Color blindness is a congenital, rarely acquired pathology of vision, characterized by abnormal color perception. Clinical symptoms depend on the form of the disease. Patients lose the ability to distinguish one or more colors to varying degrees. Diagnosis of color blindness is carried out using the Ishihara test, FALANT test, anomaloscopy and Rabkin polychromatic tables. No specific treatment methods have been developed. Symptomatic therapy is based on the use of glasses with special filters and contact lenses to correct color blindness. An alternative option is the use of special software and cybernetic devices for working with color images.
General information
Color blindness, or color blindness, is a disease in which the perception of color by the retinal receptor apparatus is disrupted while maintaining normal indicators of other functions of the visual organ. The disease was named after the English chemist J. Dalton, who suffered from a hereditary form of this ailment and described it in his works in 1794. Pathology is most common among males (2-8%), occurs only in 0.4% of women. According to statistics, the prevalence of deuteranomaly in men is 6%, protanomaly – 1%, tritanomaly – less than 1%. The rarest form of color blindness is achromatopsia, which occurs with a frequency of 1:35000. It is proved that the risk of its development increases in the case of closely related marriages. A large number of consanguineous couples among the inhabitants of Pingelape Island in Micronesia caused the emergence of a “color-blind society”.
Causes of color blindness
The etiological factor of color blindness is a violation of color perception by the receptors of the central part of the retina. Normally, a person has three types of cones that contain a color-sensitive pigment of a protein nature. Each of the types of receptors is responsible for the perception of a certain color. The content of pigments capable of reacting to all the spectra of green, red and blue ensures normal color vision.
The hereditary form of the disease is caused by a mutation of the X chromosome. This explains the fact that color blindness is more common in men whose mothers are conductors of the pathological gene. Color blindness in women can be observed only if the father has the disease, while the mother is a carrier of a defective gene. With the help of genome mapping, it was possible to establish that mutations in more than 19 different chromosomes can cause the disease, as well as to identify about 56 genes associated with the development of color blindness. Also, color blindness can be caused by congenital pathologies: cone dystrophy, Leber’s amaurosis, retinitis pigmentosa.
The acquired form of the disease is associated with damage to the occipital lobe of the brain that occurs during trauma, benign or malignant neoplasms, stroke, post-comm syndrome, or retinal degeneration, exposure to ultraviolet radiation. Color blindness can be one of the symptoms of age-related macular degeneration, Parkinson’s disease, cataracts or diabetic retinopathy. Temporary loss of the ability to distinguish colors can be caused by poisoning or intoxication.
Symptoms of color blindness
The main symptom of color blindness is the inability to distinguish one color or another. Clinical forms of the disease: protanopia, tritanopia, deuteranopia and achromatopsia. Protanopia is a type of color blindness in which the perception of red shades is disrupted. With tritanopia, patients do not distinguish the blue-violet part of the spectrum. In turn, deuteranopia is characterized by an inability to differentiate green. In the case of a complete lack of color perception ability, we are talking about achromatopsia. Patients with this pathology see everything in black and white shades.
But most often there is a defect in the perception of one of the primary colors, which indicates abnormal trichromacy. Trichromats with protanomal vision need more saturation of red shades in the image to differentiate yellow, deuteranomals – green. In turn, dichromats perceive the lost part of the color gamut with an admixture of preserved spectral shades (protanopes – with green and blue, deuteranopes – with red and blue, tritanopes – with green and red). Red-green blindness is also distinguished. In the development of this form of the disease, a key role is assigned to a genetically linked mutation with sex. Pathological areas of the genome are localized in the X chromosome, so men are more likely to get sick.
Diagnostics
To diagnose color blindness in ophthalmology, the Ishihara color test, the FALANT test, a study using an anomaloscope and Rabkin polychromatic tables are used.
Ishihara’s color test includes a series of photographs. Each of the drawings depicts spots of various colors, which together create a certain pattern, part of which falls out of sight in patients, so they cannot name what exactly is drawn. The test also includes an image of figures – Arabic numerals, simple geometric symbols. The background of the figure of this test differs little from the main background, so patients with color blindness often see only the background, because it is difficult for them to differentiate minor changes in the color scheme. Children who do not distinguish between numbers can be examined with the help of special children’s drawings (square, circle, car). The principle of diagnosing color blindness according to Rabkin tables is similar.
Performing an anomaloscopy and a FALANT test is justified only in special cases (for example, when hiring with special requirements for color vision). With the help of anomaloscopy, it is possible not only to diagnose all types of color perception disorders, but also to study the effect of brightness level, duration of observation, color adaptation, air pressure and composition, noise, age, training on color discrimination and the effects of drugs on the work of the receptor apparatus. The technique is used to establish norms of perception and color discrimination in order to assess professional suitability in certain areas, as well as to control the treatment. The FALANT test is used in the United States to examine candidates for military service. To pass the test at a certain distance, it is necessary to determine the color emitted by the beacon. The glow of the lighthouse is formed by merging three colors, which are somewhat muted by a special filter. Persons suffering from color blindness cannot name the color, but it has been proven that 30% of patients with a mild form of the disease are successfully tested.
Congenital color blindness can be diagnosed at late stages of development, because patients often call colors not as they see them in connection with generally accepted concepts (grass – green, sky – blue, etc.). With a burdened family history, it is necessary to undergo an examination by an ophthalmologist as early as possible. Although the classical form of the disease is not prone to progression, but with secondary color blindness caused by other diseases of the visual organ (cataract, age-related macular degeneration, diabetic neuropathy), there is a tendency to develop myopia and dystrophic lesions of the retina, so immediate treatment of the underlying pathology is required. Color blindness does not affect other characteristics of vision, therefore, a decrease in acuity or narrowing of the visual field in a genetically determined form is not associated with this disease.
Additional studies are indicated in the case of acquired forms of the disease. The main pathology, the symptom of which is color blindness, can lead to a violation of other vision parameters, as well as provoke the development of organic changes in the eyeball. Therefore, patients with acquired form are recommended to perform tonometry, ophthalmoscopy, perimetry, refractometry and biomicroscopy annually.
Treatment of color blindness
Specific methods for the treatment of congenital color blindness have not been developed. Also, color blindness, which has arisen against the background of genetic pathologies (Leber’s amaurosis, cone dystrophy), does not respond to therapy. Symptomatic therapy is based on the use of tinted filters for glasses and contact lenses, which help to reduce the degree of clinical manifestations of the disease. There are 5 types of contact lenses of different colors on the market for color blindness correction. The criterion of their effectiveness is 100% passing of the Ishihara test. Previously, special software and cybernetic devices (ai-borg, cybernetic eyes, GNOME) were developed to help improve orientation in the color palette when working.
In some cases, it is possible to eliminate the symptoms of acquired color vision disorders after the cure of the underlying disease (neurosurgical treatment of brain damage, surgical intervention to eliminate cataracts, etc.).
Prognosis and prevention
The prognosis for color blindness is favorable for life and working capacity, but this pathology worsens the patient’s quality of life. The diagnosis of color blindness limits the choice of profession in those areas where color perception plays an important role (military personnel, commercial transport drivers, doctors). In some countries (Turkey, Romania), it is prohibited to issue a driver’s license to patients with color blindness.
Specific preventive measures to prevent this pathology have not been developed. Non-specific prevention consists in consulting a geneticist of families with closely related marriages when planning pregnancy. Patients with diabetes mellitus and progressive cataracts need to be examined by an ophthalmologist twice a year. During the training of a child with a color perception defect in the lower grades, it is necessary to use special materials (tables, maps) with contrasting colors.
