FIELD OF VISION

From Big Medical Encyclopedia

FIELD OF VISION — the space which is at the same time perceived by an eye at a motionless look and the fixed position of the head.

P.'s perception z. it is provided with the complex system of the visual analyzer allowing to find P. moving on the periphery z. an object, approximately to determine its sizes and a form — peripheral (bacillary) sight, and then to transfer immediately to the noticed object central (Coneal, fovealny) sight, a cut gives the chance to precisely establish a form, the sizes and color of the found object (see. Sight ). Thus, in P. z. it is possible to allocate the peripheral departments characterizing peripheral sight, and central, belonging to the central sight. Besides, allocate paracentral departments of P. z. Depending on that, one or both eyes participate in sight, distinguish a monocular and binocular field of vision. At solid vision (see) there is an imposing of nasal half of monocular P. z. Binocular P.'s borders z. is wider, than monocular P.'s borders z. In a wedge, practice usually investigate monocular P. z.

By the simplest method of a research P. z. the control method offered by F. Donders is. The research is conducted at uniform scattered lighting. One eye of investigated is closed an easy bandage. The doctor, being located opposite at distance with 1 m, closes an opposite eye. Investigated fixes a look an open eye of the doctor, and the doctor — an open eye investigated. Then the doctor carries out a finger of the hand in the direction from the periphery to a point of fixing, at the same time the finger shall be from the patient and the doctor equally spaced. The research is conducted in 4 main directions. Noting the moments when the finger becomes vidimykhm to the patient, define his P.'s borders z. Comparing borders of a field of vision of the field of vision of the doctor investigated with borders, a cut shall be normal, establish these or those deviations in P. z. investigated. This method is inexact and is only approximate.

The tool methods of a research based on fixing of the moment of emergence or disappearance of the test object shown to the patient on a spherical surface (an arch or a hemisphere) are most perfect — perimetry (see) or on the plane — kampimetriya (see). The perimetry is applied generally to studying of peripheral departments of P. z.; with its help define P.'s borders z., reveal defects of vision in these borders — scotomas (see. Scotoma ). Measurement of scotomas is performed in the way skotometriya (see). Kampimetriya allows to investigate the central and paracentral departments of a field of vision, to define localization and to measure the blind spot located in these departments, the central and paracentral scotomas.

P.'s borders z. vary depending on a structure of an orbit, size of a ridge of the nose, width of a palpebral fissure, degree of a vystoyaniye of an eyeglobe. Item z., defined in the presence of the natural limiters (acting parts of the face), call relative. At an exception of the limiting influences of speakers of parts of the face (it is reached by change of a point of fixing at the motionless head or the corresponding turn of the head) it is possible to receive absolute P. z., borders to-rogo approximately on 10 ° are wider than borders relative, from the temporal party these borders are not changed. P.'s borders z. brightness, colors, speeds of the movement of a test object, its contrast with a background, illumination of a background, and also from psikhofiziol, factors (visual or general exhaustion, light adaptation, individual psychomotor reaction of the patient) depends on size.

Fig. 1. The scheme of normal borders of a field of vision received as a result of perimetry of the left eye with use of white and color test objects. Borders of fields of vision for test objects are designated — white __________ color; blue _. _. _. _; red------; green _. _. _. _; the blind spot is shown to black.

The widest borders of P. z are normal. receive at a perimetrium with use of a white test object, a little already P.'s borders z. at a test object of blue color. Borders of a field of vision at a red test object already, than at blue. The field of vision investigated by means of a green test object has the narrowest borders (see the table and fig. 1).

Table. AVERAGE BORDERS of the FIELD OF VISION are NORMAL AT the PERIMETRIUM by means of VARIOUS TEST OBJECTS


In Item 3. there is a small site of an oval form where completely there is no vision — a blind spot, or Marriott's spot. It fiziol, scotoma, it corresponds to a projection of a disk optic nerve (see), in Krom there are no receptors perceiving light. The blind spot is located a pas-ratsentralno in a temporal half of P. z., on 15 ° lateralny points of fixing on a horizontal meridian. Its sizes at a kampimetriya from distance 1 on average 11,5 X 13,5 cm (or X 9 °). Along with a blind spot to fiziol, to scotomas carry the angioscotomas caused by existence of the vessels of a retina shielding her light-sensitive receptors. Fiziol, the scotomas revealed at a research P. z., do not break vision as P. z. one eye considerably blocks P. z. other eye, and also thanks to the micromovements of eyeglobes (see. Sight ).

Pathological changes of a field of vision are observed at the diseases of a retina, optic nerve, diseases of a brain which are followed by defeat of visual conduction paths or the visual centers. They are shown in the form of change of borders of P. z. or in emergence of various defects (scotomas) in these borders.

Fig. 2. Schemes of fields of vision, midday as a result of perimetry of the left eye with use of a white test object: and — at an end-stage of a pigmental degeneration of a retina (a tubular field of vision) — at far come glaucoma (sektoroobrazny loss of a field of vision), in — at amotio of a retina in a nishnenosovy quadrant (a dried field of vision of irregular shape); the sites which dropped out of a field of vision are shaded, a blind spot in fig., in is shown in black color.

Uniform narrowing of borders of P. z. in all directions — concentric narrowing — is noted at to glaucoma (see), an optic neuritis (see), peripheral chorioretinites, an initial stage of a pigmental degeneration of a retina (see. Tapetoretinalny dystrophies ). Considerably concentrically the narrowed P. z. (to 10 — 15 °) is called tubular, it is observed, e.g., in an end-stage of a pigmental degeneration of a retina (fig. 2, a). Such P. z. sharply complicates orientation in space, despite preservation of the central sight. P.'s narrowing z. can be sektoroobrazny (fig. 2, c). Such P. z. it is characteristic of glaucoma, nek-ry types of an atrophy of an optic nerve, an embolism of one of branches of the central artery of a retina, amotio retinas (see). Spiral P. z. (P.'s narrowing z. on a spiral) meets at nek-ry mental diseases (e.g., at schizophrenia). P.'s narrowing z. on blue color it is more often caused by pathology of a choroid of an eye, on red and green — pathology of visual conduction paths. Disturbance of a relative positioning of borders of color P. z. (inversion) often meets at glaucoma.

Great diagnostic value has identification of losses of half of P. z. — hemianopsias (see) and P.'s quadrants z. — kvadrianopsiya (quadrant hemianopsias) which meet at defeats of various departments of visual conduction paths and the visual centers (e.g., at tumors of a hypophysis, patol. processes in a back cranial pole).

Patol, scotomas can arise at damage of a retina, visual conduction paths, glaucoma and other diseases. Depending on situation in P. z. distinguish the central, paracentral and peripheral scotomas. The form and intensity of scotomas can be various (see. Scotoma ).



Bibliography: Merkulov I. I. Introduction to clinical ophthalmology, Kharkiv, 1964; The Multivolume guide to eye diseases, under the editorship of V. N. Arkhangelsky, t. 1, book 1, page 482, 492, M., 1962; Novokhatsky A. S. Clinical perimetry, M., 1973; Harrington D. Lake of The visual fields, St Louis, 1976, bibliogr.


Century of H. Marinchev.

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