Dichromasia

If a person distinguishes only two primary colors, then this condition is called dichromasia. Let's consider the causes of this pathology, types, diagnostic methods, and treatment.

Color vision disorders are serious anomalies that can be both congenital and acquired. Hereditary mutations and other pathological processes in the organs of the optical system lead to functional disorders of the cone system. The disease is transmitted only by a recessive type. It is diagnosed in 8% of men and 0.4% of women. At the same time, it is women who are asymptomatic carriers of the mutant gene.

Basic qualities of color:

• Tone is a characteristic of color and depends on the length of the light wave.
• Saturation – is determined by the proportion of the main tone with admixtures of another color.
• Brightness (lightness) is the degree of dilution with white.

With normal perception, a person distinguishes many shades of all primary colors. Ophthalmologists call this condition normal trichromacy. If there are certain disorders with the recognition of color spectrum waves, the patient may be diagnosed with the following conditions: protan defect (pathology of red), tritan defect (blue color) and deuter defect (green color). Problems with the recognition of any primary color, usually green, less often red, are distinguished by the degree of disorder: anomalous trichromacy, dichromacy, monochromacy.

If a person perceives two primary colors, then this is dichromacy. This condition was first described by a scientist and physician - Dalton, after whom the most common anomaly is named - color blindness. With complete color blindness, the world is perceived in black and white shades, and the pathology is called monochromacy. Severe disorders of all pigment layers are extremely rare. Dichromacy is detected more often, its diagnosis is carried out using special ophthalmological testing.

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Epidemiology

Medical statistics indicate that dichromacy is more common in men than in women. The disease is associated with damage to the central part of the retina, where nerve cells containing three types of color-sensitive pigments of protein origin are located. Each pigment perceives a certain color: red, blue, green. Their mixing ensures normal recognition of colors.

According to statistics, problems with the red pigment are diagnosed most often. At the same time, 8% of men and about 0.4% of women have a red-green defect of color vision. In 75% of patients, recognition of only one color is significantly reduced. Complete color blindness is extremely rare and, as a rule, occurs with other anomalies of the organs of the optical system.

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Causes dichromasias

The main causes of dichromacy, i.e. the inability to adequately recognize colors, are the disruption of the color-sensitive receptors. They are located in the central part of the retina and are special nerve cells - cones. There are three types of cones, which have the following characteristics of perception of the primary color:

• 1 pigment – captures the green spectrum with a length of 530 nm.
• 2 pigment – recognizes red with a wavelength of 552-557 nm.
• 3 pigment – blue spectrum with a length of 426 nm.

If all three pigments are present in the cones, then this condition is normal and is called trichromacy. The causes of visual anomalies can be congenital or acquired:

1. The hereditary factor is a mutation of the female X chromosome. That is, the disease is transmitted from the carrier mother to her son. It is in men that this pathology manifests itself more often, since they do not have an additional X chromosome in the gene set that could eliminate the mutation. According to statistics, the disorder occurs in 5-8% of men and 0.4% of women.
2. Acquired form – not associated with the transmission of a mutant gene. Occurs with dystrophic or inflammatory lesions of the retina. The disorder can develop with optic nerve atrophy, brain diseases, various skull and eye injuries, medication use, or age-related pathologies.

This type of disorder most often manifests itself in only one eye. Over time, the pathology becomes more pronounced. Against its background, optical media transparency disorders may develop, that is, pathologies of the macular region of the retina. A decrease in visual acuity and visual field impairment are also possible.

Knowing the causes of the pathological condition significantly simplifies the process of diagnosis and correction of visual anomalies.

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Risk factors

Inability to adequately recognize color has certain risk factors that increase the chance of developing pathology. Let's consider them:

• Genetic predisposition. If there is a family history of color blindness, then the probability of inheriting the pathology increases.
• Male gender – men suffer from color blindness more often than women.
• Some medications can damage the optic nerves and retina.
• Age-related degenerative changes (clouding of the lens, cataracts).
• Retinal trauma with damage to the macula.
• Leber optic neuropathy is a genetic disorder that causes damage to the optic nerves.
• Parkinson's disease - due to a disorder in the conduction of nerve impulses, the correct formation of a visual image is disrupted.
• Brain damage (occipital lobe) caused by trauma, stroke or tumors.

During the examination, the ophthalmologist takes into account the above-mentioned risk factors, which simplifies the final diagnosis.

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Pathogenesis

Dichromacy is associated with a disorder in recognizing the waves of the color spectrum. The pathogenesis of the congenital anomaly is based on the absence of one or more color-sensitive receptors in the central part of the retina. In the acquired form, the receptors, i.e. cones, are affected.

The following differences are distinguished between the development mechanism of congenital and acquired diseases:

• Congenital pathology is characterized by decreased sensitivity only to red or green color. Acquired - to red, green and blue.
• In acquired disorders, contrast sensitivity is reduced; in hereditary disorders, it is not reduced.
• The genetic form is stable, while the acquired form can vary in type and degree.
• The level of functionality in the hereditary form is reduced but stable; in the second case, changes are possible.

In addition to the above differences, the genetic disorder is binocular and more common in men, the acquired form can be either monocular or binocular, affecting both men and women equally.

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Symptoms dichromasias

With normal color perception, all primary colors are distinguished. Symptoms of dichromacy are manifested by the loss of one of the three pigments from color vision: green, red or blue. That is, the patient perceives only two primary colors.

If the disease is caused by genetic factors, it manifests itself with the following anomalies:

• Protan defect - red color.
• Tritan defect - blue color.
• Deiter defect - green color.

Patients with dichromacy perceive the lost part of the color spectrum with the help of an admixture of preserved spectral shades:

• Protanopes are green and blue.
• Tritanopes - green and red.
• Deuteranopes - red and blue.

There is also red-green blindness. The development of this form of the disease is largely associated with a genetically linked sex-linked mutation. Most often, its symptoms appear in men.

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First signs

The manifestations of dichromacy are individual for each individual case. The first signs largely depend on the cause of the disease. Most often, mild disorders of color perception occur:

• Red-green perception disorder.
• Problems recognizing blue and green.
• Low visual acuity.
• Nystagmus.

In particularly severe cases, the disease manifests itself as a grey perception of all colours.

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Dichromacy, protanopia

One of the common problems with color perception (recognizing only two pigments) is dichromacy. Protanopia is a type of it. This form of the disease is characterized by the inability to distinguish red. The disorder is based on the absence of the photosensitive pigment erythrolabe in the cones of the retina.

With protanopia, the patient perceives light green (yellow-green) as orange (yellow-red), cannot distinguish blue from purple, but distinguishes blue from green, and green from dark red.

Today, the pathology is incurable, but protanopia does not affect the quality of life. To correct the disorder, special lenses or glasses are used, glass that blocks bright colors from getting into the eyes. Some patients are helped by wearing dark glasses, since dim light helps activate the cones.

Stages

The following degrees of dichromacy are distinguished:

• Slight reduction in color perception.
• A deeper disorder.
• Loss of pigment perception (usually green or red).

The non-perception of one of the primary colors significantly changes the perception of others. Based on this, it is very important to diagnose the pathology and determine its degree. This is especially relevant for people whose work requires full color discrimination (medical workers, pilots, drivers, military personnel, workers in the chemical industry and radio engineering specialties, people working with mechanisms).

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Forms

Dichromacy is a moderate visual disorder. It is based on the malfunction of one of the three receptors. The disease occurs when a certain pigment is damaged and color recognition occurs only in two planes.

Types of pathological conditions:

• Protanopia – light with a wavelength of 400 to 650 nm is not perceived instead of the usual 700 nm. There is a complete loss of red, that is, dysfunction of its photoreceptors. The patient does not see scarlet colors, perceiving them as black. Violet is not distinguished from blue, and orange is presented as dark yellow. At the same time, all shades of green, orange and yellow, the length of which is great for stimulating blue receptors, are presented in a yellow tone.
• Deuteranopia is the loss of photoreceptors of the second type. The patient does not distinguish between green and red.
• Tritanopia is an extremely rare disorder with a complete absence of blue pigment. The disease is associated with the seventh chromosome. Blue looks green, purple - dark red, orange - pink.

The method of correction and the general prognosis for the patient depend on the type of visual anomaly and its severity.

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Complications and consequences

As a rule, dichromacy caused by hereditary factors does not cause health problems. Various consequences and complications are possible if the disease has an acquired form. That is, when the disorder is associated with other pathologies, for example, trauma to the retina or brain, tumor neoplasms.

The patient is prescribed correction of vision features and complex treatment of the complications caused. Recovery in this case depends on the severity of the pathological consequences.

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Diagnostics dichromasias

To determine the level of color perception in a patient, a set of various studies is indicated. Diagnosis of dichromacy is carried out using the following methods:

• Pigment methods

The doctor uses special polychromatic, i.e. multi-colored tables. They are filled with multi-colored circles of the same brightness. In the center of each table there are numbers or geometric figures of different shades, which the patient must name. The ophthalmologist records the number of correct answers, marking the color zone. Based on the results of the study, the degree and type of visual pathology are determined. If the patient cannot distinguish obvious signs, but easily names hidden ones, then he is diagnosed with a congenital visual anomaly.

• Spectral methods.

Diagnostics are carried out using special devices. This may be Rabkin's spectroanamaloscope, Girenberg and Ebney's devices, or Nagel's anomaloscope. The anomaloscope is a device that doses out color mixtures, achieving subjective equality of colors. The device is used to detect disorders in the red-green range. With its help, it is possible to diagnose not only dichromacy, but also its degree and types, i.e. deuteranopia or protanopia.

In most cases, the above methods allow diagnosing a visual anomaly, regardless of the nature of its origin. There are also methods that allow detecting the disorder during intrauterine development. Such diagnostics are carried out if there are cases of visual anomalies in the family. The pregnant woman is prescribed a special DNA test that determines the color blindness gene.

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Dichromacy test

Diagnosis of color vision problems consists of various tests. The dichromacy test is most often performed using Rabkin polychromatic tables or their analogue Ishihara tables.

During the test, the patient is shown tables with various images, these can be figures, numbers or chains. The image consists of many small circles with the same brightness. The main set for testing consists of 27 color tables. If there is a need to clarify the diagnosis, then all 48 tables are used.

If a person does not distinguish colors during the test, then the table looks uniform to him. People with normal vision distinguish pictures. To conduct the test, you must follow these rules:

• The test should take place in a room with natural light, and the patient should sit with his back to the window.
• It is important to ensure that the subject is completely calm and relaxed.
• Each picture should be shown at eye level and at a distance of about 1 m. The viewing time should be within 5-7 seconds.

If the dichromacy test is performed at home on a personal computer and the patient does not distinguish all the colors, then this is not a reason to be upset. Since the test result largely depends on the color and resolution of the monitor. Only an ophthalmologist should perform diagnostics.

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Tables for determining dichromacy

Diagnostic tables for determining dichromacy, i.e. the level of color perception, allow to establish the degree of disorder and its form. Most often, Rabkin tables are used, which consist of two groups:

• Basic – 27 tables for differentiating the forms and degrees of the disorder.
• Control – 20 tables to clarify the diagnosis in case of simulation, aggravation or dissimulation.

Diagnostic tables are developed on the principle of equalizing circles of different colors by saturation and brightness. They indicate numbers and geometric figures that are perceived by color anomalies. At the same time, symbols highlighted in one color that the patient does not perceive are skipped.

To obtain reliable results, it is very important to follow all testing rules. The patient should sit with his back to the window or light source. The tables are shown in a strictly vertical plane at the eye level of the subject. The time for studying one image should not exceed 5-7 seconds. It is not recommended to put the diagnostic tables on the table or hold them at an angle, as this negatively affects the accuracy of the method and its results.

The answers obtained as a result of the test are recorded in a special card. A normal trichromat will read all the tables, an abnormal one - more than 12, and a person with dichromacy - 7-9. Disorders are assessed on the scale of color weakness. In addition to Rabkin's tables, Yustova's tables are used in clinical practice to determine the thresholds of color discrimination, that is, the color strength of the visual apparatus. Such complex diagnostics allows you to catch the most minimal differences in the tones of two colors that occupy close positions in the color range.

Differential diagnosis

Color vision disorders have different forms, types and degrees of severity. Differential diagnostics of dichromasia allows to separate it from other dysfunctions of photoreceptors.

Differentiation is carried out using polychromatic tables. A patient with color blindness will see all images as uniform, a trichromat will distinguish images, and a dichromat will identify only some of the proposed pictures.

Based on the results of the studies, a treatment plan is drawn up. Correction is carried out using special lenses. If the disease is caused by a gene mutation during intrauterine development, then using genetic engineering, missing genes can be introduced into the retina of the eye, which restore normal color recognition.

What is the difference between dichromacy and color weakness?

Functional pathologies of the cone system have several types and forms, which largely depend on the cause of the disorder. Many patients who have encountered a problem with color perception ask themselves the question: what is the difference between dichromacy and color weakness?

• Dichromasia is a color vision disorder caused by congenital or acquired factors. It is characterized by the absence of the function of one of the three color-sensing apparatuses. The lost color is compensated by mixing shades of others.

• Color weakness is the inability to distinguish individual shades of colors, but not the colors themselves. That is, the palette is slightly distorted, but present. In most cases, this does not cause problems and is only detected during comprehensive ophthalmological testing.

Normal color perception is trichromacy. Congenital defects of the organs of the optical system are divided into: defect of perception of red, green or blue color. Dichromacy is characterized by complete blindness to one color, and with monochromacy the patient has black and white perception.

Treatment dichromasias

Dysfunction of photoreceptors can be associated with both congenital and acquired factors. Treatment of hereditary dichromasia, i.e. caused by gene mutation during intrauterine development, is practically not carried out. Only in particularly severe cases, as a rule, with complete color blindness, the missing genes are introduced into the affected retina using genetic engineering.

In case of treatment of acquired dichromasia, positive results are possible. Let's consider the main treatment options:

1. Surgical treatment is used in the development of ophthalmological damage associated with clouding of the lens of the eye. The operation is performed for glaucoma, cataracts, retinopathy and other diseases. But if the disorders are associated with the aging process and natural clouding of the lens of the eye, then such changes are irreversible.
2. Compensation for color vision problems:
   • Glasses with a bright color blocking function are prescribed for people whose color vision problems are caused by bright colors that prevent them from recognizing other colors.
   • Corrective lenses for special purposes - similar in principle to glasses, but can slightly distort objects.
   • Glasses with tinted or dark lenses are recommended for complete color blindness. Their therapeutic effect is explained by the fact that in dim light the cones of the eyes work better.
3. Stopping or discontinuing medications that caused the inability to adequately recognize color. The disorder is possible with a severe deficiency of vitamin A or after taking Chlorquine. In the latter case, visible objects are colored green. If high bilirubinemia is diagnosed, objects are colored yellow.

Timely diagnosis and treatment of the pathological condition at early stages allows us to minimize the risk of photoreceptor dysfunction.

Prevention

There are no specific measures to prevent dichromasia. Prevention consists of consulting a geneticist when planning a pregnancy. This allows identifying hereditary factors that increase the risk of developing the anomaly.

It is necessary to observe safety precautions and wear protective glasses when working with hazardous substances. Since eye injuries are considered risk factors for the disease.

People with diabetes or advanced cataracts should undergo comprehensive diagnostics by an ophthalmologist twice a year. When teaching pediatric patients with color vision deficiencies, it is recommended to use educational materials with contrasting colors.

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Forecast

In general, dichromasia has a positive prognosis for life and ability to work. But the peculiarities of vision can worsen the patient's quality of life.

The disorder prohibits the choice of profession in those areas where the difference in colors is important. If the disease is caused by injuries or other diseases, the prognosis depends entirely on the possibility and effectiveness of their treatment.

Dichromacy and Driver's Licenses

People with vision problems have limitations in certain areas of life. To obtain a driver's license, in addition to the ability to drive a car and knowledge of traffic rules, it is necessary to provide a medical certificate. A medical commission determines whether a person is fit to drive a vehicle.

There is a list of diseases for which a driver's license is not issued. First of all, it is the quality of vision. If a decrease in visual acuity is diagnosed, then its correction is required for driving. Particular attention is paid to the color perception of the eye. This characteristic is very important, since if it is violated, the driver will not be able to recognize the colors of the traffic light. In case of retinal detachment or glaucoma, driving is prohibited.

Dichromacy and other forms of color vision impairment are grounds for refusal to issue a driving license. That is, dichromacy and a driving license are incompatible. But if the photoreceptor dysfunction can be corrected, there is a chance to get a license.

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