colour blindness

50 Facts about Color Blindness

 January 6, 2009Academic

#01 99% of all colorblind people are not really color blind but color deficient; the term color blindness is misleading.

#02 Red-green color blindness is a combination of red-blindness (protan defects) and green-blindness (deutan defects).

#03 Color blindness is more prevalent among males than females, because the most common form of color vision deficiency is encoded on the X sex chromosome.

#04 “What color is this?” is the most annoying question you can ask your colorblind friend.

#05 There are three main types of color vision deficiency: protan, deutan, and tritan defects.

#06 Strongly colorblind people might only be able to tell about 20 hues apart from each other, with normal color vision this number raises to more than 100 different hues.

#07 Colored lenses or glasses can improve color discrimination in your problem areas but can not give you back normal color vision.

#08 Ishihara plates are the best known color blindness tests, but they are not the most accurate ones.

#09 About 8% of all men are suffering from color blindness.

#10 Severity of color blindness is usually divided into the following four categories: slightly, moderate, strong, and absolute.

#11 The terms protan, deutan, and tritan are Greek and translate to first, second, and third.

#12 A father can’t pass his red-green color blindness on to his sons.

#13 Dogs are not colorblind.

#14 Color vision deficiency would be a much better term; but it is not as easy to pronounce compared to color blindness.

#15 There are people which are really suffering from complete color blindness, which is called achromatopsia or monochromacy.

#16 Blue-yellow color blindness would be better called blue-green color blindness, as this are more the problemcolors.

#17 There exists every nuance of color vision deficiency severity, starting from almost normal color vision up tocomplete color blindness.

#18 Protanopia, deuteranopia, and tritanopia are types of dichromacy, which means you have only two different color receptors (cones) compared to three with normal color vision.

#19 If a woman is red-green colorblind, all her sons will also be colorblind.

#20 Colorblind people feel handicapped in everyday life, and almost nobody recognizes this.

#21 99% of all colorblind people are suffering from red-green color blindness.

#22 When using color correcting lenses you are wearing two differently colored lenses in your eyes.

#23 Red-green color blindness is a recessive sex linked trait, which causes more men to be colorblind than women.

#24 John Dalton wrote the first known scientific paper regarding color blindness.

#25 Protanomaly, deuteranomaly, and tritanomaly are types of anomalous trichromacy, which means you have three different color receptors (cones) like people with normal color vision but one of them is shifted in its peak.

#26 In certain countries you need normal color vision to get a drivers license.

#27 Deuteranomaly—one form of red-green color blindness—is by far the most common form of color blindness.

#28 More women than men are carriers of color blindness, even though they are not colorblind themselves.

#29 Some people get rejected from a job assignment because of their color vision deficiency.

#30 About 0.5% of all women are suffering from color blindness.

#31 Blue-yellow color blindness is a dominant not sex linked trait, which means both men and women are equally affected.

#32 Red-green color blindness doesn’t mean that you are only mixing up red and green colors, but the whole color spectrum can cause you problems.

#33 The anomaloscope is the most accurate color blindness test known today.

#34 Police officer, firefighter, and airline pilot are the most famous jobs which require normal color vision.

#35 There is no treatment or cure for color blindness.

#36 Pseudoisochromatic plates were introduced by Professor J. Stilling of Strassburg in 1883; the Ishihara plates by Dr. Shinobu Ishihara followed almost half a century later.

#37 Different chromosomes are involved as sources for the different types of color vision deficiency.

#38 Women can also suffer from color vision deficiency.

#39 Monochromacy—also called achromatopsia—means you have only one type of color receptors (cones) in your eyes.

#40 Color blindness is also called Daltonism, after the scientist John Dalton.

#41 The most often used types of color blindness tests are: pseudoisochromatic plates, arrangement test, and theanomaloscope.

#42 Better color vision deficiency terms would be: red-blindness for protanopia, red-weakness for protanomaly, green-blindness for deuteranopia, green-weakness for deuteranomaly, blue-blindness for tritanopia, and blue-weakness for tritanomaly.

#43 John Dalton believed his whole life that the cause of his color blindness is a colored fluid inside his eye balls.

#44 Many colorblind people have problems with matching clothes and buying ripe bananas.

#45 Quite a lot of people with normal color vision can’t pass an Ishihara plates test free of errors.

#46 The International Colour Vision Society is scientifically investigating every aspect of color vision and color vision deficiency.

#47 Confusion lines of the CIE 1931 color space show exactly the colors of confusion for all forms of color blindness.

#48 Only a whole battery of color blindness tests can reveal the true type and severity of your color vision deficiency.

#49 John Dalton was also colorblind himself.

#50 A Colblindor is a colorblind person who learned to enjoy his colorblind life ;-)

http://www.color-blindness.com/2009/01/06/50-facts-about-color-blindness/

Types of Colour Blindness

There are several types of inherited colour blindness. For information on acquired colour vision defects refer to our page Acquired Colour Vision Defects

Trichromacy

Normal colour vision uses all three types of light cones correctly and is known as trichromacy. People with normal colour vision are known as trichromats.

Anomalous Trichromacy

People with ‘faulty’ trichromatic vision will be colour blind to some extent and are known as anomalous trichromats. In people with this condition all of their three cone types are used to perceive light colours but one type of cone perceives light slightly out of alignment, so that there are three different types of effect produced depending upon which cone type is ‘faulty’.

Normal Vision

Deuteranomaly

The different anomalous conditions are protanomaly, which is a reduced sensitivity to red light, deuteranomaly which is a reduced sensitivity to green light and is the most common form of colour blindness and tritanomaly which is a reduced sensitivity to blue light and is extremely rare.

The effects of anomalous trichromatic vision can range from almost normal colour perception to almost total absence of perception of the ‘faulty’ colour.

People with deuteranomaly and protanomaly are collectively known as red-green colour blind and they generally have difficulty distinguishing between reds, greens, browns and oranges. They also commonly confuse different types of blue and purple hues.

People with reduced blue sensitivity have difficulty identifying differences between blue and yellow, violet and red and blue and green. To these people the world appears as generally red, pink, black, white, grey and turquoise.

See the dichromacy images below – about half of people with anomalous trichromacy will see the world in a similar way to those with dichromacy but their ability to perceive colours will improve in good light and deteriorate in poor light. Often their colour perception can be as poor as it is for those with dichromacy.

People with anomalous dichromacy can have either inherited colour blindness, in which case their ability to see colours will remain the same, or they can have acquired it, in which case their condition could get worse, or possibly improve over time

Dichromacy

PROTANOPIA

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People with dichromatic colour vision have only two types of cones which are able to perceive colour i.e. they have a total absence of function of one cone type. Lack of ability to see colour is the easiest way to explain this condition but in actual fact it is a specific section of the light spectrum which can’t be perceived. For convenience we call these areas of the light spectrum ‘red’, ‘green’ or ‘blue’ . The sections of the light spectrum which the ‘red’ and ‘green’ cones perceive overlap and this is why red and green colour vision deficiencies are often known as red/green colour blindness and why people with red and green deficiencies see the world in a similar way.

People suffering from protanopia are unable to perceive any ‘red’ light, those with deuteranopia are unable to perceive ‘green’ light and those with tritanopia are unable to perceive ‘blue’ light.

People with both red and green deficiencies live in a world of murky greens where blues and yellows stand out. Browns, oranges, shades of red and green are easily confused. Both types will confuse some blues with some purples and both types will struggle to identify pale shades of most colours.

However, there are some specific differences between the 2 red/green deficiencies.

Protanopia

Protanopes are more likely to confuse:-
1. Black with many shades of red
2. Dark brown with dark green, dark orange and dark red
2. Some blues with some reds, purples and dark pinks
3. Mid-greens with some oranges

Deuteranopes

Deuteranopes are more likely to confuse:-
1. Mid-reds with mid-greens
2. Blue-greens with grey and mid-pinks
3. Bright greens with yellows
4. Pale pinks with light grey
5. Mid-reds with mid-brown
6. Light blues with lilac

Tritanopes

The most common colour confusions for tritanopes are light blues with greys, dark purples with black, mid-greens with blues and oranges with reds.

The images show how the beautiful colours of the pigments are lost to people suffering with each type of dichromatic vision.

Monochromacy (achromatopsia)

Normal Vision

Monochromacy

People with monochromatic vision can see no colour at all and their world consists of different shades of grey ranging from black to white, rather like only seeing the world on an old black and white television set. Achromatopsia is extremely rare, occuring only in approximately 1 person in 33,000 and its symptoms can make life very difficult. Usually someone with achromatopsia will need to wear dark glasses inside in normal light conditions.

We have had several very concerned people contact us via this website because they or their children have been diagnosed by their optician with ‘total colour blindness’. Although we are unable to advise on the diagnosis of specific cases we have undertaken further research to try and understand why so many people are being told they are totally colour blind when in reality they are much more likely to have a severe form of red-green colour blindness. Our research has revealed that in many cases opticians have only received basic training on colour vision deficiency and some may therefore be incorrectly interpreting the results of the Ishihara tests.

If you have been diagnosed as ‘totally’ colour blind please follow the links to these two specialist websites for further information. If you think you do have the symptoms of achromatopsia ask your optician to refer you to a specialist who can confirm your condition.

www.achromat.org
www.achromatopsia.org

Statistics

There is general agreement that worldwide 8% of men and 0.5% of women have a colour vision deficiency. These figures rise in areas where there is a greater number of white (Caucasian) people per head of population, so in Scandanavia the figures increase to approximately 10-11% of men. By contrast in sub-Saharan Africa there are few colour blind people. Countries such as India and Brazil have a relatively high incidence of colour vision deficients because of the large numbers of people with mixed race genes in their genetic history.

The 8% of colour blind men can be divided approximately into 1% deuteranopes, 1% protanopes, 1% protanomalous and 5% deuteranomalous. Approximately half of colour blind people will have a mild anomalous deficiency, the other 50% have moderate or severe anomalous conditions.

Numbers of tritanopes/tritanomalous people and achromats is very small, perhaps 1 in 30-50,000 people.

Reliable statistics for people with an acquired form of colour vision deficiency are difficult to find but as many as 3% of the population could be affected because age-related deficiency is relatively common in the over 65s and therefore on the increase in the UK due to the rising numbers of elderly people per capita.

To put these statistics in context, an all-boys school in the Home Counties of England with 1000 pupils would have approximately 100 colour deficient students. 12-13 would be deuteranopes, 12-13 would be protanopes, 12-13 would have a form of protanomaly and 62 would have a form of deuteranomaly. About half of those with an anomalous condition would have a moderate to severe form of deficiency.

What Is Colorblindness and the Different Types?

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).

5% to 8% (depending on the study you quote) of the men and 0.5% of the women of the world are born colorblind. That's as high as one out of twelve men and one out of two hundred women. I am going to limit this discussion to protans (red weak) and deutans (green weak) because they make up 99% of this group.

Protanomaly (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 seen more weakly by the protanomalous viewer, 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.

Color normal        Color Deficient Dichromat

(source: critiquewall.com by Paul Martin)

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 (five out of 100 males):

The deuteranomalous person is considered "green weak". Similar to the protanomalous person, he is poor at discriminating small differences in hues in the red, orange, yellow, green region of the spectrum. He makes 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.

Dichromasy - can be divided into protanopia and deuteranopia (two out of 100 males):

These individuals normally know they have a color vision problem and it can effect their lives on a daily basis. They see no perceptible difference between red, orange, yellow, and green. All these colors that seem so different to the normal viewer appear to be the same color for this two percent of the population.

Protanopia (one out of 100 males):

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 (one out of 100 males):

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 him aside from being different names that every one else around him seems to be able to agree on.

In Conclusion:

It should be obvious there are several different kinds and degrees of color vision deficiencies. Protanomalous or deuteranomalous individuals can usually pass as a normal observer in everyday activities. They may make occasional errors in color names, or may encounter difficulties in discriminating small differences in colors, but usually they do not perform very differently from the normal except on color vision tests.

The protanope and deuteranope, on the other hand, can be severely color deficient. The real problem, as a protanope or deuteranope may see it, is there are far too many hue names (color names) used by most people without any obvious basis for using one instead of another. Why call something "orange" when it doesn't look different in any way from something else called green, tan, beige, or any of several other color names?

Click here for an excellent Powerpoint presentation by Dr. Rabin on colorblindness. The presentation is technical and mainly for the scientific community.

reference
--http://www.colourblindawareness.org
--http://colorvisiontesting.com/color2.htm