last, from a wedge. refractions of the studied eye.

At S. use a plane mirror (skiaskop) more often, a cut has advantages before concave since provides uniform illumination of a pupil and does not take detours of light scattering around a light spot. Use of the light source concluded in special devices — elektroskiaskopa is possible.

The village should carry out 1 m as at the same time it is simpler to make calculations from distance and it is easier to avoid mistakes during the definition of a myopia of high degree (see. Short-sightedness ). At emmetropias (see), hypermetropias (see. Far-sightedness ) and myopias less than 1,0 dptr the light spot in the field of a pupil moves in the direction of the movement of a mirror if it flat, and to the opposite side if it is concave. At a myopia more than 1,0 dptr the light spot moves in the direction of the movement of a mirror if S. carry out by a concave mirror, and to the opposite side if S. carry out by a plane mirror. At a research of an eye with the myopia equal 1,0 dptr, the movement of a light spot is not noted since an eye of the researcher is located at the same time in to a further point of clear sight (see) the studied eye.

In a crust, time at S. apply a way of neutralization of movements of a light spot lenses, to-rye change the direction reflected from a retina of the studied eye of beams. When the lens facing the studied eye as if turns it in miopichesky degree 1,0 dptr, the movement of a light spot stops since in this case all beams, coming from the studied eye, will surely get into an eye investigating, and the pupil or will be lit, or at once will darken.

Fig. 2. Set of skiascopy frames: 1 — it is linear with negative lenses (from 1,0 to 9,0 dptr); 2 — a ruler with positive lenses (from 1,0 to 9,0 dptr); 3 — a cursor with negative lenses (0,5 and 10,0 dptr); 4 — a cursor with positive lenses (0,5 and 10,0 dptr).

Apply skiascopy frames (fig. 2) consisting of positive and negative lenses from 1,0 to 9,0 dptr to convenience of carrying out S. For best accuracy in definition of ametropias of high degrees cursors with lenses 0,5 and 10,0 dptr are applied to rulers. Degree of a refraction is defined to within 0,5 dptr.

Usually S. carry out under the same conditions, as an indirect ophthalmoscopy (see. Oftalmoskopiya ). The doctor sits opposite to the patient at distance of 1 m and by means of a ski-askop lights a pupil of the studied eye, turning skiaskop around a horizontal and vertical axis, watches the nature of the movement of a light spot. By the rules described above the wedge, refractions, and then define a look by skiascopy frames — its degree. The refraction is calculated on a formula: Р = ±С + (-1,0), where P — a refraction of the studied eye (in dptr); With — the refracting force of a lens (with a sign + or — in dptr), during the use the cut disappears the movement of a light spot in the lit pupil and the refraction of an eye as if becomes equal — 1,0 dptr. At an astigmatism (see. Astigmatism of an eye ) definition of a refraction is carried out separately in two main meridians. More exact results at an astigmatism can be received by means of a tsilindroskiasko-piya — a method, at Krom apply cylinder lenses to neutralization of the movement of a light spot. For this purpose use a trial frame, in to-ruyu at S. at the same time establish both spherical, and cylindrical lenses. For specification of results of S. at an astigmatism use a stroke-skiaskopiyu, or striate S., at a cut in the studied eye project a beam of light by means of the special device — the striate skioskop or a stroke-skiaskopa allowing to orient a light flux in any meridian of a cornea.

Other methods increasing the accuracy of a skiaskopiya are S. in infrared light and S. with use of the blinded light source (fotoskopiya).

Bibliography: Avetisov E. Page and P about-z e N of l yu m Yu. 3. Optical correction of sight, M., 1981; Radzikhov-with to and y B. of JI. Astigmatism of a human eye, M., 1969; Titov of I. I. Skiaskopiya, L., 1941; Cuignet P. L. J. K^ratoscopie, Rec. Ophtal. (Paris), t. 1, p. 14, 1873—1874; Eye, ed. by H. Davson, v. 4, p. 1, N. Y. — L., 1962.

S.E. Avetisov.