Color blindness, also known as color vision deficiency, is the decreased ability to see color or differences between colors. It affects around 1 in 12 men and 1 in 200 women worldwide. The most common types of color blindness are red-green color blindness, where it’s hard to tell the difference between reds, greens, browns, and oranges, and blue-yellow color blindness, where it’s hard to tell the difference between blues and greens and yellows and pinks. In this article, we’ll take a closer look at red-green color blindness, which makes up 99% of all color blindness cases.
What is red-green color blindness?
Red-green color blindness is an inherited genetic disorder that affects how the photoreceptor cone cells in the retina respond to color. Trichromatic vision relies on three types of cone cells – those responsive to red, green, and blue light. In red-green color blindness, there is a defect in either the red cones or green cones, leading to trouble distinguishing between reds, greens, browns, and oranges.
There are two main types of red-green color blindness:
Protanopia (red deficiency)
This is caused by a defect in the red cones. People with protanopia are unable to detect any red light and may have trouble distinguishing between blues and purples as well.
Deuteranopia (green deficiency)
This is caused by a defect in the green cones. People with deuteranopia are unable to detect any green light and may also mix up blues and yellows.
What is the prevalence of red-green color blindness?
Red-green color blindness affects up to 8% of men and 0.5% of women worldwide. The gene responsible for red-green color blindness is passed on the X chromosome. Because men only have one X chromosome, a single copy of the defective gene is enough to cause color blindness. Women have two X chromosomes, so even if they inherit one defective gene, the second X chromosome will usually have the working gene to offset it.
Some key prevalence statistics:
- 1 in 12 men are color blind
- 1 in 200 women are color blind
- 99% of cases of color blindness are red-green
- 8% of men have red-green color blindness
- 0.5% of women have red-green color blindness
The rate of red-green color blindness varies around the world based on ethnicity. Here are the rates among populations in the United States:
|Prevalence in Males
As you can see, the rates are highest among Caucasian males and lowest among Hispanic males. But overall, red-green color blindness impacts 1 in 20 men across all ethnicities.
How do people with red-green color blindness see the world?
People with red-green color blindness do not see the world in black and white. But they do have trouble distinguishing between certain shades of red, green, brown, and orange.
So what does the world look like through the eyes of someone with red-green color blindness? Here are some examples:
- Ripe tomatoes may look nearly identical to the green leaves around them
- Purple flowers may look exactly the same as blue flowers
- Red apples mixed in a bowl with green pears are indistinguishable
- Orange traffic lights are very difficult to tell apart from yellow or white lights
- Red and brown clothing items appear similar
- Pink looks very pale, almost white
- Maps with red and green markings are useless
In general, any situation where red needs to be distinguished from green or brown is challenging for someone with red-green color blindness. Primary colors may appear washed out or indistinct from each other. It takes more concentration and attention to detail to work around the inability to detect those colors.
Diagnosing red-green color blindness
Red-green color blindness is most commonly diagnosed using tests where the patient has to identify numbers or symbols hidden within colored dot patterns. Some examples include:
Ishihara Color Test
This test displays circles of many colored dots. Within each circle of dots is a number or shape that is only visible for people with normal color vision. People with red-green color blindness will not be able to see the shape.
Farnsworth D-15 Test
This test has small movable color samples. The patient needs to arrange them in order from one hue to another. People with red-green color blindness will have difficulty ordering and distinguishing between the red, green, and brown samples.
Lanthony Desaturated 15 Hue Test
This test has panels with fifteen shades of desaturated color ranging from purple to red. The patient arranges the caps in order based on hue. Mistakes in ordering indicate color blindness.
This instrument mixes red and green light beams. The patient looks through the anomaloscope and adjusts the levels of each beam until they appear identical. People with normal vision will see the blended color as yellow. People with red-green color blindness will see something else.
Early diagnosis is recommended to allow for adaptive strategies in school and in choosing a career. Workplaces may test for color blindness if normal color perception is required for safety reasons.
Coping with red-green color blindness
While there is currently no cure for red-green color blindness, there are ways to manage it:
- Use color identifiers like labels or markings if color coding is used
- Rely more on texture and pattern rather than color
- Use tools like color identifier apps on smartphones that detect and name colors
- Learn to take cues from context – grapes next to apples in the cafeteria are likely green and red respectively
- Ask others to identify and confirm colors if needed for a task
- Avoid careers that require normal color vision for safety reasons
- Sit closer to the front in classrooms if colorchalkboards are used
- Use lighting adjustments and tinted glasses or contact lenses to make some colors easier to distinguish
With some adaptive strategies, people with red-green color blindness can work around their condition in daily life. New assistive technologies are also constantly emerging, like augmented reality glasses that could one day superimpose the names of colors in real time for the wearer.
How is red-green color blindness different from green-red color blindness?
While they may sound alike, red-green and green-red color blindness are two distinct conditions:
Red-green color blindness
- Inability to distinguish reds, greens, browns, and oranges
- Most common type of color blindness
- Sex-linked genetic disorder on the X chromosome
- Affects up to 8% of men and 0.5% of women
- Caused by defect in red or green retinal cone cells
Green-red color blindness
- Extremely rare
- Not an inherited trait
- Acquired from damage to the eye or brain
- Main symptom is confusing greens for reds, and vice versa
- Can result from stroke, tumor, medication side effects, etc.
The key difference is that green-red color blindness is not a genetic condition but rather an acquired form of color confusion. It may result from physical trauma, a neurological disorder, or toxicity. Since it doesn’t involve missing or defective cones, it is very rare compared to hereditary red-green color blindness. Both conditions make it hard to tell greens and reds apart, but green-red color blindness isn’t present from birth and has many more possible causes.
In summary, red-green color blindness is a common hereditary disorder that makes it hard to distinguish between reds, greens, browns, and oranges. It is a sex-linked trait affecting up to 8% of men but only 0.5% of women. Green-red color blindness is extremely rare and refers to acquired confusion between red and green, not an inborn defect. Both conditions may make it hard to tell red and green apart, but only red-green colorblindness is a genetic form of color vision deficiency. With adaptive strategies and emerging assistive technologies, people with red-green color blindness can manage their condition and work around their limitations in perceiving color.