Visual dye

The human visual pigment consists of a glycoprotein called opsin and the so-called 11-cis-retinal, which is a chemical modification of vitamin A1. This is also the reason why vitamin A is so important for visual acuity. Severe deficiency symptoms can lead to night blindness and in extreme cases to blindness.Together with the 11-cis retinal, the opsin produced by the body itself, which exists in different forms for rods and the three cone types (“cone opsins”), is incorporated into the cell membrane. The complex changes with the incidence of light: the 11-cis-retinal changes into the all-trans-retinal and the opsin is also changed. In the rods, for example, metarhodopsin II is formed, which initiates a signaling cascade and transmits the light.

Red-green weakness

Red-green weakness or blindness is a malfunction of color vision that is congenital and inherited X-linked with incomplete penetrance. However, it is also possible that it is a new mutation and therefore neither parent carries this genetic defect. Since men only have one X chromosome, they fall ill much more frequently and up to 10% of the male population is affected.

However, only 0.5% of women are affected, as they can compensate a defective X chromosome with a healthy second one. The red-green deficiency is based on the fact that a genetic mutation for the visual protein opsin has occurred either in its green or red isoform. This alters the wavelength to which the opsin is sensitive and therefore red and green tones cannot be adequately distinguished.

The mutation occurs more frequently in the opsin for green vision. It is also possible that color vision for one of the colors is completely absent, for example if the coding gene is no longer present. A red weakness or blindness is called protanomaly or protanopia (for green: deuteranomaly or deuteranopia). A special form is the blue-cone monochromasia, i.e. only the blue cones and blue vision function; red and green cannot be separated then either.

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