A person who is unable to see or distinguish colors has a dysfunction called color blindness. However, this term is a misnomer. It is rare to be totally color-blind, meaning a person can only see shades of gray. Most persons who have difficulty in discriminating colors or shades of colors, such as reds and greens, are more correctly diagnosed with poor color vision. The majority of persons with decreased color vision inherit this disorder. Men inherit poor color vision more often than women.
In poor color vision, patients have deficits in the neural receptors (specialized proteins) that sense color. These receptors are found on the retina, the photosensitive portion of the eye that lines the posterior (back) part of the globe. The retina has photoreceptors called rods, which are activated in dim light and produce black and white vision, and cones, which are activated in bright light and produce color vision. There are three types of cones that are activated by specific wavelengths of light: red retinal photoreceptors, green retinal photoreceptors, and blue retinal photoreceptors. Therefore, poor color vision is due to a deficit in the cones, particularly in missing only one pigment retinal photoreceptor.
Poor color vision is a genetic disorder that is linked to the X chromosome (the genetic material that helps determine the sex of the organism). This means that the part of the X chromosome that codes for cones has a mutation. Men are more likely to have poor color vision because they only have one X chromosome, while women have two. For a woman to be affected with poor color vision, both of her X chromosomes would have a mutation. In rare cases, a person may not see any color and can only see in shades of gray. This condition is called achromatopsia. Persons with achromatopsia generally have other vision problems including lazy eye, light sensitivity, nystagmus (abnormal, erratic movements of the eye), and poor vision.
Signs, Symptoms, Diagnosis, and Treatment
The most common form of poor color vision is having difficulty in distinguishing between shades of red and green. However, some persons may have difficulty in determining between shades of blue and yellow. Persons with blue-yellow poor color vision may also have difficulty with red-green color vision. If the color vision deficit is mild, people may not realize that they have poor color vision.
Poor color vision is normally detected when a child is learning colors. In general, the child will not be able to tell the difference between reds and greens. A health care professional can test color vision during a routine eye exam and determine the type of poor color vision. Specifically, patients are given a card that has various sized spots or splotches of several shades of red and green or blue and yellow on the paper. One of the colors is used to make the background spots and the other color is in the form of a shape, number, or letter. Patients are then asked what they see. If patients have normal color vision, they will easily be able to see the shape, number, or letter. If they have poor color vision, they will not be able to see a difference between the two colors and see “nothing.” Some persons with a mild form of poor color vision may only have difficulty if the shades of both colors are very similar, meaning both colors are fairly light, instead of one being light in color and the other bright in color. To determine mild poor color vision, the test may only use several shades of reds/oranges/yellows for both the background and shape colors. Readers can test their own color vision at the following link: http://www.colour-blindness.com/colour-blindness-tests/ishihara-colour-test-plates/
There is no known treatment for poor color vision or for achromatopsia as both are genetic disorders. Persons with poor color vision can live normal lives, but may not be able to have certain jobs that depend upon color vision, such as painting, electrical work (to determine the color of the wires), and cooking (to determine the color of cooked meats).
Jennifer L. Hellier
See also: Color Perception; Cones; Nystagmus; Rods; Visual Perception; Visual System
Color Matters. (n.d.). What is color-blindness? Retrieved from http://www.colormatters.com/color-and-vision/what-is-color-blindness. There is a short color blindness test that the reader can use.
Mayo Clinic. (2011). Poor color vision. Retrieved from http://www.mayoclinic.com/health/poor-color-vision/DS00233