The Science of Color Vision: How We Perceive the World Around Us
In humans, color perception means the ability to distinguish different colors. The perception of colors is mediated by certain mechanisms in the retina and brain. But do you know that objects actually do not possess colors? It is the way they reflect light wavelengths that help us see colors.
The light spectrum ranges between ultraviolet light and red light, and within it is the visible spectrum. It is due to this spectrum that humans can distinguish more than 10 million colors.
How Do We Perceive Color In The World Around Us?
It is important to understand the psychological basis of color vision. Any abnormalities in color vision help us determine underlying health issues and their relevant treatments.
But first, we must be aware of how we perceive color in the world around us.
When light falls on an object, it absorbs some of that light. The rest is reflected. That reflected light enters the human eye and leads to color perception. For example, if light falls on an apple, the apple will absorb all of the light wavelengths except the wavelength we see as red. That red wavelength enters the human eye through the cornea, the outermost part.
The cornea will bend the light towards the pupil, and the pupil controls how much light hits the lens. The lens then focuses this light onto the retina, which has two types of nerve cells in the back of the eye.
These cells are rods and cones – collectively known as photoreceptors.
Rods are active when you are in dim or low light, and cones are activated in a bright environment. It is these cones that have the color-detecting molecules or photo pigments. There are three types of photopigments: red, green, and blue. Different types of cones are receptive to different wavelengths of light in the visible spectrum.
This was the science behind color perception.
So, when you see the apple’s reflected light in the daytime, it will activate the red cones. These cones will send a signal to the visual cortex of the brain via the optic nerve. The brain will process all the cones that were activated and their strength, and after processing the nerve impulses, you will see a color – red.
If the same apple is perceived in a darker environment, the light reflected off it will only stimulate the eye’s rods. When rods are activated, you only see shades of gray, and colors like red, green, yellow, orange, blue, purple, etc., are not distinguished.
Pathophysiology of Human Color Perception
Abnormal color vision is subdivided into congenital and acquired forms.
The color vision abnormalities caused by genetic disorders happen due to the genes encoding cones in your eyes. Such defects result in various outcomes featuring retinal degeneration, different progression rates, and loss of visual acuity. Similarly, rod dystrophies lead to late color vision abnormalities.
On the other hand, acquired color vision deficiencies occur due to disruptions to visual pathways or injuries.
The Most Common Types of Color Vision Deficiencies
Color vision deficiency is most commonly known as color blindness.
Color blindness means that a person cannot see colors in the traditional way because some nerve cells, or cones, in their eyes don’t work properly or are missing altogether. People with color blindness have trouble differentiating certain colors and shades. They also cannot perceive the blindness of colors. The most common cause of color blindness is an inherited genetic mutation.
So, before we discuss the types of color blindness, let’s understand the three types of cones that a person is normally born with;
Red Sensing Cones
Also known as L cones, these cones perceive long wavelengths around 560 nm.
Green Sensing Cones
Also known as M cones, these cones perceive middle wavelengths around 530 nm.
Blue Sensing Cones
Also known as S cones, these cones perceive short wavelengths around 420 nm.
In trichromacy, all three cone types are present and working. This is also known as full-color vision, in which a person can see all the colors on the visible light spectrum in a traditional way.
Most people in the world have all three types of cones. However, some of them have different categories of cone deficiencies, such as;
Anomalous Trichromacy
In anomalous trichromacy, a person has all three types of cones. However, one type isn’t sensitive to light in its normal wavelength. Due to this change, the person doesn’t see colors in a traditional way.
There are three further types of anomalous trichromacy;
● protanomaly (affecting red-sensing cones)
● deuteranomaly (affecting green-sensing cones)
● tritanomaly (affecting blue-sensing cones)
Dichromacy
In Dichromacy, one type of cone is missing. The person is left with two types of cones, usually S cones with L or M cones. Dichromacy results in color vision in which a person can only see wavelengths that the two cones can perceive. This is why it becomes difficult to differentiate fully saturated colors. The types of Dichromacy and their associated color blindness end in “anopia,” which means the absence of a specific color vision.
Monochromacy
Monochromacy is the condition in which a person has only one type of cone or no cone function at all. The result is very limited or no ability to see color. People with Monochromacy see the world in different shades of gray.
Owing to these categories of cone deficiencies, there are different types of color blindness, such as;
● Red-green color deficiency
● Blue-yellow color deficiency
● Blue cone monochromacy
● Rod monochromacy (achromatopsia).
Colors are an important part of our lives. They help us make memories, differentiate one thing from another, and live a normal and happy life. Understanding how humans perceive colors is very important to understanding any potential diseases or underlying disorders that can affect our vision throughout our lives. And if you ever want to know more about how your eyes work and perceive colors, visit the Healthy Vision Association for information-packed blogs and professional medical guidance.