Color blindness

Medical quality assurance by Dr. Albrecht Nonnenmacher, MD at June 25, 2016
StartDiseasesColor blindness

Color blindness refers to one's inability to properly see certain hues of color that the average person can distinguish. This can include red-green color deficiency, blue-yellow color deficiency, or complete color blindness, which is the rarest of the three distinct forms. Males are at a much higher risk of being born with the genetic condition that results in this condition because of the mechanism by which individuals inherit color blindness. 

Contents

Definition & Facts

Color blindness is a condition most commonly observed in males that results in partial or complete loss of color vision. This is due to an X-linked trait that causes an individual to be incapable of discerning certain shades of color. Surprisingly, approximately 8% of men worldwide exhibit some form of color blindness, making it a relatively common genetic condition. Conversely, only 0.5% of women are color blind.

Red-green color blindness is the most frequently observed form and is displayed by nearly 99% of color blind individuals. Blue-yellow color blindness is significantly less common, is not X-linked, and can be autosomal recessive (tritanopia) or autosomal dominant (tritanomaly). Males are not at a higher risk of exhibiting blue-yellow color blindness than females. Total color blindness is also known as achromatopsia, and this form of true color blindness is very rare, only occurring in about 1 out of every 33,000 Americans.

Though some color blind individuals feel handicapped, most people exhibiting color blindness find effective ways to cope with their condition and live a normal life. Color blindness is not recognized as a disability under U.S law. Contrary to popular belief, dogs are not completely color blind though do perceive a more limited spectrum of colors than humans.

Symptoms & Complaints

Red-green color blindness causes individuals to have the inability to distinguish hues of red and green. Blue-yellow color blindness results in an individual who has difficulty discriminating among hues of blue, green, yellow, and oftentimes even red.

Total color blindness causes an individual to be completely incapable of perceiving color. This is what people tend to imagine when they think of the vision of dogs (which, as stated earlier, is completely false). Furthermore, individuals with achromatopsia tend to experience sensitivity to light as well as reduced sharpness in their vision.

Causes

Red-green color blindness is passed down through X-linked recessive inheritance, which means that it corresponds to a genetic mutation located on the X chromosome in humans. Males have only one X chromosome, as well as a Y chromosome, while females have two X chromosomes. This explains why males are almost exclusively diagnosed with this form of color blindness. The genetic mutation involved with red-green color blindness negatively impacts the red and green retinal photoreceptor cells

If a female has red-green color blindness, then she will pass on an X chromosome to her offspring that contains that same genetic mutation that results in the condition. If her child is a boy, then that boy will definitely have red-green color blindness since the female passed on the X chromosome while the male partner passed on his Y chromosome. However, if she has a girl, then that girl will be a genetic carrier of red-green colorblindness (only have the mutation on one of her X chromosomes) but will not actually display symptoms of the condition.

Blue-yellow color blindness works by a slightly different mechanism. The genetic mutation that results in this condition is located on chromosome 7, which is an autosome. X and Y chromosomes, on the other hand, are sex chromosomes and function in a slightly different way. Therefore, males and females both have an equal chance of inheriting this recessive condition based upon the genetic fingerprint of their parents. However, this form of color blindness is not nearly as common as red-green colorblindness, which is why color blindness is most often associated with males.

Achromatopsia, or complete color blindness, is very rare and not nearly as well understood as the previous two conditions. The likelihood of a male inheriting the condition is equivalent to that of a female. There have been cases of total color blindness where the individuals do not have any of the genetic mutations discovered by scientists. There is still much to research and discover about this particular form of color blindness.

Diagnosis & Tests

The diagnosis of color blindness is fairly straightforward and often performed early on in a person's life. The primary screening test used for diagnosis is known as the Ishihara color plates and are basically images of patterns of color containing numbers on the inside. These are used to determine the severity and degree of color deficiency observed. A similar test that is often used on patients is known as the Hardy-Rand-Rittler (HRR) test, which works based upon a similar principle. 

Treatment & Therapy

Unfortunately, color blindness is a condition that, to this date, cannot be cured or properly treated. However, as with many conditions, individuals learn to cope with it in their own unique way. Many color blind patients develop recognition patterns that are used to effectively discern different colors. They utilize factors such as brightness, specific hue, location, and intensity to judge what they are observing. This is especially important for certain daily functions such as obeying traffic lights. 

Some advanced, innovative technologies have been introduced to help color blind individuals "normalize" their vision. These include specialized lenses or tinted glasses that are specific for people with color deficiencies. These are relatively new and will likely become more effective over time as they are being consistently improved to accommodate those with color deficiencies.

Furthermore, because a significant portion of people exhibit color blindness, many smartphone companies and app developers have adjusted their apps or even added new settings specific to color blind individuals to help them use and navigate the app with ease. 

Prevention & Prophylaxis

Inherited color blindness, which is virtually all forms of color blindness that are not caused by damage to the optic nerve or retina, is practically impossible to prevent. The only definite way to prevent color blindness is to receive genetic testing and if confirmed to be a carrier, abstain from having children.

Color blindness does not significantly diminish a person's quality of life, and one can live a normal, happy life while color blind. The vast majority of individuals who are color blind have no significant negative impacts on their life caused by the condition and can function perfectly fine in society.