color blindness

Color blindness: description

A person who is able to perceive all colors has three cell types in the retina of his eyes, the so-called cone cells or, in short, cones. The first cell type responds specifically to red light, the second to green, the third to blue light. Experts call color addicts therefore as so-called trichromats, so people who can see three (Greek “tri”) colors (Greek “chroma”).

However, if one, two or even three cone cells do not function, there is a color blindness: the color vision is either limited or one is completely color blind. The defects can be genetic or acquired in the course of life. Typical of the inherent color blindness is that always both eyes are affected. In the acquired color blindness, only one eye can be affected.

Color blindness is one of the color vision disorders of the eye. Depending on the number of defective Zapfenzelltypen the illness is subdivided into three subforms: dichromatics (two functioning cone types), monochromaticity (a functioning cone type) and Achromasie (no functioning cones).

Red-green color blindness

Often, poor eyesight for a particular color, such as red-green vision weakness, is mistaken for true color blindness. But in the red-green visual weakness all three Zapfenzellen work, but one of them is not perfect. If the green cone does not work properly (deuteranomaly), those affected will have difficulty seeing green and distinguishing it from red. If the red cone does not function properly (protanomaly), red is perceived less well and it can hardly be distinguished from green. Both forms are known as red-green eyesight. In the case of blues weakness (tritanomaly), the blue cones work limited, so that the sensation of blue is reduced and it can hardly be distinguished from yellow.

Color vision is limited in all of these forms of color vision, but less so than in color blindness. The color loss of vision is also one of the color vision disorders and is called abnormal trichromatosis.

See – a highly complex process

The process of seeing is a very complex sensory power of the human eye, whereby man is able to distinguish several millions of colors and to see them at dusk. The starting point for this enormous achievement are two different light-sensitive cell types of the retina of the eye: the rod cells, which enable us to enjoy twilight vision, as well as cone cells for the extensive color vision.

The cone cells are located mainly in the Sehgrube, the place for the sharpest vision. Depending on which color and thus wavelength of the light you can perceive, we distinguish:

• Blue cone cells (B-pin or S-cone for “short”, ie short-wave light)
• Green pin cells (G-pin or M-pin for “medium”, ie medium wave light)
• Red cones (R-cones or L-cones for “long”, ie long-wave light)

The light stimuli perceived by the cone and rod cells are transmitted via the optic nerve into the brain. There they are sorted, compared and interpreted, so that we can perceive the respective color. Our brain can distinguish about 200 color tones, about 26 saturation tones, and about 500 brightness levels. This results in several million shades, which the human being can perceive.

Two color theories explain color vision

There are two plausible color theories about color vision. They try to explain how the brain manages to make the entire spectrum of colors perceptible from the three colors red, green and blue.

The Young-Helmholtz theory states that all colors from the three basic colors red, green and blue can be mixed and generated. The so-called counter color theory by Karl Ewald Konstantin Hering (1834-1918) refers to the phenomenon of colored afterimages: if one looks long enough, for example, at a red circle and then at a white surface, then one sees a circle in the opposite color green. In this way the colors and also black and white can be arranged in pairs: red-green, yellow-blue, black-white. In Kries Zone Theory, the two theories are finally summarized.

Farbenblind – Which shapes are there?

The color blindness can be divided into a number of forms, depending on the number and type of non-functioning cone cells.

If one of the three pins does not work, it is called dichromatic vision or dichromatopsia, Affected then are blind to a color. Depending on which pin type is defective, you divide the dichromatopsia entsprechendin:

• Red-blindness, protanopia (colorblind for red); Red pin is broken
• Greenblindness, deuteranopia (colorblind for green); Green pin is broken
• Blue-yellow, tritanopia (colorblind for blue); Blue pin is broken

At the achromatic vision (or Achromasie = Achromatopsia), all three pin types are defective. Affected are completely color blind and can only distinguish about 500 different light-dark levels. Since only the rod cells for twilight vision are present in these color blind people, the disease is also called rod monochromaticity. The Achromasie can be complete or incomplete. In the incomplete form, a remainder of color vision is possible.

People with one Blue Tang monochromasy – Red and green cones are missing – see their world like achromats in light and dark shades, although they still have a certain residual lightness for the color blue. They are missing the red and green cone cells.

Color blindness: symptoms

The color blindness symptoms depend on which and how many of the three cone cells are no longer functioning. It also matters whether color blindness is innate or acquired.

Innate or acquired color blindness?

If the color blindness is genetically determined, it occurs already after birth or in infancy. Concerned persons are always color blind on both eyes and in the further course the symptoms do not improve or worsen themselves. In contrast, acquired color blindness can worsen possible visual disturbances such as lower visual acuity or increased photosensitivity over time.

The differences in the perception of the colors depend on which cell of the retina does not work. So there are those affected with a defective Zapfenzelle (dichromates), some with two defective Zapfenzellen (monochromats) and others even with three no longer functioning Zapfenzellen (Achromats).

Dichromacy: Color blind with a broken pin

Dichromates have either a defective red, green or blue cone, that is, only two of the three cone cells work properly. This form of color blindness can also be acquired. Then both eyes need not be ill, that is, some sufferers are color blind only in one eye.

Redblind (Protanope): Red-blinds lack the cones for the long-wave light range, ie for red. Therefore affected people can distinguish all colors in the red area worse and they confused red and green, red with yellow, brown with green. This form is not to be confused with the red-green weakness.

Greenblind (Deuteranope): Greenblind missing the pin for the medium-wave light range, so the green. Green and red can hardly be distinguished therefore. The problems are similar to those of red-blindness. This form is not to be confused with the red-green weakness.

Blaublind (Tritanope): Blue color blindness is less common than red or green color blindness. Those affected can not see blue and also have difficulty recognizing yellow. In addition, the sufferers suffer from a greatly reduced visual acuity, as the blue cones are much lower on the retina than the blue or red cones.

Monochromaticity: color blindness with two broken pins

Bluegill monochromatism is a rare form of color blindness. Those affected are missing the red and green cones. They only see light-dark shades, although they still have some residual sight for the color blue. They are also sensitive to light, see poorer overall, are mostly short-sighted and have an involuntary tremor (nystagmus) on.

Achromasie: Color blind with three broken cones

In Achromasie none of the three pins works. Those affected can not see any colors at all, they perceive their environment only in light and dark shades. Achromats also look much weaker, are extremely sensitive to light (photophobia) and their eyes can move uncontrollably back and forth (nystagmus).

There is another form of achromatism, the so-called partial achromatism. Affected persons perceive even small remnants of colors and see something sharper overall than people with complete achromatism.

Color blindness: causes and risk factors

Color blindness can either be innate or acquired in the course of life.

Congenital color blindness

The most common color vision disorders are hereditary, that is genetically determined. The disease then occurs after birth in infancy and always affects both eyes. There are a number of genes known which, in the case of a defect, produce the various forms of color blindness.

About eight percent of all men have a congenital color disorder, whereas only about 0.5 percent of women are color blind or color-impaired. The difference is in the genes: Most of the genes responsible for color blindness or color vision weakness are located on chromosome X. Men of this chromosome have only one, but women have two. This means that if a gene on one of the X chromosomes is defective, this can usually be compensated in women by the same gene on the second X chromomeom, if this is normal. The disease, so the color blindness, does not occur then. Women are affected only when the corresponding gene is defective on both X chromosomes.

The Achromasie, that is, the complete color blindness, and the Blauzapfen monochromatics are very rare: Achromasie suffers about one in 30,000 people, in blue-cone monochromatism one of 100,000. The frequency of blue kidney is given as 1: 1,000-65,000. Green blindness occurs in men at about 1.3 percent, in women at about 0.02 percent, red-eye redness in men at 1.0 percent, in women at 0.02 percent.

Acquired color blindness

In contrast to innate color blindness, acquired color blindness can occur on both eyes and only in one eye. It affects men and women equally. Possible triggers are for example:

• Retinal diseases (such as macular degeneration, diabetic retinopathy)
• Diseases of the visual pathway (such as optic nerve inflammation, optic nerve atrophy)
• Diseases of the eyes (like gray or green star)
• stroke

Also, poisoning with drugs (such as sleeping pills) or environmental toxins can cause color blindness.

Color blindness: examinations and diagnosis

Often an innate color blindness is noticed only when family members or friends report about a different color perception. If you suspect colorblind, you should consult your ophthalmologist. First, he will ask you about your health status and possible (pre-) illnesses. He will also ask you questions that will help him narrow down the possible nature of color blindness:

• Is a family member colorblind?
• Does the style of a tomato have the same color as the tomato itself?
• Since when do you feel like you can not distinguish red from green?
• Has your eyesight decreased significantly in the last few months or years?
• Do you still see all colors in one of the two eyes or are both eyes color blind?

Color-blind? Test with the Ishihara tablet

To determine a color blindness, the ophthalmologist uses so-called pseudoisochromatische boards. The world’s most widely used is the Ishihara tablet, named after its Japanese inventor.

Pseudoisochromatic slates are made up of many small circles and show numbers or lines. The background colors and the colors of the figure differ only in hue, but not the brightness and saturation. Therefore, only a healthy color seer can see the figures, not a color blind. With about 38 plates, both eyes or only one eye are examined from a distance of about 75 centimeters. If the figure is not recognized within the first three seconds, the result is “false” or “unsafe”. From the number of false or unsafe answers can then give evidence of a red-green fault.

Ishihara tablets, however, do not help to detect blue-yellow disorders. For this either so-called Velhagen-Stiling-panels are used or certain tests are applied (standard Pseudoisochromatic-Plates-Test, Richmond-HRR-Test, Cambridge-Color-Test).

For children from the age of three, the Color Vision Testing Made Easy test (CVTME test) is suitable. The difference to the mentioned panels lies only in the fact that as figures simple symbols such as circles, stars, squares or dogs are depicted.

Furthermore, there are color reading tests such as the Farnsworth D15 test, in which hats or chips of different colors must be sorted.

Color-blind? Test methods of a different kind

The anomaloscope is an ophthalmological examination device to detect color blindness. The patient must see through a tube on a halved circle. The halves of the circle have different colors. The patient can use turning wheels to try to match the colors and their intensity. A healthy sight can match both hue and intensity, a color blind succeeds only to adjust the intensity.

With the help of the electroretinogram (ERG), ophthalmologists can determine the function of the retina by measuring the electrical activity of the stalk and cone cells.

To determine the innate color blindness with all certainty, genetic tests are used. In this way, mutant genes responsible for the disease can be detected.

Color blindness: treatment

There is currently no therapy for color blindness. Concerning the innate form, scientists are currently increasingly hoping for gene therapy. In animal experiments, some promising results have already been achieved in this area. The researchers therefore hope to be able to carry out gene therapy studies in the near future in humans with congenital color blindness.

Color blindness: disease course and prognosis

The course of the disease of congenital color blindness does not change in the course of life, whereas in the acquired color blindness a deterioration of visual acuity is possible.