Types of Color Blindness

Red-green colour blindness

This is by far the most common group. It comes from the long-wavelength (L, red) or medium-wavelength (M, green) cones. Reds, greens, browns and oranges can look similar, and some shades of purple and blue are hard to separate.

Deuteranomaly and deuteranopia

In deuteranomaly the green cone is present but its sensitivity is shifted towards red. It is the most common colour vision deficiency, affecting around 5% of men. In deuteranopia the green cone is missing altogether.

Protanomaly and protanopia

In protanomaly the red cone is shifted towards green; in protanopia it is missing. Besides confusing red with green, people with protan vision see reds as darker, which can matter for traffic and warning lights.

Blue-yellow colour blindness

Tritanomaly and tritanopia involve the short-wavelength (S, blue) cone. Blue and green, and yellow and pink, can be confused. Inherited forms are rare and affect men and women equally. Blue-yellow loss acquired later in life is more common and can be a sign of eye disease.

Complete colour blindness

Achromatopsia (rod monochromacy) means no working cones. People see in shades of grey, are very sensitive to bright light and usually have reduced sharpness of vision. Blue cone monochromacy is a related, even rarer condition.

What causes colour blindness

• Inherited: red-green deficiencies are passed on through the X chromosome, which is why they are far more common in men.
• Eye and brain conditions: glaucoma, diabetic eye disease, macular degeneration, cataract and optic nerve damage can change colour vision.
• Medicines and chemicals: some drugs, such as hydroxychloroquine and ethambutol, and some solvents can affect colour vision.
• Ageing: the lens yellows with age, which makes blues and purples harder to tell apart.

Living with a colour vision deficiency

Most people adapt well. Phone and computer settings offer colour filters, apps can name colours through the camera, and labelling clothes or cables helps. Some careers, such as pilot, electrician, train driver or police officer, require a colour vision standard, so it is worth knowing your type early.