SCOTOMA

From Big Medical Encyclopedia

SCOTOMA (Greek skotos darkness + - oma) — the limited defect of a field of vision which is not reaching its borders. Distinguish physiological and pathological Pages.

the Image of physiological and pathological scotomas on the skotometrichesky schemes reflecting results of a research of a field of vision of the right eye by means of a kampimetr (skotometr) of Aulo-Plot (the cross designated a point of fixing): and — physiological scotomas: a blind spot (1), angioscotomas (2) — the central scotoma (3) and a blind spot (4); in — Byerrum (5) scotoma connected with a blind spot.

Normal at a research fields of vision (see) S. come to light physiological: blind spot (E. Mariotte's spot) and angioscotomas (fig., a). The blind spot for the first time described by E. Mariotte in 1668 represents the small site of a field of vision where completely there is no perception of light. This site corresponds to a projection of a disk optic nerve (see), in Krom there are no visual receptors. The angioscotomas reminding in a form of a branch of a tree are always connected with a blind spot. They are caused by an arrangement of vessels of a retina ahead of its light-sensitive elements. The sizes and a form of a blind spot and angioscotomas vary depending on conditions of a research a little — sizes, brightness and colors of test objects, illumination of the background, a psychoemotional state investigated, etc. Physiological S. at solid vision (see) subjectively are not perceived since fields of vision of the right and left eye are partially blocked. It is promoted by also constant involuntary micromovements of eyeglobes. Thanks to these movements, and also an arrangement of a blind spot in paracentral departments of a field of vision physiological S. often are not noticed also at monocular sight.

Pathological S. arise hl. obr. at defeats retinas (see), actually choroid of an eye (see), visual conduction paths and the centers (see. Visual centers, ways ). Carry to them also increased and changed in a form as a result of various patol. processes physiological scotomas. E.g., at a congestive optic papilla (see. A congestive nipple), a papillitis — neuritis of an optic disk (see), back to a staphyloma (see) against the background of short-sightedness of high degree increase in a blind spot is observed. Angioscotomas can increase in sizes at periphlebites of a retina, a diabetic retinopathy, to glaucoma (see), etc.

Among pathological S. distinguish positive and negative. Positive (subjective) S. name such defects of a field of vision, to-rye the patient in the form of the hull closing a part of the considered subject sees. Positive S.'s presence demonstrates defeat internal «layers of a retina or a vitreous just before a retina. These S. are caused by shielding of light-sensitive elements of a retina patol. the centers located before it. The patient does not notice negative S., they are found only at a research of a field of vision (see. Perimetry , Kampimetriya , Skotometriya ). Usually such S. arise at damage of an optic nerve. At the same time is absent or vision is weakened.

In a form pathological S. can be oval, round, wedge-shaped, the arc-shaped, ring-shaped (annulyarny), etc. E.g., the arc-shaped S. is characteristic hl. obr. for glaucoma, ring-shaped — for a pigmental degeneration of a retina.

On topography distinguish the central, pericentral, paracentral and peripheral Pages. The central scotomas (fig., b) are located in the central part of a field of vision and include a point of fixing. They are observed at damages of a retina in the field of a macula lutea (makulodistrofiya) or at localization patol. process in the field of a papillomakulyarny bunch of an optic nerve (axial neuritis). In the first case of S. happen positive, in the second — negative. Paracentral S. are located in paracentral departments of a field of vision, adjoin from any party a point of fixing. Pericentral S. surround a point of fixing, without being closed with it. A pericenter of l of ny S. Byerrum's scotoma is typical (fig., c). This scotoma dugoobrazno surrounds a point of fixing, is located at distance 10 — 20 ° from a point of fixing and merges with a blind spot. Byerrum's scotoma is a precursory symptom of glaucoma and has a certain predictive value: Byerrum's scotoma can increase at increase in intraocular pressure and decrease or even to disappear at its decrease (functional S.). Two scotomas of Byerrum form ring-shaped S. V of the third stage of glaucoma ring-shaped S. merges with peripheral narrowing of a field of vision. Byerrum's scotoma can be found also at an optic neuritis, thrombosis of the central vein of a retina and other diseases. Peripheral S. are located in peripheral departments of a field of vision. They are characteristic of diseases of an idiovascular cover — chorioretinites (see. Choroiditis ), peripheral departments of a retina — retinites (see the Retinitis), dystrophic processes in peripheral departments of a retina.

The bilateral S. located in of the same name or heteronymic half of a field of vision are named by gemianopichesky S. or hemianopsias (see. Hemianopsia ). At small focal defeats of visual pathways in the field of visual decussation (hiazma) geteronimny (heteronymic) bitemporal are observed, as a rule, binazalny Pages are more rare. At localization small patol. the center above visual decussation (visual tracts, the central part of a visual way, the subcrustal and cortical visual centers) go-monimny (unilateral) paracentral or central gemiano-pichesky Pages develop. These S. arise on the party opposite to localization patol. center.

On intensity (density) of S. divide on absolute and relative. Absolute S. name such defect of a field of vision, in the area to-rogo vision completely is absent, i.e. the test object shown at a research of a field of vision is not visible to investigated. In relative S.'s zone vision is weakened in comparison with the neighboring sites of a field of vision, a white test object, predjyavlyaekhmy at a research of a field of vision, is visible to less light, and color — less saturated. Depending on brightness and the size of a test object C. it can be recognized absolute (at a research by means of less bright or the smaller size of a test object) or relative (during the use of brighter or the bigger size of a test object). Therefore at a research C. it is important to note the size and brightness of a test object. Gradual decrease in intensity of S. towards not changed sites of a field of vision testifies to freshness patol. process and its tendency to progressing. Sharp transition from area C. to a zone of normal vision is characteristic for finished or stabilized patol. process.

Depending on size, intensity and S.'s localization under review apply various methods of their detection, graphic registration and measurement (see. Skotometriya ). It is possible to define S.'s intensity by a research of color sight (color thresholds according to polychromatic tables of Rabkin or on a spektroanomaloskopa).

Pathological S.' identification is important for the correct and early diagnosis of the diseases connected with damage of a retina, optic nerve, visual pathways and the centers. Size discrimination, gives S.'s intensity in dynamics information on the course patol. process and about efficiency of treatment.



Bibliography: Merkulov I. I. Introduction to clinical ophthalmology, page 46, 51, Kharkiv, 1964; The Multivolume guide to eye diseases, under the editorship of V. N. Arkhangelsky, t. 1, book 1, page 493, M., 1962; Cooper R. L., Constable I. Terrell A. Mass screening for glaucoma and other eye diseases using the Arden grating test, Aust. J. Oph-thal., v. 8, p. 131, 1980; Green G. J., Lessell S. Loewenstein J. Ischemic optic neuropathy in chronic papilledema, Arch. Ophthal., v. 98, p. 502, 1980; Harrington D. The visual fields, L., 1964.


Century of H. Marinchev.

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