What is color blindness?
Most of us share a common color vision sensory experience. Some people, however, have a color vision deficiency, which means their perception of colors is different from what most of us see. The most severe forms of these deficiencies are referred to as color blindness. People with color blindness aren’t aware of differences among colors that are obvious to the rest of us. People who don’t have the more severe types of color blindness may not even be aware of their condition unless they’re tested in a clinic or laboratory.
Inherited color blindness is caused by abnormal photopigments. These color-detecting molecules are located in cone-shaped cells within the retina, called cone cells. In humans, several genes are needed for the body to make photopigments, and defects in these genes can lead to color blindness.
There are three main kinds of color blindness, based on photopigment defects in the three different kinds of cones that respond to blue, green, and red light. Red-green color blindness is the most common, followed by blue-yellow color blindness. A complete absence of color vision —total color blindness – is rare.
Sometimes color blindness can be caused by physical or chemical damage to the eye, the optic nerve, or parts of the brain that process color information. Color vision can also decline with age, most often because of cataract - a clouding and yellowing of the eye’s lens.
What are the different types of color blindness?
The most common types of color blindness are inherited. They are the result of defects in the genes that contain the instructions for making the photopigments found in cones. Some defects alter the photopigment’s sensitivity to color, for example, it might be slightly more sensitive to deeper red and less sensitive to green. Other defects can result in the total loss of a photopigment. Depending on the type of defect and the cone that is affected problems can arise with red, green, or blue color vision.
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. Protanomaly is an X-linked disorder estimated to affect 1 percent of males.
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. Protanopia is an X-linked disorder that is estimated to affect 1 percent of males.
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 and is an X-linked disorder affecting 5 percent of males.
Deuteranopia: In males with deuteranopia, there are no working green cone cells. They tend to see reds as brownish-yellow and greens as beige. Deuteranopia is an X-linked disorder that affects about 1 percent of males.
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. It is an autosomal dominant disorder affecting males and females equally.
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 affecting males and females equally.
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. Cone monochromacy is an autosomal recessive disorder.
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. Rod monochromacy is an autosomal recessive disorder.
How is color blindness diagnosed?
Eye care professionals use a variety of tests to diagnose color blindness. These tests can quickly diagnose specific types of color blindness.
The Ishihara Color Test is the most common test for red-green color blindness. The test consists of a series of colored circles, called Ishihara plates, each of which contains a collection of dots in different colors and sizes. Within the circle are dots that form a shape clearly visible to those with normal color vision, but invisible or difficult to see for those with red-green color blindness.
Here are some test you may try
The answer will be given at the end of each test, try to guess the number as much as you can.
Are there treatments for color blindness?
There is no cure for color blindness. However, people with red-green color blindness may be able to use a special set of lenses to help them perceive colors more accurately. These lenses can only be used outdoors under bright lighting conditions. Visual aids have also been developed to help people cope with color blindness. There are iPhone and iPad apps, for example, that help people with color blindness discriminate among colors. Some of these apps allow users to snap a photo and tap it anywhere on the image to see the color of that area. More sophisticated apps allow users to find out both color and shades of color. These kinds of apps can be helpful in selecting ripe fruits such as bananas, or finding complementary colors when picking out clothing.
Be grateful for you can see colors, don't take for granted.