Colour Blindness

 

This week my eye post is about colour blindness, my maternal grandfather was colour blind. This is a condition that affects around 8% of men and only 0.5% of women. It is estimated that 300 million people are colour blind.

The huge gender difference exists because the most common type is linked to the X chromosome.

Colour blindness is a colour vision deficiency, not a total inability to see colour. In fact, 99% of people with “colour blindness” still see colours, just with reduced discrimination between certain hues.

There are different types of colour blindness with most cases fall into three major categories:

Protan defects – reduced sensitivity to red light

Deutan defects – reduced sensitivity to green light

Tritan defects – reduced sensitivity to blue light
These correspond to the three cone types in the eye.

Red–green colour blindness is by far the most common, affecting 95–98% of people with colour vision deficiency. This is sex linked and recessive, passed through the mother. A father cannot pass red–green colour blindness to his sons. If a woman is red–green colour blind, all her sons will inherit it.

Colour blindness ranges from mild to absolute although it is rare for someone to have absolute which means they see everything in greyscale

People with strong colour blindness may distinguish only 20 hues, compared to over 100 for those with typical colour vision.

This condition may cause some to feel overlooked or misunderstood, as others often don’t realise how much it affects daily tasks.

Being asked “What colour is this?” is widely considered the most annoying question to colour‑blind people.

Colour blindness is detected through colour vision tests that check how well someone can distinguish between different colours. These tests are simple, non‑invasive, and usually take only a few minutes.

The most common test is the Ishihara Colour Plates

The test shows a series of circles filled with coloured dots. Inside each circle is a number or pattern made of dots in a different colour. People with red–green colour blindness often cannot see the number, or they see a different number.

There are other tests such as the Farnsworth D-15 test, Anomaloscope, HRR (Hardy–Rand–Rittler) Test. Online screening tests, however, these can give an indication but are not fully reliable because screen brightness and colour calibration vary.

Babies are born colour blind; full colour vision develops by about 6 months.

It’s possible—though rare—to be colour blind in one eye only (unilateral dichromacy).

The first scientific paper on colour blindness was written by John Dalton in 1794.