Man - one of the few living beings, who was lucky enough to see the world in all the diversity of its colors. But, alas, not everyone sees the surrounding objects the same way. There is a small percentage of people, mostly men, whose perception of colors is somewhat different from the majority. Such people are called colorblind, and if in their life they do not interfere with the peculiarity of their vision (many may not suspect for a long time of rejection), some problems may arise when choosing a procession and passing a medical board. The thing is that the spheres of activity, connected with the risk to the life of others, require correct recognition of colors. We are talking about such professions as a doctor, a motor driver, a machinist, a pilot, a sailor, where one of the elements of professional selection is checking color perception. Problems with the implementation of labor activity can arise in color-blind and in the textile industry, design of landscapes and interiors, work with chemical reagents, etc.
The fact that not all people can see the same object in the same color, scientists began talking in the late eighteenth century, when John Dalton in his writings described the history of his family, in which he and his two brothers had a violation of perception of red. He himself learned about this particular vision already in adulthood. It is worth saying that D. Dalton still discerned colors, but did not see objects in black and white. Just his perception of colors was somewhat different from the traditional one.
Since that time, the pathology of vision, in which a person sees colors differently, has come to be called color-blindness. Many of us are accustomed to consider colorblind people who perceive only black and white tones. This is not entirely correct, because color blindness is a generalized concept, within which there are several groups of people distinguished by color perception.
Man discerns colors due to the special structure of his organ of vision, in the central part of the retina of which there are receptors sensitive to light of a certain wavelength. These receptors are called cones. The eye of a healthy person contains 3 groups of cones with a specific protein pigment, sensitive to red (up to 570 nm), green (up to 544 nm) or blue (up to 443 nm) color.
If a person has in his eyes all 3 kinds of cones in sufficient quantity, then he sees the world as natural, without distorting the available colors. People with normal vision according to scientific terminology are called trichromates. Their vision distinguishes three basic colors and additional colors, formed by mixing the basic shades.
If a person does not have cones of one of the colors (green, blue, red), the image is distorted, and what we see, for example, in blue, he can see red or yellow. These people are called dichromates.
In the environment of dichromates there is already a division into groups, depending on the color of the cones in the eyes of the patients. People with a lack of receptors that are sensitive to green color are called deuteranopes. Those who do not have a blue pigment are called tritans. If in the organs of vision there are no cones with a red pigment, it is a question of protanopia.
So far, it was about the lack of cones of a certain pigment. But a certain part of people have all three types of cones, however, their color perception is somewhat different from the traditional one. The cause of this condition is the deficit of the cones of one of the pigments (they are present, but in insufficient quantity). In this case, we are not talking about Daltonism in the truest sense of the word, but about the abnormal trichromation, in which the perception of colors is weakened. With a deficit of cones in red, they speak of protanomaly, with a lack of blue or green - respectively, about tritanomaly and deuteranomalia.
In the absence of color-sensitive cones, a person can not distinguish colors and sees only different shades of black and white color (achromatopsia). The same picture is formed also in those people whose organ of vision contains cones of only one color (cone monochromasia). In this case, a person can see only shades of green, red or blue colors, depending on the type of cones available. Both groups of people are united by the common name monochromats.
This pathology is rare, nevertheless, it has the most negative impact on a person's life, severely limiting his professional choice. Monochromates have problems not only with choosing a profession, but also with obtaining the rights to drive a car, because they naturally have difficulties with recognizing the signal colors of a traffic light.
Most often there are people with a violation of the color perception of red and green. According to statistics, this pathology is diagnosed in 8 men out of 100. Among women, color blindness is considered a rare occurrence (1 in 200).
To blame people with impaired perception in their pathology is impossible, because in most cases it is congenital (genetic mutation of the X chromosome or changes in the 7 chromosome). True, there is a certain percentage of people whose pathology is considered acquired and affects mainly one eye. Violation of color perception in this case can be temporary or permanent, and it is associated with age-related changes (cloudiness of the lens in the elderly), medication (side effects), and some eye traumas.
Whatever it was, if in everyday life people with anomalies of color perception are more or less smooth, then professionally, everything is not so rosy. It's not for nothing that the medical board when applying for a job in some specialties involves checking the color perception. An identical procedure is also carried out when issuing driving licenses.
If, under anomalous trichromatics, the possibility of obtaining rights does exist, it is true that there is a certain condition - the need to wear corrective colors for lenses or glasses. If a person does not distinguish between red and green colors, then problems begin. But even having obtained the rights to drive a car of category A or B, the color blind man can not professionally engage in the transportation of passengers.
Yes, the laws in this respect vary from country to country. In Europe, for example, there are no such limitations in the issuance of rights, because even monochromat after a certain training is able to remember the location of the colors of the traffic light and adhere to the rules. We have problems with this in our country. And although the laws in this respect are constantly being revised, the drivers have not yet checked the color perception of the drivers. And there is nothing wrong with taking care of safety as a person with a violation of color perception, and the people around him (drivers and pedestrians).
Checking color perception
During the passage of the medical commission when applying for a job (ideally, even at the stage of admission to the educational institution of the corresponding profile), the ophthalmologist's conclusion about the possibility to carry out this or that activity is mandatory. In most cases, it is sufficient to verify visual acuity. However, there are activities that require more careful study of the features of vision, one of which is color perception.
Even for obtaining rights with all possible changes in the composition of medical doctors for other professions, the conclusion of an ophthalmologist still plays a big role.
Checking the color perception is carried out by the oculist in a specially equipped room with good lighting, which does not distort the colors perceived by the eye. Lighting is one of the most important conditions, because it affects the accuracy of the result of the study. According to the annotation to the tables of Rabkin, the room illumination should be at least 200 lux (ideally 300-500 lux). It is better if it is natural light from the window, but you can also use fluorescent lights. Inadequate daylight or conventional artificial light can distort the results of the study, changing the perception of the color gamut of the human eye.
The light source should not be in the field of view of the researcher, dazzling it, or forming glare, if a computer monitor is used to display the tables. It is better to place the light source behind the researched person.
In ophthalmology, there are 3 main methods for testing color sensitivity:
- The spectral method (using a special device - an anomaloscope, equipped with color filters).
- The electrophysiological method, which includes:
- chromatic perimetry (definition of fields of vision for white and other colors),
Electroretinography - computer diagnostics of the disturbance of the work of cones on changes in the biopotential of the retina pr and exposure to it by light rays.
This method is used for suspected ophthalmic pathologies, which can be associated with both eye trauma and some diseases of other body systems.
- Polychromatic method. This method is quite simple and does not require the purchase of special expensive devices. With all this, it gives accurate results. A method is based on the use of polychromatic tables. The most commonly used tables are Rubkin and Justov, less often Ishekhar and Shtilling tests, which are analogous to Rubkin's tables.
Simplicity, cheapness and accuracy of the polychromatic method makes it attractive enough. This method is most often used by ophthalmologists to check the color perception of drivers and people of some other professions, for which such research should be regular.
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Tables for testing color sensations
So, we learned that the most common method for testing color sensitivity is the method of polychromatic tables. The most popular, known since the 30-ies of the twentieth century, are the tables of the Soviet ophthalmologist Efim Borisovich Rabkin.
Their first edition was born in 1936. The last ninth supplemented edition, which ophthalmologists use to this day, was published in 1971. Books for testing the color perception of drivers and representatives of other professions, currently used, contain a set of basic (27 pieces) and control (22 pieces) tables in full size (each figure on a separate page), and a description to them that helps correctly apply the proposed material and make an accurate diagnosis.
The main set of tables is used to diagnose various hereditary types of color perception disorders and differentiate them from acquired pathologies, in which the perception of blue and yellow colors is disrupted. The control set of cards is used if the doctor has doubts about the reliability of the results. It is designed to exclude incorrect diagnosis in the case of exaggeration of symptoms of pathology, simulation of the disease or, conversely, concealment of color perception disorders by memorizing the main tables and deciphering them.
The person during the test is usually seated on a chair with his back to the light source. To place test tables filled with dots of different colors, hues and sizes, against which stand out certain figures, numbers and simple geometric figures, it is necessary at eye level of the researched, with the distance to the used material should be at least 50 cm and not more than a meter.
Demonstration of each of the tables should ideally take about 5 seconds. Reduce the interval is not necessary. In some cases, the exposure time may be slightly increased (for example, when viewing 18 and 21 tables).
If the researched after the study of the table does not give a clear answer, to clarify the result, one can resort to drawing a picture in the picture with a brush. This applies to Tables 5, 6, 8-10, 15, 19, 21, 22, 27.
The criterion for diagnosing trichromasia is the correct reading of all 27 tables. People with a violation of red vision correctly call the figures and figures on 7-8 tables: № 1, 2, 7, 23-26. If you violate the green vision, the correct answers are 9 tables: № 1, 2, 8, 9, 12, 23-26.
Violation of the blue vision is observed mainly in the secondary (acquired) form of pathology. Tables 23-26, which in the given situation will have incorrect answers, make it possible to reveal such an anomaly.
For the category of people with anomalous trichromasia, tables no. 3, 4, 11, 13, 16-22, 27 are of particular importance. For this pathology, the examinees correctly read one or more tables from the list above. And to differentiate the protomanomaly from the deuteronomy, tables No. 7, 9, 11-18, 21 allow.
In the control set of cards, trichomes call figures, figures and colors without errors. Dichromates can correctly name only 10 of the 22 tables: No. 1k, Hk, Un, XIVK, HUK, XVIK, XVIIIK, XIXK, XXK, XXIIK.
The book also has instructions for deciphering the answers and a sample of filling out the study card.
In doubtful cases, sometimes they use the help of threshold tables. Their principle is based on the distinction between the studied point and the minimum saturation of the pigmentation, in which color can still be discerned.
For the study, there are 5 tables with pigment fields 1 cm in size. The colors used are red, green, yellow, blue, gray. 4 chromatic tables contain a scale of 30 fields: from white to the most saturated of a certain color tone, 5 the table contains an achromatic (black and white scale). Special masks with a round hole are attached to the tables, eliminating distortion of colors due to the influence of neighboring fields.
Studies of the thresholds of vision are carried out both with natural and artificial lighting. Each image examined examines 3 times, the final result is an average.
Identically constructed and thresholds Yustovoy table. The set includes 12 cards: No. 1-4 for detecting a red-eye disorder, No. 5-8 for determining deuteranopia (no cones with green pigments), No. 9-11 for identifying those who do not distinguish between blue colors, No. 12-black -a white card for reading the text.
Each card is spread out as a table and has an equal number of cells (6 pieces) vertically and horizontally. 10 cells differ from the others in color and form a sort of square without one side. The task of the researcher is to determine from which side in the square there is a discontinuity.
The larger the card number, the greater the difference between the text color (broken square or letter "P") and cells of the same tone that make up the background. The tables for deuteranopes and protanopes with increasing number have, respectively, 5, 10, 20 and 30 differentiation thresholds. Cards from 9 to 11 for the diagnosis of tritanopia have 5, 10 and 15 differentiation thresholds.
The advantage of the threshold study is the inability to falsify the results, learning the decoding of images on cards, which is practiced in the environment of those who want to get the rights to drive a car, when checking the color perception is carried out using the tables of Rabkin. People simply do not think about the consequences of such falsification in the future.
But the tables Justova has also one significant drawback. Print quality significantly affects the relevance of the results. Incorrect color reproduction during printing led to the fact that some editions of tables Justova gave false results. The use of inkjet printing would significantly reduce the number of deviations, but the price of the finished publication would then be greatly increased, which would be unprofitable from the point of view of mass production.
For the time being, low-cost options are prevalent, performed with the help of lithography, the quality control of which is in great doubt. So useful invention was actually ruined on the vine.