Daltonism is a specific type of red-green color vision deficiency, also known as color blindness. People with red-green color vision deficiency may confuse colors that contain red or green elements.

The layer of cells at the back of the eye, known as the retina, is responsible for seeing and interpreting light. Two types of light-sensitive cells called photoreceptors enable this: rods — in dim light — and cones, which detect light in brighter environments.

Objects do not automatically possess color. Instead, the eye perceives a certain light frequency that takes on a color’s appearance. Cones are also responsible for identifying different colors. Specifically, they pick up red, blue, and green.

Color vision deficiency occurs when some types of cones are either missing or do not function correctly. This often occurs due to genetics when a person inherits color vision deficiency from a parent with the altered gene.

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Daltonism is a type of color blindness in which people do not have enough cones to distinguish between reds and greens. Cones usually pick up color using the pigments. However, if a person’s cones do not have one or several of these pigments, they may be unable to tell the difference between reds and greens or different shades of these colors.

The condition first got its name from English scientist John Dalton, the first person recorded to have color blindness. His brother also had red-green color blindness, leading Dalton to suggest that color blindness was an inherited condition.

Dichromacy occurs when a person can only see two colors due to only having two working types of cone cells. They cannot see one part of the light spectrum. Different types of dichromacy can develop.

Protanopia involves being unable to see light in the red part of the spectrum. Protanomaly, a less severe form, may make greens seem more dull or less saturated. People with deuteranopia cannot see green light. Some people may have deuteranomaly, a milder form means that some green shades seem more red.

These affect which colors a person may find difficult to distinguish. A person with full protanopia or deuteranopia may not be able to tell the difference between red and green at all.

Color vision deficiency most often passes through a gene connected to the X chromosome. As such, it often passes from a parent assigned female at birth to a child assigned male at birth. Roughly 8% of white males and 0.5% of white females have color vision deficiency from birth, according to the American Optometric Association (AOA).

Several underlying health problems can also damage the retina’s cells and affect color perception. These may include:

Risk factors for developing color blindness might include:

  • being male
  • being an older adult, as color perception reduces with age
  • using medications, including some that help people manage heart disease, high blood pressure, infections, nervous system problems, and psychological disorders
  • exposure to certain toxic chemicals, such as fertilizers or styrene

People with red-green color blindness may see many reds or greens as dull and murky. People with protanopia may confuse the following colors for one another:

  • black with several shades of red
  • darker browns with black and dark shades of green, orange, red, or purple
  • certain blues with specific reds, darker pinks, and purples
  • mid-range greens with some shades of orange

Those with deuteranopia might confuse the following:

  • mid-range reds with mid-range greens
  • blue-green mixtures with grays and mid-range pinks
  • yellows with bright greens
  • light gray or white with lighter pink
  • mid-range red with mid-range brown
  • lilac with light blue

Many with color blindness do not realize they have less varied color perception than others. For example, grass is green, so people with Daltonism may describe the color they see as green, even if this is not how those with a fuller color perception spectrum see grass.

Daltonism color blindness often stays at the same severity if a person has inherited the genes that cause it. If a person acquires it, such as through disease or injury, their symptoms may get better or worse over time, depending on the underlying cause and treatment progress.

The most common way to diagnose color blindness is through a color plate test. An eye doctor — an ophthalmologist — provides a circle consisting of colored dots. Most dots will be different shades of a particular color, but some in the center will form a shape, letter, or number using a contrasting color.

Those with certain types of color vision deficiency, including Daltonism, will find the shape blends with the background. This makes it difficult or impossible to see.

People may not suspect a child has red-green color blindness if the condition does not cause significant disruption or impairment in their daily lives. However, the AOA recommends screening children before they start school, as many teaching materials use color coding to enrich learning.

An eye doctor might also use a hue test for jobs that involve precision with color choice, such as graphic design. During a hue test, individuals have to arrange colors on a spectrum from red to purple. If an individual cannot work out the right order, it may point to color blindness.

Currently, no cure can address hereditary color blindness.

However, certain supportive aids and vision products can help reduce the impact of color blindness, including glasses and contacts that increase the contrast between colors. Apps can also highlight the colors of certain photos if a person takes them on a phone or tablet.

Color blindness due to an underlying health problem or certain medications may get better if a person treats the underlying condition or switches medication. People with an existing condition should speak with a doctor about new color blindness.

Daltonism is a red-green color vision deficiency. It is named after the scientist, John Dalton, who first recorded having these symptoms. It is a form of dichromia, meaning a person only has the use of two of the three types of cone receptors.

People with Daltonism do not have enough functional red-green cone receptors in their retinas to distinguish certain colors. This can lead to murky green colors or difficulties distinguishing reds and green from one another. The color plate test is a useful way to confirm which type of dichromia a person has.