Daltonism

DALTONISM, blindness to red and green colors, first described by the English physicist Dalton, who suffered from this visual defect. The color perception of a normal eye can be characterized as the ability to perceive all colors of the solar spectrum within the range of 800 mμ to 375 mμ in wavelength. Individual rays of specific length (homogeneous rays), as well as all possible color shades found in nature, can be obtained by mixing three spectral colors in various proportions. The normal eye can therefore be considered a trichromatic system. However, there are people with impaired color differentiation abilities. Anomalies of color perception can be divided into the following groups. 1. Weakened trichromatism, in which there is a general decrease in the ability to distinguish colors, and for which such distinction requires more time and a larger area of the colored object. 2. Dichromatic system - partial color blindness to red-green (D. in the proper sense) or yellow-blue components. In D., the spectrum appears divided by a colorless neutral band (499-490 mμ) into two parts. The series of red, orange, and yellow is perceived as a monochromatic yellow area with differences only in the brightness of its individual parts. The maximum of this brightness lies within 600-570 mμ in the yellow part of the spectrum, as in the normal eye; this brightness decreases on both sides, and on both sides of the maximum there should be points of equal brightness, but perceived by the normal eye as red and green colors, while the daltonian perceives them in the same color tone and brightness. This explains why daltonians confuse red and green colors. According to the distribution of brightness in the spectrum, this type of anomaly has 2 subtypes: protanopia, in which the maximum brightness in the left part coincides with 570 mμ (yellow-green), and deuteranopia with a maximum at 600 mμ (orange); in protanopes, the spectrum in the left part is shortened, and the neutral zone lies in the green-blue 490 mμ, while in deuteranopes, the yellow valence extends further to the left, and the neutral zone lies in the green 499 mμ. Thus, protanopia can be characterized as blindness to red and green colors with particularly reduced ability to perceive red, while deuteranopia is blindness to green color.--Other types of dichromatism, as extremely rare cases, include tritanopia - blindness to violet color, and yellow-blue dichromatism. D. represents an anomaly that is inherited. This trait is recessive and is determined by a gene linked to sex, which explains the hereditary transmission of D. through the female (normal) line, with daltonians being predominantly men and only rarely women. According to Helmholtz's theory, the explanation for daltonism should be sought in the loss of function of one of the basic components that perceive red or green color. According to Hering, red-green blindness reduces to the loss of the red-green substance. However, neither theory is able to fully explain this anomaly. Daltonians often do not notice the deficiency in their vision and only when working involving color differentiation do they discover defects in color perception. In cases where the profession is related to color signaling (some types of railway, maritime, and aviation service), daltonians (as first pointed out by Holmgren) may pose a serious public danger, all the more so because red and green are the colors commonly used in signaling. In view of this, most states have introduced the mandatory examination of such personnel for color perception (mainly in transportation). Of all methods for examining all types of color blindness, the most perfect should be considered the mixing of pure spectral colors with the help of Helmholtz's spectroscope and others. For practical purposes, Holmgren's method is most applicable: the subject from a set of colored wool selects all samples close in color to a given color; convenient for the same purpose are Hess's apparatus, Stilling's pseudo-isochromatic charts, Nagel's charts, and other methods. See also Helmholtz, Hering, Vision and Color Perception.