A Different Rainbow

We’ve recently added a new protocol to the Smart System: ColorCheck Color Vision Test. Easy to use and completely randomizable, the ColorCheck screening will effectively test for color deficiencies in patients of all ages.

Color blindness isn’t blindness as we know it. It’s more aptly called a color vision deficiency (CVD): the inability or decreased ability to see color, or perceive color differences, under normal lighting conditions. Color blindness affects a significant number of people. Total color blindness is much less common than partial color blindness. There are two major types: those who have difficulty distinguishing between red and green, and those who have difficulty distinguishing between blue and yellow.

In the United States, about 7% of the male population (10.5 million) and 0.4% of the female population (1.2 million) either cannot distinguish red from green, or see red and green differently from how others do. More than 95 percent of all variations in human color vision involve the red and green receptors in male eyes. It is very rare for males or females to be “blind” to the blue end of the spectrum.

Red-Green Color Blindness:

Red-green color blindness affects males much more often than females, because the genes for the red and green color receptors are located on the X chromosome, of which males have only one and females have two. Females (46, XX) are red–green color blind only if both their X chromosomes are defective with a similar deficiency, whereas males (46, XY) are color blind if their single X chromosome is defective.

The gene for red–green color blindness is transmitted from a color blind male to all his daughters who are heterozygote carriers and are usually unaffected. In turn, a carrier woman has a 50% chance of passing on a mutated X chromosome region to each of her male offspring. The sons of an affected male will not inherit the trait from him, since they receive his Y chromosome and not his (defective) X chromosome. Should an affected male have children with a carrier or colorblind woman, their daughters may be colorblind by inheriting an affected X chromosome from each parent.

Blue-Yellow Color Blindness:

Color blindness involving the inactivation of the short-wavelength sensitive cone system (whose absorption spectrum peaks in the bluish-violet) is called tritanopia or, loosely, blue–yellow color blindness. Tritanopia is equally distributed among males and females. The gene coding for the blue receptor is not sex-linked, nor does it have any neighbor whose DNA sequence is similar. Blue color blindness is caused by a simple mutation in this gene.

Inherited color blindness can be congenital, or it can develop later on in childhood or adulthood. Depending on the mutation, it can remain the same throughout a person’s lifetime, or progress.

Other causes of color blindness include accidents and other trauma which produce swelling of the brain in the occipital lobe, damage to the retina caused by exposure to ultraviolet light, and substance toxicity (antibiotics, chemical solvents, etc.).

Color blindness may also present itself in the spectrum of degenerative diseases of the eye, such as age-related macular degeneration, and as part of the retinal damage caused by diabetes. Another factor that may affect color blindness includes a deficiency in Vitamin A.

There are four established tests for determining CVD:

1) Anomalscopes: The anomaloscope provides the most accurate possibility to test the severity of color blindness and distinguish between dichromats and anomalous trichromats. In 1907 the Nagel anomaloscope was introduced and is still known as one of the best. Unfortunately it is not produced anymore.

2) Pseudoisochromatic plates: This is the most famous type of color blindness test. Most people know them under the name Ishihara plates test, because Dr. Shinobu Ishihara was one of the first persons who designed a reliable plate test, introduced in 1917. He produced different test sets. Ishihara plates are still widely used all around the world.

3) Arrangement tests: Such test consists of a certain number of colored discs or plates which have to be arranged in the correct order, starting from a pilot plate. The colors are chosen around the white point and because colorblind people can not distinguish colors along certain lines they will arrange the discs completely different compared to somebody with normal color vision. The most well known test of this type is the Farnsworth D-15 arrangement test, developed in 1947.

4) Lanterns: Specially designed to simulate signals and are therefore most often used as vocational tests. Compared to the other tests with lanterns you are testing the required ability directly. They are robust and have a high practical value. However, they can’t reveal much of the nature and severity of the color vision defect.

FYI:

Paul Newman wanted to be a pilot for the Navy. It was during the flight physical that he discovered he was color blind. So he trained to be a radioman and a gunner and, obviously, went on to become an actor.

Jack Nicklaus “couldn’t tell you a green number from a red on a leader board if the winner’s check depended on it.”

Bing Crosby’s loud clothing was fodder for many jokes back in the day – Bob Hope especially relished zinging Der Bingle for his bad taste. But it’s no wonder that Bing picked out such tacky pieces – he was, quite literally, color blind. “He will think something is a beautiful blue,” his wife once explained, “and it will turn out to be a bilious green.”


Emerson Moser was Crayola’s senior-most crayon maker: after 37 years of employment he had molded more than 1.4 billion crayons. It wasn’t until he retired that he revealed a secret: his blue-green color blindness meant that he couldn’t see all of the colors he was making.

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Courtesy of Wikipedia, and the Colblindor blog

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