Color blindness is a genetic condition caused by a difference in how one or more of the light-sensitive cells found in the retina of the eye respond to certain colors. These cells, called cones, sense wavelengths of light, and enable the retina to distinguish between colors. This difference in sensitivity in one or more cones can make a person color blind.
Difference between vision of normal and color blindness
Color blindness is also called a color vision problem. A color vision problem can change your life. It may make it harder to learn and read, and you may not be able to have certain careers. But children and adults with color vision problems can learn to make up for their problems seeing color.
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 photo pigments found in cones. 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.
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.
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.
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.
Color perception in different types of color blindness
Blue-Yellow Color Blindness
Blue-yellow color blindness is rarer than red-green color blindness. Blue-cone (tritan) photo pigments 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 photo pigments 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.
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 photo pigments. 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.
History of color deficiency
The first scientific paper about color blindness was written by John Dalton in 1793 entitled “Extraordinary facts relating to the vision of colors“. Dalton himself was red green colorblind and as a scientist he took interest in this topic. He claimed that a colored liquid inside the eyeball is the source for a different color perception. This was proved wrong only after his death, when his eyes were examined and no such liquid was found.
After that Thomas Young and Hermann von Helmholtz were the first who described the trichromatic color vision. And once a theory for human color vision was ready, the basics of color vision deficiency weren’t far away.
Color Blindness by Nationality
One might expect the percentage of affected people to be relatively constant in all countries however this is far from the truth. In most Caucasian societies up to 1 in 10 men suffer, however only 1 in 100 Eskimos are color blind. There is no solid proof as to the cause of this however it is logical to assume that less of the ‘original Eskimos’ carried the defective gene, so the likelihood of it infecting the gene pool was quite a lot lower.
Causes and risk factors of Color Blindness
Color blindness occurs when light-sensitive cells in the retina fail to respond appropriately to variations in wavelengths of light that enable people to see an array of colors.
Inherited forms of color blindness often are related to deficiencies in certain types of cones or outright absence of these cones.
Besides differences in genetic makeup, other causes of color vision defects or loss include:
- Parkinson’s disease (PD). Because Parkinson’s disease is a neurological disorder, light-sensitive nerve cells in the retina where vision processing occurs may be damaged and cannot function properly.
- Clouding of the eye’s natural lens that occurs with cataracts can “wash out” color vision, making it much less bright. Fortunately, cataract surgery can restore bright color vision when the cloudy natural lens is removed and replaced with an artificial intraocular lens.
- Tiagabine for epilepsy. An antiepileptic drug known as tiagabine has been shown to reduce color vision in about 41 percent of those taking the drug, although effects do not appear to be permanent.
- Leber’s hereditary optic neuropathy (LHON). Particularly prevalent among males, this type of inherited optic neuropathy can affect even carriers who don’t have other symptoms but do have a degree of color blindness. Red-green color vision defects primarily are noted with this condition.
- Kallman’s syndrome. This inherited condition involves failure of the pituitary gland, which can lead to incomplete or unusual gender-related development such as of sexual organs. Color blindness can be one symptom of this condition.
Symptoms included in the Color blindness
Symptoms vary from person to person, but may include:
- Trouble seeing colors and the brightness of colors in the usual way
- Difficulty distinguishing between colors
- Inability to tell the difference between shades of the same or similar colors
- Often, the symptoms may be so mild that some people do not know they are color blind. A parent may notice signs of color blindness when a child is learning his or her colors.
- Rapid, side-to-side eye movements (nystagmus) and other symptoms may occur in severe cases.
- Double vision (diplopia)
- Achromatopsia – when an individual has a black, white, and gray vision only (an extremely rare condition)
- Eye pain
- Difficulty reading
- Drooping eyelid
- Constantly being corrected, when naming a color
What are the possible Complications of Color Blindness?
Complications linked to Color Blindness include:
- Career limitations
- Difficulty in performing certain regular/daily tasks
- Difficulty driving, especially distinguishing between traffic light colors
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.
The newer Cambridge Color Test uses a visual array similar to the Ishihara plates, except displayed on a computer monitor. The goal is to identify a C shape that is different in color from the background. The “C” is presented randomly in one of four orientations. When test-takers see the “C,” they are asked to press one of four keys that correspond to the orientation.
The anomaloscope uses a test in which two different light sources have to be matched in color. Looking through the eyepiece, the viewer sees a circle. The upper half is a yellow light that can be adjusted in brightness. The lower half is a combination of red and green lights that can be mixed in variable proportions. The viewer uses one knob to adjust the brightness of the top half, and another to adjust the color of the lower half. The goal is to make the upper and lower halves the same brightness and color.
The HRR Pseudoisochromatic Color Test is another red-green color blindness test that uses color plates to test for color blindness.
The Farnsworth-Munsell 100 Hue Test uses a set of blocks or pegs that are roughly the same color but in different hues (shades of the color). The goal is to arrange them in a line in order of hue. This test measures the ability to discriminate subtle color changes. It is used by industries that depend on the accurate color perception of its employees, such as graphic design, photography, and food quality inspection.
The Farnsworth Lantern Test is used by the U.S. military to determine the severity of color blindness. Those with mild forms pass the test and are allowed to serve in the armed forces.
Treatment of color blindness
There is currently no treatment for inherited color blindness. Color filters or contact lenses can be used in some situations to enhance the brightness between some colors and these are occasionally used in the workplace, but many color blind people find these actually confuse them further rather than help.
There is hope on the horizon for a ‘cure’ for inherited color vision deficiency using gene technology. A one-shot treatment for color blindness may begin human trials as soon as 2017, if current testing goes well. Jay Neitz, Ph.D. and Maureen Neitz, Ph.D., who are both professors of ophthalmology at the University of Washington, have already had success treating color blindness in monkeys using gene therapy. They have been studying color vision for much of their careers.
The new treatment that the Nietzes are testing uses an injection of an adeno-associated virus — a virus that doesn’t make humans sick — to get the genes into the cone cells of the retina.
For the current testing, an injection is made into the clear fluid in the center of the eye, and the virus finds the correct part of the retina to treat. If the treatment is found to work and approved for use, for some people color blindness could be reduced or cured with a single visit to the ophthalmologist.
Injections of other medications into the eye are already routine procedures in most ophthalmologists’ offices.
Some people use special lenses to enhance color perception, which are filters available in either contact lens or eyeglass lens form. These types of lenses are available from a limited number of eye care practitioners in the United States and other countries.
How can Color Blindness be prevented?
- Most cases of Color Blindness are inherited and hence, these may not be prevented
- However, early detection of the condition in children can help understand its nature and severity. This would allow the use of suitable measures to control any adverse effects and reduce learning difficulties later on
- Vision screening should be routinely performed, if taking certain medications are linked to vision deficiencies