Color-blindness is the inability to distinguish the differences between certain colors. This condition results from damaged or an absence of color-sensitive pigment in the cone cells of the retina, the nerve layer at the back of the eye.
Most color vision problems are inherited and are present at birth. Approximately 1 out of 12 males and 1 out of 20 women are color blind.
What is Color Blindness?
The human eye sees by light stimulating the retina (a neuro-membrane lining the inside back of the eye). The retina is made up of what are called Rods and Cones. The rods, located in the peripheral retina, give us our night vision, but can not distinguish color. Cones, located in the center of the retina (called the macula), are not much good at night but do let us perceive color during daylight conditions.
The cones, each contain a light sensitive pigment which is sensitive over a range of wavelengths (each visible color is a different wavelength from approximately 400 to 700 nm). Genes contain the coding instructions for these pigments, and if the coding instructions are wrong, then the wrong pigments will be produced, and the cones will be sensitive to different wavelengths of light (resulting in a color deficiency). The colors that we see are completely dependent on the sensitivity ranges of those pigments.
Many people think anyone labeled as "colorblind" only sees black and white - like watching a black and white movie or television. This is a big misconception and not true. It is extremely rare to be totally color blind (monochromasy - complete absence of any color sensation). There are many different types and degrees of colorblindness - more correctly called color vision deficiencies.
People with normal cones and light sensitive pigment (trichromasy) are able to see all the different colors and subtle mixtures of them by using cones sensitive to one of three wavelength of light - red, green, and blue. A mild color deficiency is present when one or more of the three cones light sensitive pigments are not quite right and their peak sensitivity is shifted (anomalous trichromasy - includes protanomaly and deuteranomaly). A more severe color deficiency is present when one or more of the cones light sensitive pigments is really wrong (dichromasy - includes protanopia and deuteranopia).
Different Types of Color Blindness
Normal vision colors are shown on the left hand side of each image.
Protanomaly - Red Weakness
Usually effects one out of 100 males. Protanomaly is referred to as "red-weakness", an apt description of this form of color deficiency. Any redness seen in a color by a normal observer is lot less apparent to those people with this type of color blindness, both in terms of its "coloring power" (saturation, or depth of color) and its brightness. Red, orange, yellow, and yellow-green appear somewhat shifted in hue ("hue" is just another word for "color") towards green, and all appear paler than they do to the normal observer. The redness component that a normal observer sees in a violet or lavender color is so weakened for the protanomalous observer that he may fail to detect it, and therefore sees only the blue component. Hence, to him the color that normals call "violet" may look only like another shade of blue.
Under poor viewing conditions, such as when driving in dazzling sunlight or in rainy or foggy weather, it is easily possible for protanomalous individuals to mistake a blinking red traffic light from a blinking yellow or amber one, or to fail to distinguish a green traffic light from the various "white" lights in store fronts, signs, and street lights that line our streets.
Deuteranomaly - Green Weakness
This effects five out of 100 males. The deuteranomalous person is considered "green weak". Similar to the protanomalous person, they are poor at discriminating small differences in hues in colors such as red, orange, yellow and green region of the spectrum. They will make errors in the naming of hues in this region because they appear somewhat shifted towards red for him. One very important difference between deuteranomalous individuals and protanomalous individuals is deuteranomalous individuals do "not" have the loss of "brightness" problem.
From a practical stand point, many protanomalous and deuteranomalous people breeze through life with very little difficulty doing tasks that require normal color vision. Some may not even be aware that their color perception is in any way different from normal nor do their friends. The only problem they have is passing that "Blank Blank" color vision test.
Protanopia - Red-Blindness
For the protanope, the brightness of red, orange, and yellow is much reduced compared to normal. This dimming can be so pronounced that reds may be confused with black or dark gray, and red traffic lights may appear to be extinguished. They may learn to distinguish reds from yellows and from greens primarily on the basis of their apparent brightness or lightness, not on any perceptible hue difference. Violet, lavender, and purple are indistinguishable from various shades of blue because their reddish components are so dimmed as to be invisible. E.g. Pink flowers, reflecting both red light and blue light, may appear just blue to the protanope.
Deuteranopia - Green Blindness
The deuteranope suffers the same hue discrimination problems as the protanope, but without the abnormal dimming. The names red, orange, yellow, and green really mean very little to them aside from being different names that every one else around them seems to be able to agree on.
Tritanopia – Blue-Yellow Color Blindness
Actually the wording blue-yellow color blindness is misleading. People affected by tritan color blindness confuse blue with green and yellow with violet. So the term blue-green color blindness would be more accurate because the colors blue and yellow are usually not mixed up by tritanopes.
Tritan defects affect the short-wavelength cone (S-cone). There are two different types which can be observed:
Tritanopia: People affected by tritanopia are dichromats. This means the S-cones are completely missing and only long- and medium-wavelength cones are present.
Tritanomaly: This is an alleviated form of blue-yellow color blindness, where the S-cones are present but do have some kind of mutation.
Blue-yellow color blindness can be observed only very rarely. Different studies diverge a lot in the numbers but as a rule of thumb you could say one out of 10’000 persons is affected at most.
Tritan defects can not only be inherited but also acquired during one’s lifetime. In this case it even may be reversible and not permanent like an inherited color blindness. In the case of an acquired defect this is either evolving slowly for example simply through aging or coming instantly caused by a hard hit on your head.
Monochromacy – Complete Color Blindness
This form of complete color blindness is a very rare subtype of color vision deficiency. If you are suffering under monochromacy, you perceive everything just in shades of gray. This makes it really hard to accomplish many everyday tasks, because colors are such a central part of our life. For example, people suffering form monochromacy might mix up the following colors:
green and blue
red and black
yellow and white
Test if Your Color Blind
This is a simple test of Color Blindness. A series of pictures will appear on your screen. We ask you few question based on those pictures. By seeing those pictures you need to answer it. After finishing the test you can find out that you are Color blind or not.
If you weren't able to see some of the numbers in the color test be sure to schedule an eye appointment right away. We offer full comprehensive eye exams and our Calgary Optometrists will take the time and care to ensure your eyes are well looked after. Our team of Optometrists specialize in eye diseases and we'll ensure you get the best care for your eyes.