Color blindness—officially called color vision deficiency (CVD)—is a common eye condition that changes how people perceive colors. For some, it means mixing up red and green; for others, it means seeing the world in shades of gray. Whether you’re learning about your own vision, supporting someone with CVD, or just curious, this guide covers everything you need to know about CVD: from its types to how it affects daily life.
CVD stems from issues with cone cells—the eye’s color-detecting cells (we have three types, for red, green, and blue light). When cones are missing or faulty, colors become hard to distinguish. Here are the most common types:
The rarest and most severe form of CVD, achromatopsia means no cone cells work properly. People with this condition:
- See the world only in shades of gray (red looks dark, blue looks bright).
- Struggle with bright light (many wear dark sunglasses indoors to cope).
- Often have other symptoms like poor vision, lazy eye (amblyopia), or involuntary eye twitching (nystagmus).
Only 1 in 30,000 people have achromatopsia—most inherit it from both parents.
The most common type of CVD (affecting ~1 in 12 men and 1 in 200 women), red-green CVD breaks down into two subtypes:
- Protanopia (Red Blindness): Missing red-detecting cones. People mix red with dark green (e.g., a stop sign might look dark green) and see purple as blue.
- Deuteranopia (Green Blindness): Missing green-detecting cones. Green looks gray or black, and light green blends with dark red (e.g., a green leaf might appear gray).
Doctors group these together because both make it hard to tell red and green apart—the “color blindness” most people refer to.
Rare (affecting ~1 in 10,000 people), tritanopia affects blue- and yellow-detecting cones. People with this:
- Mix up blue and yellow (e.g., a yellow banana might look blue).
- Can still see red and green clearly.
Unlike red-green CVD, tritanopia is often acquired (from eye damage) rather than inherited.
The mildest form of CVD, color weakness means cone cells work partially—not fully. People can distinguish bright, dark colors but struggle with light or washed-out shades. The three subtypes:
- Protanomaly (Red Weakness): Hard to tell red from green in dim light.
- Deuteranomaly (Green Weakness): The most common color weakness—mixes green and red in poor lighting.
- Tritanomaly (Blue-Yellow Weakness): Rare; struggles with light blue and yellow.
Most CVD tests are quick, non-invasive, and done in bright natural light. Here are the three most common methods:
The gold standard for screening—used by schools, doctors, and workplaces. It uses dots of similar shades but different colors to form numbers or shapes. People with CVD either can’t read the shape or see a different number (e.g., someone with red-green CVD might miss a “5” hidden in red dots).
The most accurate test for red-green CVD. It measures how much red or green light you need to match a yellow light—telling doctors both the type and severity of your CVD. It’s often used for job requirements (e.g., pilot screenings) where precise results matter.
A hands-on test where you match colored threads to a “standard” color. It’s slower than the Ishihara test and only tells you the type of CVD (not severity)—so it’s less common for large groups.
Most CVD is hereditary—passed down through the X chromosome (since men have one X chromosome, they’re far more likely to inherit it). Rarely, CVD is acquired from:
- Eye diseases (cataracts, glaucoma, or retinal damage).
- Medications (e.g., some antibiotics or heart drugs).
- Aging (cone cells weaken over time).
Hereditary CVD can’t be cured—but there are ways to make daily life easier:
- Color-tinted glasses/lenses: Brands like EnChroma filter light to enhance color contrast, helping people with red-green CVD tell colors apart.
- Digital tools: Apps like ColorBlind Pal let you take photos and adjust colors for better visibility.
For acquired CVD (e.g., from cataracts), treating the underlying cause (like cataract surgery) may improve color vision.
CVD doesn’t just change how you see colors—it can impact:
- Jobs: Some careers require normal color vision (pilots, electricians, graphic designers, doctors) because mistakes could cause accidents or errors.
- Everyday tasks: Choosing clothes (e.g., matching socks), cooking (telling if meat is done), or reading traffic lights might take extra effort.
- Social moments: Missing color-coded cues (e.g., a friend’s “red” shirt looks brown) can lead to confusion or embarrassment.
But with awareness and tools, many people with CVD live full, independent lives—especially when others understand their needs.
Color vision deficiency is more common than you think—and it’s nothing to feel ashamed of. By learning about CVD, you can support yourself or others and make the world a more inclusive place for everyone who sees color differently.
