Color blindness is a condition often misunderstood as a condition in which an individual is unable to see any colors—as if the world consists of only shades of black and white.
On the contrary, color blindness is a very complex condition entailing a variety of color discrimination deficiencies, rather than complete lack of color.
How Color Blindness is Determined
There are several different types of color blindness, which can vary from confusion of two color families to complete lack of color distinguishability, although the later is quite rare.
To best understand the various types of color blindness, it is helpful to have a basic understanding of what color is and how the eyes and brain distinguish one color from another.
Vision is created via stimulation of specialized cells called photoreceptors. Photoreceptors are located within the thin, back-most structure of the eye, the retina.
Photoreceptors are stimulated when a light wave within its sensitivity range reaches the retina. You can think about this almost like a “color sensor”—once the photoreceptor (sensor) detects a given wavelength, it sends a neurochemical signal to the brain via the optic nerve for image processing.
There are two main categories of photoreceptors in the eyes—rods and cones.
Rods are located more peripherally, and are responsible for detecting motion and helping with sight in dim lighting conditions.
Cones are located throughout the retina, but are more condensed centrally to make up the macula of the retina.
The macula is the area of the eye containing the most photoreceptors per unit of space, meaning it is responsible for detecting fine detail, color, and is responsible for our sharpest vision.
To further breakdown understanding photoreceptors, cones can be sub-categorized into three types—S-cones, M-cones, and L-cones.
The name of the cone corresponds to the wavelength of light the cone is stimulated by—short (blues), medium (greens), or long (reds).
Individuals with normal color vision are thus referred to as trichromats, “trichrome” meaning they have all 3 types of cones.
The color we perceive via vision is created by the wavelength of light an object gives off.
This is a very complex process, so we’ll explain it the best we can here without getting into too many of the fine details.
Light itself is energy in its purest form, it makes up the electromagnetic spectrum ranging from wavelengths we cannot see (gamma-rays, X-rays, etc.) to visible light. back to wavelengths too fine for us to see (infrared light, radio waves, etc.).
Light, therefore, encompasses all colors. It is easiest to think of light being the color white—composed of all wavelengths in an equal amount.
An object, such as a green ball, appears to us as being the color green based upon the material of the ball and the coating applied to the ball to make it green.
The coating and material absorb all wavelengths of light except for the green wavelength. Instead of absorbing the green wavelength, it reflects the green wavelength.
The now isolated green wavelength of light then enters our eyes and is detected by the M-cones, which send a signal to the brain to tell us the ball is green.
Thus, color—as we see it—depends on the wavelength of light reflected off of a given object.
Different hues of colors, for example hot pink from pale pink, are created depending on the coating of an object and what light is absorbed/reflected. Hot pink absorbs slightly different wavelengths than pale pink. The same goes for aqua blue vs royal blue.
Mixtures of colors, for example blue + red = purple, are created by the accumulation of the various stimuli received from photoreceptors by the brain. Thus, we can see a painting with thousands of different colors and hues because the brain summates all of the different colors during image processing.
Ultimately, the color possibilities are endless!
Now that we have an understanding of what color is, we can discuss what happens when someone is colorblind.
What is Color Blindness?
Like light, color blindness is also on a spectrum ranging from the inability to distinguish any color on the visible spectrum to color confusion.
Monochromacy is the condition in which an individual has only one type of photoreceptor. For example, if a person had only rods, he/she would not be able to detect varying wavelengths of color and would see the world in only black and white.
Similarly, this would occur if an individual only had 1 type of cone, as all wavelengths of light would be perceived as the same color red, for example. This individual would theoretically only be able to see in shades of red, which is actually perceived as just in black and white.
Monochromacy, also referred to as achromatopsia, is a very rare condition. In fact, it is estimated to only affect every 1 in 33,000 individuals.
A different type of color blindness occurs when an individual is missing one type of cone. These individuals are referred to as dichromats.
These individuals are still able to see some color, but their perception of color is skewed due to the fact that there are only two types of cones rather than the normal three types.
Individuals who are missing L-cones are called protanopes, meaning they do not have cones that absorb longer wavelengths of color like reds.
These individuals often mix up dark shades of colors such as red and black, dark orange and dark red, purples and dark pinks, as well as middle-spectrum wavelengths like green and orange.
Individuals who are missing M-cones are called deuteranopes, meaning they do not have cones that absorb middle-wavelength colors like green.
These individuals often mix up brighter colors like red and green, green and yellow, and pinks and grey.
Individuals who are missing S-cones are called tritanopes, meaning they do not have cones that absorb short-wavelengths of light like blue.
These individuals often mix up colors like green and blue, red and orange, and purple and black.
A person does not need to completely lack a type of cone to be color deficient, however. An individual can also be color weak, or an “anomalous trichromat”.
These individuals have all three types of cones, but the ratio of the amount of each type of cone is skewed, making one type of cone lower in number, or color weak.
Color for these individuals can range from almost normal, to almost dichromatic.
L-cone weak, or red-weak, color deficiency is referred to as protanomaly. These individuals have difficultly differentiating different shades of red and green.
M-cone weak, or green weak, color deficiency is referred to as deuteranomaly. This is the most common type of color deficiency, resulting in difficult differentiating differences in shades red and green.
S-cone weak, or blue weak, color deficiency is referred to as tritanomaly. These individuals may struggle to differentiate between blues and yellows.
What Causes Someone to Be Color Blind?
Most cases of color blindness are a result of genetics and are passed down from generation to generation—although just because a parent is color blind does not necessarily mean his/her child will be.
Color blindness is more common in men than women, affecting close to 8% of men and 0.5% of women globally.
Color blindness can be acquired over time, however, and has been seen in individuals with advanced glaucoma, macular degeneration, multiple sclerosis, and with prolonged use of some medications.
If you, or someone you know, thinks they may have a color deficiency, be sure to make an appointment to talk with your eye doctor today.
There are various types of tests that can help detect and determine what type of color deficiency an individual has, and suggest appropriate treatments or vision rehabilitation tools to make the most out of life with color blindness.