Colour blindness (or colour vision deficiency) is the name given to the condition where people find it difficult to identify or distinguish different colours. There are colour blind tests that you can take online to detect the presence and type of colour blindness. The Ishihara test is one of the most common, and here we’ll show you how this simple test works.

What is colour blindness?

How do you test for colour blindness?

There are many colour blind tests that detect the presence and type of colour blindness. The Ishihara test is a common one that was developed in 1917 by Japanese ophthalmologist, Shinobu Ishihara. It’s become one of the most common ways to test for red and green colour deficiencies, particularly in children. The test involves identifying the number or shape contained within a series of different coloured dots, also known as Ishihara plates.

Other common colour vision tests involve colour arrangement in which you’re asked to arrange colours in order of their shade or to identify matching colours.

Some of these colour blind tests are available online such as the City University Test (developed by City University London) and the Farnsworth D-15 test. These can be more useful in detecting blue light deficiencies, which the Ishihara test doesn’t cover.

While online colour blind tests are a useful indication of a colour vision deficiency, for a proper diagnosis book an eye test and ask your optician to add one to your visit.

Book an eye test

How does the Ishihara colour blind test work?

You’ll easily recognise an Ishihara test — it’s largely used on children to identify types of colour deficiencies — and is sometimes available online.

Your optician will have a book made up of 38 different plates, known as pseudoisochromatic plates. Each plate is printed with different coloured dots of differing brightness, density and size. The dots are arranged so that those of a similar colour form a number or shape among a background of dots in a different colour.

They will show you a range of these plates and ask you to identify the hidden shape or number. Colours that may at first seem equal (or ‘iso) to your brain, are shown to you together and it’s up to your brain and eyes to detect the difference in order to see the hidden shape or number. People with normal colour vision are able to work out the false (or ‘pseudo’) similarity between the two colours and see the hidden shape or number with no problem.

If you are unable to identify some or all of the hidden figures it will indicate a colour vision deficiency and your optician will be able to make a diagnosis of colour blindness.

Check your vision with our colour blind test below

Click here to download or print the Ishihara colour blind test.

Download PDF

There are many other types of eye tests that your optician might perform during an eye examination, find out more by visiting our Snellen test, Eye dilation exam, and automation refraction test pages.

The Ishihara test is used to detect the most common types of colour blindness, which are categorised as red-green colour deficiencies (known as protanomaly and deuteranomaly).

These are general terms that cover a range of types and severities, but broadly mean that people are unable to see or differentiate colours that have red or green as part of the whole colour. So for example, people with a red deficiency will find it difficult to see the difference between blue and purple because they are unable to detect the red properties of purple. To find more information, visit our colour blindness page.

Your optician might carry out a colour arrangement test too, to confirm the results from the Ishihara test, as well as testing for the blue-light deficiency (tritanomaly), which an Ishihara test doesn’t test for.

It’s likely that red-green colour deficiency would be picked up during childhood, and opticians may include an Ishihara test during a children’s eye test to spot this early. But colour blindness can happen at any age and can often develop as a result of certain health conditions, like diabetes and multiple sclerosis, or as a consequence of the eye disease glaucoma. Medications or exposure to certain chemicals can also cause colour deficiencies.

So if you notice any changes in your colour vision, you should see your optician who can check this for you. Colour vision tests aren’t part of our usual eye tests, so just let us know if you’d like one.

Unfortunately, there is currently no known cure or treatment for inherited colour blindness. Those with the condition will find that they can adapt to it to some extent but may not be able to pursue professions where accurate colour vision is required. If a colour vision deficiency is developed as a result of illness, injury or medication, addressing the underlying condition may help.

Some colour blind tests online can give an indication of a possible problem with your colour vision, but they’re not always very reliable and can ultimately never provide an official diagnosis. For this reason, online vision tests should never replace a visit to your optician.

If you’d like a colour deficiency test for you or your child, book an eye test and ask your optician to add one to your visit. To find out more information, visit our eye tests hub.