Posted by: courtneygrapperhaus | May 12, 2015

Color Blindness – What is it, who gets it, and why?

When I was writing last week’s blog about dog vision, I became curious about color blindness in humans and decided to do some investigating. “Color blindness, or color vision deficiency, is the inability or decreased ability to see color, or perceive color differences, under normal lighting conditions.” (Wikipedia) Before I began researching color blindness, I thought that there were only a couple of types of color blindness. As it turns out, there are several types of color blindness as well as multiple causes.

In 1798 chemist John Dalton wrote “Extraordinary facts relating to the vision of colours”. This paper presented the first scientific findings about color blindness. Dalton decided to write the paper when he realized that he did not see color the same as others. Even though his findings were not well known in his time, his research paved the way for future research on the subject.

Color blindness is most often caused by mutations of he X chromosome and most people are born with it. Other causes are eye disease (such as age-related macular degeneration), drugs, retinal damage, and Vitamin A deficiency. You may recall that our eyes have three types of cones. These cones each contain a different pigment:  blue, green and red. In the most basic terms “color blindness can occur when one or more of the color cone cells are absent, nonfunctioning or detect a different color than normal.” (American Academy of Opthalmology). The National Eye Institute provides the best descriptions about the types of color blindness:

Red-Green Color Blindness

The most common types of hereditary color blindness are due to the loss or limited function of red cone (known as protan) or green cone (deutran) photopigments. This kind of color blindness is commonly referred to as red-green color blindness.

* Protanomaly: In males with protanomaly, the red cone photopigment is abnormal. Red, orange, and yellow appear greener and colors are not as bright. This condition is mild and doesn’t usually interfere with daily living.

* Protanopia: In males with protanopia, there are no working red cone cells. Red appears as black. Certain shades of orange, yellow, and green all appear as yellow.

* Deuteranomaly: In males with deuteranomaly, the green cone photopigment is abnormal. Yellow and green appear redder and it is difficult to tell violet from blue. This condition is mild and doesn’t interfere with daily living. Deuteranomaly is the most common form of color blindness.

* Deuteranopia: In males with deuteranopia, there are no working green cone cells. They tend to see reds as brownish-yellow and greens as beige.

Blue-Yellow Color Blindness

Blue-yellow color blindness is rarer than red-green color blindness. Blue-cone (tritan) photopigments are either missing or have limited function.

* Tritanomaly: People with tritanomaly have functionally limited blue cone cells. Blue appears greener and it can be difficult to tell yellow and red from pink. Tritanomaly is extremely rare.

* Tritanopia: People with tritanopia, also known as blue-yellow color blindness, lack blue cone cells. Blue appears green and yellow appears violet or light grey. Tritanopia is an extremely rare autosomal recessive disorder.

Complete color blindness

People with complete color blindness (monochromacy) don’t experience color at all and the clearness of their vision (visual acuity) may also be affected.

There are two types of monochromacy:

* Cone monochromacy: This rare form of color blindness results from a failure of two of the three cone cell photopigments to work. There is red cone monochromacy, green cone monochromacy, and blue cone monochromacy. People with cone monochromacy have trouble distinguishing colors because the brain needs to compare the signals from different types of cones in order to see color. When only one type of cone works, this comparison isn’t possible. People with blue cone monochromacy, may also have reduced visual acuity, near-sightedness, and uncontrollable eye movements, a condition known as nystagmus.

* Rod monochromacy or achromatopsia: This type of monochromacy is rare and is the most severe form of color blindness. It is present at birth. None of the cone cells have functional photopigments. Lacking all cone vision, people with rod monochromacy see the world in black, white, and gray. And since rods respond to dim light, people with rod monochromacy tend to be photophobic – very uncomfortable in bright environments. They also experience nystagmus.

Optometrists and opthalmologists use several tests to diagnose color blindness. The most common of these is the Ishihara Color Test. This test involves the patient looking at special circles with dots in varying colors and sizes and identifying the shape those dots create. Other tests include the Cambridge Color Test, an anomaloscope, the HRR Pseudoisochromatic Color Test, the Farnsworth-Munsell 100 Hue Test, and the Farnsworth Lantern Test (used by the US Military).

Color Blindness Types - ishihara

While there is no cure for congenital color blindness, most people learn to adapt. Some individuals choose to manage via special glasses, contact lenses, and apps for smart phones. Today, scientists are developing new methods to assist color blind people see colors. A group of researchers recently tried using gene therapy in adult male squirrel monkeys, who are all red-green color blind. The gene therapy seemed to work but translating this into use on humans will take some time.


Past Blogs about color blindness

What’s the difference between red / green color blindness and total color blindness and why is testing so important?

Online color vision tests – do they really work?

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