The Best Test for Colour Blindness

Colour blindness (which experts call more accurately “Colour Vision Deficiency”) is the inability to see some colours or to tell some apart from others. The condition affects more than one in 20 males and a smaller but significant number of females.

What causes colour blindness?

We can see because of receptor cells at the back of the eye called rods and cones. Colour is seen via the cones, which distinguish red, green and blue. In some people, one kind of cone is not working, like a colour TV set on the blink.

The main cause is genetic – you get it from your parents or grandparents. But colour blindness can also result from disease and accidents. Some causes we know about include: an acquired brain injury; eye diseases such as macular degeneration, glaucoma and diabetic retinopathy; some drugs; and vitamin A deficiency.

Are there different forms?

The most common forms make it hard to pick out the red, yellow and green part of the spectrum and are popularly called Red-Green Colour Blindness. Rarer is the Blue-Yellow version. And there are some even rarer versions, including one where no colour can be seen – in fact there’s an island in the Pacific where 10% of the population can’t see colours at all.

Is it possible my child might have colour blindness?

It isn’t always easy to diagnose colour blindness in kids. Sometimes the effect is mild, and the child may not even know they aren’t seeing colours correctly. Often around the age of 4 a child might start having difficulty with naming colours or separating things by colour. If you are concerned, visit an optometrist, or ask your GP for a referral to an ophthalmologist.

Is the condition a problem – and can it be corrected?

Colour blindness is not a disease, it’s a condition. It cannot be cured. Discovering that you have colour blindness can make dealing with it in everyday life much more straightforward.

People use a range of strategies to make up for colour blindness. They might, for example, understand traffic lights by the position of the light if they can’t tell the colour. On a dark rainy night, that can be very hard! Generally it doesn’t prevent someone getting a standard driving licence, though not necessarily a commercial licence.

Colour blindness can make some occupations difficult or even illegal. Electricians, pilots, police, truck drivers, seamen and some jobs in the defence forces can be affected. Do you cut the red wire or the green one?

Of course it affects other professions in less dangerous ways, artists and craft workers, for example, though there’s no evidence it affects anyone’s ability to draw. Even simple daily activities like recognising ripe fruit can be tough.

There’s a growing number of apps that can help with everyday situations. Ophthalmologists do sometimes prescribe tinted lenses for some forms of the condition.

What’s the ideal test for colour blindness?

Developed 100 years ago, the Ishihara Test is still the best test to see if you have the condition. A more recent test, the 100-Hue Test or Colour Hue Test can provide more detailed information. There are online versions of both these tests, which of course you can try, but for a variety of reasons the online tests are not considered strong enough (computer colours vary, for example).

As there’s a great range in how colour blindness affects individuals, eye specialists now have a raft of further tests and equipment they can call on, including the RGB anomaloscope.

If you are concerned about colour blindness, you should see an ophthalmologist or optometrist. Some school health services also offer the test, or you can ask your optometrist next time you’re having your regular eye check-up.