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The term “daltonism” is sometimes used to describe red-green colorblindness, although the terms deuteranomaly and deuteranopia are used more commonly today. People with red-green color blindness have impaired vision perception when it comes to red and green. The nature of the impairment can vary considerably, depending on the patient and the number of color-sensitive cones which are missing or not functioning properly.
This condition is named for the first person to write about red-green colorblindness, a British man named John Dalton who published a paper describing his own colorblindness in 1798. It is believed to be the first written discussion of impaired color perception, and led to a spike in interest in researching visual perception and visual impairments. Dalton himself was a noted scientist who accomplished a variety of discoveries during his lifetime, illustrating that being colorblind is not an impediment.
When people first hear the term “colorblind,” they often imagine that this means that people see the world in black and white. In fact, as people will discover if they use a colorblind simulator, true colorblindness, in which the world is perceived in monochromatic tones, is rare. Instead, people with conditions like Daltonism have decreased sensitivity to certain colors which can render some areas of the spectrum difficult to differentiate.
For example, someone with red-green colorblindness may see reds in tones of yellow to brown, depending on the composition of the color. This can become a problem when information is presented visually because certain colors will not stand out against certain backgrounds; for example, red text on a goldenrod background would be difficult to read because the eyes are not sensitive enough to the red to distinguish between the two colors. Likewise, many people with Daltonism have trouble with the purple area of the spectrum, perceiving many purples as blues because of decreased red sensitivity.
Daltonism is a sex linked visual impairment. The gene responsible is found on the X chromosome, which causes the condition to be more common in men than in women. For a woman to experience this visual impairment, she needs to inherit both faulty copies of the gene, while a man needs just one. Women can be carriers, passing the gene on to children who may develop Daltonism themselves or carry the gene into future generations.
Differences in visual perception are often noticed at a young age, especially if a child is taken for regular eye exams. Diagnostic tests to look specifically for problems with color perception can be used if there is a concern that a child has Daltonism or a similar impairment.