PERIMETRY (Greek peri around, near + metreo to measure, measure) — a method of a research of a 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) by means of special devices — perimeters. The essence of a method is that field of vision (see) the studied eye is defined in a projection to a concave spherical surface (an arch or a hemisphere), concentric the surfaces of a retina, by presentation to the patient of a test object of given size, brightness and color in various points of an arch (hemisphere) and definition of its provision of rather visual axis of an eye. At P. rough distortion of borders of a field of vision, inevitable is eliminated at its projection to the plane (see. Kampimetriya ).
To the item it is known since the time of Hippocrates (4 century BC). Clinical P.'s founder consider Ya. Purkinye (1825). It for the first time applied an arch to a research of a field of vision and showed a wedge, P.'s value at eye and nevrol. diseases. Aubert and Fer-ster (H. Aubert, R. Forster, 1857) improved Purkinye's technique and developed philosophy clinical the Item. Special development of P. and the equipment for its carrying out received since the beginning of 19 century. Modern methods P. are of great importance for diagnosis and forecasting of a number of diseases of the visual analyzer and a brain.
Items apply at the diseases which are followed by change of borders of a field of vision or focal losses in these borders — scotomas (see. Scotoma ). Glaucoma, pigmental dystrophy of a retina, neuritis and an atrophy of an optic nerve, fibrinferments of the central vein of a retina, and also various damages of a brain belong to such diseases: tumor, arachnoiditis, disturbance of blood circulation.
There are two main ways P.: kinetic P. using a mobile test object and static P. at which a test object is not mobile.
Distinguish the following types of kinetic perimetry: The item with use of a white test object, color, topographical, objective, oftalmoskopichesky P.
Perimetriya with use of a white test object is most widespread in a wedge, practice in the USSR and abroad. The research is conducted serially for each eye (the second eye is closed an easy bandage). Investigated shall be located conveniently at perimeter, having established a chin on a special support of the device so that the studied eye was against the fixating point located in the middle of an arch of perimeter. Looking at a fixating point, investigated shall note the moment when he notices emergence in sight of a moving test object. This provision of a test object on an arch corresponds to a point of a retina where its sensitivity is threshold in relation to a test object, it is noted on the scheme of a field of vision. The movement of a test object needs to be continued to a point of fixing to be convinced of safety of a field of vision throughout all meridian. Turning an arch of perimeter, conduct a research on meridians through 15 °, 30 ° or 45 °. At a research of persons with rather high visual acuity apply a test object to dia. 3 mm. For identification of minor defects and insignificant narrowings of a field of vision of P. carry out by means of a test object to dia. 1 mm.
The color perimetry is carried out similarly P. by means of a white test object, but unlike it apply test objects of blue, red and green colors to dia. 5 or 10 mm; at the same time the moment of the correct distinction investigated colors of the shown object is noted. For an exception of congenital anomaly of color sensation before carrying out color P. it is necessary to investigate patients by means of polychromatic tables E. B. Rabkina (see. Color sight ).
The topographical perimetry (izoptoperimetriya) is carried out by means of several test objects of various size and brightness. As a result of a research receive respectively several isopters — the lines connecting on the scheme of a field of vision of a point, to-rye correspond to points of a retina with identical light sensitivity. This type of P. allows to investigate in details a field of vision and is applied to exact diagnosis of diseases of the visual analyzer. For a research of spatial summation under review use two different-sized objects, to-rye are so straightened with light filters that the amount of light reflected by them becomes identical. It is normal the isopters received at a research by means of these two objects match, at pathology — disperse.
The objective perimetry is based on delimitation of a field of vision by means of a pupillografiya (see. Pupillografiya ), registering pupillary tests investigated, or encephalography (see) way of assessment of alpha rhythms of EEG.
The Oftalmoskopichesky perimetry is carried out by means of the ophtalmoscope (see. Oftalmoskopiya ), registers a rough projection of light to a retina of investigated and it is applied for the purpose of definition of degree of safety of a field of vision and expediency of operational treatment at opacification of optical environments of an eye (e.g., a cataract, a cataract, etc.).
Static (quantitative, quantitative) perimetry
Static (quantitative, quantitative) the perimetry is carried out with use of a motionless test object which is shown investigated in in advance set points of an arch or a hemisphere of perimeter. Brightness of a test object gradually increases from subthreshold to threshold at which it becomes distinguishable the patient. The method is highly informative.
Conditions for carrying out perimetry. Kinetic and static P. are carried out in the conditions of adaptation to various levels of illumination of an arch (adaptoperimetriya): to photopic («day»), scotopic («night») and mezopichesky (intermediate) to levels. Level of illumination influences light sensitivity of photoreceptors of a retina (flasks and sticks). So, at photopic illumination the located hl are most sensitive to light of a flask. obr. in the central area of a retina. The item at this level of illumination allows to reveal defects in the central departments of a field of vision. At scotopic illumination it is the most favorable to investigate peripheral departments of a retina where in these conditions sensitivity of sticks is highest. Practically it is more preferable to P. to carry out at mezopichesky illumination, i.e. in the conditions of simultaneous functioning of sticks and flasks. Color P. needs to be carried out at photopic illumination since in these conditions the coneal device providing color sight is most active.
At P.'s carrying out preparation of investigated is of great importance psikhol. Before P. the patient needs to explain tasks and conditions of a research. Collateral irritants (light, noise) shall be eliminated. It is important for comparison of these P. received by different researchers or in dynamics of a disease that P. was carried out in strictly identical conditions. On the record perimetric chart (fig. 1) the surname, a name, a middle name of the patient, date of a research, the size, brightness and color of a test object, illumination of an arch (hemisphere) of perimeter, width of the pupil investigated shall be noted.
Perimeters — devices for a research of a field of vision which main part is the arch rotating around a horizontal axis or a hemisphere. The arch is painted in gray opaque color, has the radius of 333 mm (in perimeter localizer — 150 mm), on its outer surface are put divisions from 0 ° to 90 ° in both parties from the middle. In the middle of an arch there is a fixating point. The research is conducted by means of test objects: reflecting and self-shining. The reflecting test objects represent the light spot received by means of a special projector, or a mug from paper, enamel (white and color) to dia. 1, 3, 5, 10 mm strengthened on thin cores holders to-rye move manually along an arch. The self-shining test objects are executed in the form of the light sources closed by color or neutral filters or diaphragms.
One of the first perimeters was developed by R. Forster. In the USSR the following models of perimeters are applied: perimeter-loka-lizator of JIB (across Vodovozov), desktop perimeter (Party of Russian Taxpayers-2-01), projective perimeter (PRP-60), and also the spherical perimeters produced abroad.
Perimeter localizer of LV — the portable manual device having an arch and a set of pigmental test objects. By means of this perimeter investigate a field of vision at the patients who are on a bed rest define localization of intraocular foreign bodys or changes on an eyeground (e.g., ruptures of a retina).
The desktop perimeter consists of the basis, an arch with the chart recorder, support for a chin. Borders of a field of vision investigate by means of test objects and note them on the scheme of a field of vision fixed in the chart recorder (fig. 2).
The advantage of the described perimeters is simplicity in the address; a shortcoming — inconstancy of illumination of an arch and test objects, impossibility of control of fixing of the studied eye. Researches by means of these perimeters are indicative.
Considerably the bigger volume of information on a field of vision is obtained by means of projective perimeters in which a light test object is projected on an inner surface of an arch or a hemisphere. A set of the diaphragms and light filters which are built in on the way of a light flow allows is dosed to change the size, brightness and color of objects that gives the chance to carry out not only qualitative, but also quantitative (quantitative) the Item.
The projective perimeter was for the first time offered in 1924 Mr. of Maggiore. In the USSR the projective perimeter — PRP-60 (fig. 3) is applied. In the middle of an arch the self-shining fixating point of red color with a diameter of 1 mm is located. Test objects in the form of a light spot are projected on an arch by means of a projector. Movement of test objects on an arch of perimeter is carried out by turn of the mirror strengthened in the mobile head of a projector given to rotation by a special drum by means of a flexible cable. Borders of a field of vision are applied on the scheme strengthened in the chart recorder. This perimeter is convenient, but heterogeneity of illumination of a visible background does not guarantee adequate accuracy of a research.
The specified defect is eliminated in a design of spherical perimeters. One of types of spherical perimeters — Goldmann's (fig. 4) perimeter represents a concave hemisphere with a radius of 333 mm in which center the support allowing to establish the head investigated so that his eye was in the center of a hemisphere is located. The inner surface of a hemisphere is painted by a white dull paint and is evenly lit with a lamp. Test objects in the form of a light spot receive by means of a projector and a set of replaceable light filters and diaphragms. Movement of test objects is carried out by turn of a mirror of projective system and all projector around vertical axes. Overseeing by position of the studied eye is made through an opening of the fixating point located in top of a hemisphere by means of a special optical tube.
Abroad use the analyzer of a field of vision of Friedman allowing to reveal the most typical defects in the central part of a field of vision. The research is conducted by presentation investigated for a short time (the 100-th shares of sec.) light test objects of a certain brightness in various sites of a field of vision. The quantity and location of the seen test objects allows to judge a field of vision of the patient.
In the most perfect models of modern perimeters achievements of automatic equipment and electronics are used: The COMPUTER, timing and television units that allows to set various programs of a research and automatically to register results.
Bibliography: Marinchev V. N. and Tarutta E. P. Influence of width of a pupil, refraction and accommodation on results of perimetry, in book: Aktualn. vopr, diagn., the wedge and to lay down. glaucomas, under the editorship of A. M. Sazonova, etc., page 43, M., 1979; Mitkokh D. I. and Noskova A. D. Methods and devices of a research of a field of vision, M., 1975; The Multivolume guide to eye diseases, under the editorship of V. N. Arkhangelsky, t. 1, book 2, page 118, etc., M., 1962; Novokhatsky A. S. Clinical perimetry, M., 1973; Der Augenarzt, hrsg. v. K. Velhagen, Bd 2, S. 361 u. a., Lpz., 1972; Harrington D. O. The visual fields, St Louis, 1976; Miles P. W. Testing visual fields by flicker fusion, Arch. Neurol. Psychiat., v. 65, p. 39, 1951; Purkinje J. E. Beobachtungen und Versuche zur Physiologie der Sinne, B., 1825; Tr a qu air H. M. Clinical perimetry, St Louis, 1949.
B. H. Marinchev; A. D. Noskova (tekhn.).