Colour Blindness
In South Africa, colour blindness is a vision condition affecting the ability to distinguish certain colours, most commonly red and green.
It is not generally classified as a disability, and disclosure to employers or schools is only needed if it affects performance or requires accommodation.
Colour blindness (colour vision deficiency, or CVD) affects approximately 1 in 12 men (8%) and 1 in 200 women in the world.
Most colour blind people are able to see things as clearly as other people but they unable to fully ‘see’ red, green or blue light. There are different types of colour blindness and there are extremely rare cases where people are unable to see any colour at all. This is what you need to know.
What Are You Looking For?
1. Colour Blindness
i. Types of Colour Blindness
ii Degrees of Colour Blindness
iii. Diagnosis
iv. Causes of Colour Blindness
v. Treatment and Management
2. Other Visual Impairments
Colour blindness (colour vision deficiency, or CVD) affects approximately 1 in 12 men (8%) and 1 in 200 women in the world.
There are different causes of colour blindness. For the vast majority of people with deficient colour vision the condition is genetic and has been inherited from their mother, although some people become colour blind as a result of other diseases such as diabetes and multiple sclerosis or they acquire the condition over time due to the aging process, medication etc.
Most colour blind people are able to see things as clearly as other people but they unable to fully ‘see’ red, green or blue light. There are different types of colour blindness and there are extremely rare cases where people are unable to see any colour at all.
i. Types of Colour Blindness
The most common form of colour blindness is known as red/green colour blindness and most colour blind people suffer from this. Although known as red/green colour blindness this does not mean sufferers mix up red and green, it means they mix up all colours which have some red or green as part of the whole colour. For example, a red/green colour blind person will confuse a blue and a purple because they can’t ‘see’ the red element of the colour purple.
Similar problems can arise across the whole colour spectrum affecting all reds, greens, oranges, browns, purples, pinks and greys. Even black can be confused as dark green or dark blue. The main categories of colour blindness are:
1. Red–Green Colour Blindness (most common):
– Protanopia/Protanomaly > difficulty seeing red.
– Deuteranopia/Deuteranomaly
> difficulty seeing green.
2. Blue–Yellow Colour Blindness
– Tritanopia/Tritanomaly >
difficulty seeing blue or yellow.
3. Complete Colour Blindness (Monochromacy):
– Rod monochromacy > no colour, only shades of grey.
– Cone monochromacy > only one type of cone works,
very limited colour perception.
ii. Degrees of Colour Blindness
The effects of colour vision deficiency can be mild, moderate or severe so, for example, approximately 40% of colour blind pupils currently leaving secondary school are unaware that they are colour blind, whilst 60% of sufferers experience many problems in everyday life.
Statistically speaking most people with a moderate form of red/green colour blindness will only be able to identify accurately 5 or so coloured pencils from a standard box of 24 pencil crayons. Depending upon which type of the condition a colour blind person is suffering from they could see the set of pencil crayons similarly to the following images.
Achromatopsia is strictly defined as the inability to see color. Although the term may refer to acquired disorders such as cerebral achromatopsia also known as color agnosia, it typically refers to congenital color vision disorders (i.e. more frequently rod monochromacy and less frequently cone monochromacy).
In cerebral achromatopsia, a person cannot perceive colors even though the eyes are capable of distinguishing them. Some sources do not consider these to be true color blindness, because the failure is of perception, not of vision. They are forms of visual agnosia.
iii. Diagnosis
Colour blindness can be difficult to detect, particularly in children with inherited colour vision deficiency as they may be unaware that they have any problems with their colour vision. A child with a severe condition such as deuteranopia may seemingly be able to accurately identify colours which they can’t see (e.g. red) because they have been taught the colour of objects from an early age and will know for example that grass is green and strawberries are red even if they have no concept of their true colours.
If you have any eye test with an optometrist (a registered health professional who examines eyes, tests sight and dispenses glasses and contact lenses) they should test your colour vision as a matter of routine, but not all chains of opticians test routinely and with some you may have to request a colour vision test specifically and sometimes even pay for it as an extra.
iv. Causes of Colour Blindness
Colour blindness is a usually a genetic (hereditary) condition – you are born with it. Red/green and blue colour blindness is usually passed down from your parents. The gene which is responsible for the condition is carried on the X chromosome and this is the reason why many more men are affected than women.
There are estimated to be over 250 million colour blind people worldwide. The vast majority of people with a colour vision deficiency have inherited their condition from their mother, who is normally a ‘carrier’ but not colour blind herself.
Some people also acquire the condition as a result of long-standing diseases such as: Diabetes; Multiple sclerosis; Some liver diseases; and almost all eye diseases
The effects of colour vision deficiency can be mild, moderate or severe depending upon the defect. If you have inherited colour blindness your condition will stay the same throughout your life – it won’t get any better or worse.
Genetics
Color blindness is most commonly inherited from mutations on the X chromosome but the mapping of the human genome has shown there are many causative mutations—mutations capable of causing color blindness originate from at least 19 different chromosomes and 56 different genes (as shown online at the Online Mendelian Inheritance in Man (OMIM).
Two of the most common inherited forms of color blindness are protanopia and deuteranopia.
One of the common color vision defects is red-green deficiency which is present in about 8 percent of males and 0.5 percent of females of Northern European ancestry.
Some of the inherited diseases known to cause color blindness are:
Color blindness always pertains to the cone photoreceptors in retinas, as the cones are capable of detecting the color frequencies of light.
About 8 percent of males, but only 0.5 percent of females, are color blind in some way or another, whether it is one color, a color combination, or another mutation.
The reason males are at a greater risk of inheriting an X linked mutation is that males only have one X chromosome (XY, with the Y chromosome carrying altogether different genes than the X chromosome), and females have two (XX); if a woman inherits a normal X chromosome in addition to the one that carries the mutation, she will not display the mutation.
Men do not have a second X chromosome to override the chromosome that carries the mutation. If 5% of variants of a given gene are defective, the probability of a single copy being defective is 5%, but the probability that two copies are both defective is 0.05 × 0.05 = 0.0025, or just 0.25%.
v. Treatment and Mangement
There is currently no treatment for colour blindness.
Colour filters or contact lenses can be used in some situations to enhance the brightness between some colours and these are occasionally used in the workplace, but many colour blind people find these actually confuse them further rather than help.
″The American Optometric Association reports a contact lens on one eye can increase the ability to differentiate between colors, though nothing can make you truly see the deficient color.″ Optometrists can supply colored spectacle lenses or a single red-tint contact lens to wear on the non-dominant eye, but although this may improve discrimination of some colors, it can make other colors more difficult to distinguish.
A 1981 review of various studies to evaluate the effect of the X-chrom contact lens concluded that, while the lens may allow the wearer to achieve a better score on certain color vision tests, it did not correct color vision in the natural environment.
The GNOME desktop environment provides colorblind accessibility using the gnome-mag and the libcolorblind software. Using a gnome applet, the user may switch a color filter on and off, choosing from a set of possible color transformations that will displace the colors in order to disambiguate them. The software enables, for instance, a colorblind person to see the numbers in the Ishihara test.
Many applications for iPhone and iPad have been developed to help colorblind people to view the colors in a better way. Many applications launch a sort of simulation of colorblind vision to make normal-view people understand how the color-blinds see the world. Others allow a correction of the image grabbed from the camera with a special “daltonizer” algorithm.
Lenses that filter certain wavelengths of light can allow people suffering from a cone anomaly, but not dichromacy, to see a better spectrum of colors, especially those with classic “red/green” color blindness. They work by notching out wavelengths that strongly stimulate both red and green cones in a deuter- or protanomalous person, improving the distinction between the two cones’ signals. As of 2013, sunglasses that enhance colors for many colorblind people are available commercially.
There is hope on the horizon for a ‘cure’ for inherited colour vision deficiency using gene technology – for more information visit www.genevolve.com. This will involve injecting genetic material into the eye so is not for the faint-hearted! At the moment there have been no trials on humans but the process has been proved to work in monkeys.
For acquired colour vision deficiency, once the cause has been established and treated, your vision may return to normal.