Inherited color vision problems

Most color vision problems are inherited (genetic) problems with the cone cells in the eye that see color. Inherited color vision problems affect both eyes equally, are usually present at birth, and do not change during a person's life.

The most common color vision problems are inherited problems that make it harder to see red or green, so it becomes difficult to distinguish between shades of these two colors. This type of problem affects about 8% of males and less than 1% of females. A rare type of inherited problem that affects the way a person sees blue and yellow shades occurs equally in men and women.1
Types of inherited color vision problems

There are four main types of inherited color vision problems.

The most common type of color vision problem, called anomalous trichromacy, occurs in people who have all three types of cone cells (for seeing red, green, or blue) but are missing or have an abnormal amount of one type of cone cell, or one type has a flaw in the pigments that the cone cells use to sense color.

* People with this type can see all three colors—red, green, and blue—but not as well as people with normal color vision. That is, they see different shades of colors than people with normal color vision.
* The most common color vision problem is trouble seeing red and green. This problem varies greatly from person to person. Some people have only a little trouble seeing red and green, and they may not even know that they have a color vision problem. Other people may have a very hard time seeing red and green.

Another type of color vision problem, called dichromacy, occurs when one of the three types of cone cells is missing. That is, a person can only see two of the three colors.

* Most people with this color vision problem can tell the difference between blues and yellows but have trouble seeing reds and greens. (A very few people in this category can see reds and greens but not blues and yellows.)
* People with this type of problem have more serious color vision problems compared with the first type (anomalous trichromacy).

The third type of inherited color vision problem, called blue-cone monochromacy, occurs when two of the cone cells (red and green) are missing.

* This problem affects only boys and men.
* Distance vision is often poor, and boys with this condition may have shaky eyes (nystagmus).
* A boy or man with blue-cone monochromacy relies only on his blue cones for color vision.

The fourth main type of inherited color vision problem, called achromatopsia, occurs when all three types of cone cells are missing.

* A person with this color vision problem cannot see any color, only shades of gray, black, and white.
* People who have this type of color vision problem may also have other vision problems, such as poor distance and reading vision and sensitivity to light (photophobia).
* This type of color vision problem is the rarest and most severe.
* This is also called rod monochromacy, because the person must rely on the eye's rod cells for vision.

Genetics of inherited color vision problems

Most color vision problems are inherited flaws in the genes that control the production of the cone pigments of the cone cells in the eye that see color.

The genes for the cone cells involved in seeing red and green colors are on the X chromosome. Females have two X chromosomes. Males have only one X chromosome and a Y chromosome, and they receive their X chromosome from their mother.

* A male will have a red/green color vision problem if the flawed gene is on his single X chromosome. A female must have the flawed gene on both X chromosomes to cause color vision problems, and this happens much less often.
* A woman who is carrying a gene for this type of color vision problem has a 50% chance of passing it on to her sons (because they will receive one of her two X chromosomes). Her daughters will have the color vision problem if they receive the flawed gene on the X chromosome from both the mother and the father. This is much less likely to happen.
* A woman may carry the gene for red/green color vision problems without being affected but may pass the gene on to her children. This is why a color vision problem may "skip" a generation in families that have a history of color vision problems.

The genes for the cone pigments involved in seeing blue colors are not on the X chromosome but on a non-sex chromosome that both males and females have. This means blue color vision problems occur equally often in males and females. However, these types of color vision problems are relatively rare.