Any inability to see all the colors of the spectrum is known as color blindness. It is estimated that among those of European ancestry an average of 8% of men and 0.5% of females suffer from color blindness.
The extent of color blindness can vary from being unable to distinguish any colors at all, in other words seeing just black and white, as if watching a pre-color early television set, to partial or mild color blindness when difficulty is experienced in distinguishing between red and green.
Causes of Color Blindness
In the large majority of cases color blindness is a result of inherited factors and will be present from birth. Other causes are age related eye problems such as macular degeneration or diabetes and possibly vitamin A deficiency or injury, particularly when very young such as excessive shaking which can cause damage to the brain or retina.
Cone Cells Are Color Receptors
The rear of the eyeball, known as the retina, contains those cells that connect to the brain allowing us to see. There are two types of cell present in the retina.
- Rod cells that allow us to see in low light conditions
- Cone cells that differentiate the various colors in normal light conditions.
In normal vision there are three types of cone cells or receptors, each containing a different pigment that reacts to the various wave lengths present in light. Of the three types of receptor one will react to shorter wave length colors, one to medium wavelengths and the third to long wave colors.
Between the three of them they cover all the various colors and shades of the spectrum. In color blindness one or more of the types of cone cell will be either defective or missing from the retina.
X Chromosome is the Genetic Key
The reason color blindness is so much more prevalent amongst males than females is due to the X chromosome which contains genes that are implicated in color vision. Males have only one X chromosome whereas women have two X chromosomes so the odds that the males, with their only X chromosome being missing or impaired due to an inherited factor, is much greater.
Types of Color Blindness
The most common forms of color blindness are known as
The first is caused by the inability of the cone cells to process shades of the color red which will appear black/light green to those suffering from protonopia.
Around one percent of males have Protonopia. Deuteranopia occurs due to the absence or a defect of the cone cells that distinguish shades of green and red green. Both are caused as a result of hereditary, sex linked factors.
Total color blindness is called monochromacy and is a result of two or all three cone cells being defective or not being present in the retina. Again this is a result of congenital inherited factors.
Job Prospects for the Color Blind
There are other degrees of color blindness ranging from mild to acute, more usually described as partial or total. Depending on the jurisdiction there are a number of occupations that sufferers from color blindness will be barred or will have to take a more detailed eye sight test to gain admittance.
Clearly any task that needs to differentiate between colors will create problems. In some countries a licence to drive motor vehicles is refused even to partial sufferers but fortunately in the west this is rare.
There is no known treatment to cure or alleviate the symptoms of color blindness.