#97 Colour Blindness (English)

Colour blindness is a colour vision deficiency. People with this condition perceive colours different from what most of us see.

What colour is a raspberry? Most of us would say red, but do we all see the same red? Colour vision depends on our eyes and brain working together to perceive different properties of light.The colour of light is determined by its wavelength. Longer wavelength corresponds to red light and shorter wavelength corresponds to blue light. Raspberries and other objects reflect some wavelengths of light and absorb others. The reflected light we perceive as colour. 

Rods and cones in the retina both contain photopigment molecules that undergo a chemical change when they absorb light. Rods contain only one photopigment, while cones contain one of three different photopigments. This makes cones sensitive to long (red), medium (green), or short (blue) wavelengths of light. The presence of three types of photopigments, each sensitive to a different part of the visual spectrum, is what gives us our rich colour vision.

Most of us have a full set of the three different cone photopigments and so we share a very similar colour vision experience, but others may be missing or have a defect on one of the photopigments, leading to colour blindness.

Forms of colour blindness

    •       Monochromatism: Either no cones available or just one type of them.

    •       Dichromatism: Only two different cone types, the third one is missing completely.

    •       Anomalous trichromatism: All three types but with shifted peaks of sensitivity for one of them. This results in a smaller colour spectrum.

Dichromats and anomalous trichromats exist in three different types according to the missing cone or in the latter case of its malfunctioning.

    •       Tritanopia/Tritanomaly: Reduced sensitivity to blue light (very rare).

    •       Deuteranopia/Deuteranomaly: Reduced sensitivity to green light (most common).

    •       Protanopia/Protanomaly: Reduced sensitivity to red light.

Causes of colour blindness

•       Inherited colour blindness (most common)

•       Physical or chemical damage to the eye, the optic nerve, or parts of the brain that process colour information.

•       Colour vision can also decline with age, most often because of cataract - a clouding and yellowing of the eye’s lens.

•       Side-effects from medication or other diseases such as diabetes.

Who is more likely to get colour blindness?

As many as 8 percent of men suffer from this condition while only 0.5 percent of women do. This is because the genes responsible for the most common, inherited colour blindness are on the X chromosome. Males only have one X chromosome, while females have two X chromosomes. In females, a functional gene on only one of the X chromosomes is enough to compensate for the loss on the other.

How do you know if you are colour blind?

The numbers are 12, 2, 42, 74, 6 (clockwise)

= colour vision tests!!

Eye care professionals use a variety of tests to diagnose colour blindness.

•       The Ishihara Colour Test is the most common test for red-green colour blindness.

•       The Cambridge Colour Test

•       The anomaloscope uses a test in which two different light sources have to be matched in colour.

•       The HRR Pseudoisochromatic Colour Test

•       The Farnsworth-Munsell 100 Hue Test

•       The Farnsworth Lantern Test is used by the U.S. military to determine the severity of colour blindness.

Can this condition by cured?

Nope, sorry :(

TWO IMPORTANT, FUN FACTS:

•        Dogs are not colorblind.

•        “What colour is this?” is the most annoying question you can ask your colourblind friend

PSB