What Causes Color Blindness?

Inherited (genetic) causes

Colour vision starts with three types of cone in the retina, sensitive to long (red), medium (green) and short (blue) wavelengths. Inherited colour blindness happens when the gene for one cone type is missing or altered, so that cone is absent or its sensitivity is shifted.

The genes for the red and green cones sit on the X chromosome, which is why red-green colour blindness is common and strongly favours men. The blue-cone gene is on a different chromosome, so blue-yellow deficiency doesn't show that male bias. Inherited colour blindness is stable: it doesn't get better or worse over time. Read more in the genetics of colour blindness.

Acquired causes

Colour vision can also change later in life. Because this kind of change can signal an underlying problem, a new or worsening colour difficulty is worth a professional eye exam. Common contributors include:

• Eye conditions: glaucoma, macular degeneration, cataracts and diabetic retinopathy can all affect colour perception.
• Systemic illness: diabetes and multiple sclerosis are among the conditions linked to acquired colour vision changes.
• Medications and chemicals: some drugs (for example certain heart and rheumatology medications) and industrial chemicals can alter colour vision.
• Ageing: the lens yellows gradually with age, which shifts how blues and yellows appear.
• Eye or brain injury: damage to the retina, optic nerve or visual areas of the brain.

Inherited vs acquired: how to tell

Inherited colour blindness is usually symmetric (both eyes the same), lifelong and red-green. Acquired colour vision problems can affect one eye more than the other, change over time, and often involve the blue-yellow axis. If your colour vision has changed noticeably, don't rely on an online screen, see an eye-care professional.

Curious where you stand? Take the free color blind test, then read about the types of colour blindness.