Ishihara Test: How the Color Vision Test Works
Numbers made of colorful dots – almost everyone knows the Ishihara test from the eye doctor, a school screening or a job medical. Here is how the plates work and what they tell you.
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What is the Ishihara test?
The Ishihara test is a color vision test for detecting red-green color blindness. It was developed in 1917 by Japanese ophthalmologist Shinobu Ishihara, originally to examine military recruits. It is still the most widely used color vision test in the world.
How the Ishihara color plates work
Each plate is made of many circles of different sizes and brightness. Some of them form a number or a line, the rest form the background. Number and background differ only in hue, not brightness – chosen so that the colors lie on the "confusion lines" of people with red-green color blindness. People with normal color vision see the number; people with red-green color blindness don't see it, or see a different one.
Plate types
| Plate type | What happens |
|---|---|
| Demonstration plate | Read by everyone – shows the test was understood. |
| Transformation plate | Normal vision sees one number, red-green color blind people another. |
| Vanishing plate | Only people with normal color vision see the number. |
| Hidden digit | Only people with red-green color blindness see the number. |
| Classification plate | Helps tell protan from deutan. |
There are editions with 38, 24 and 14 plates. For children who cannot read numbers yet, there are plates with winding lines to trace.
How the test is done and scored
- Plates are shown in daylight at about 75 cm (30 inches).
- Each plate is viewed for only a few seconds.
- The number of correctly read plates is counted; above a certain number of errors, color vision is considered abnormal.
Take an Ishihara test online
Our free red-green color blind test works on the Ishihara principle: 22 plates, tap to answer, result with type and strength. Here is what a plate looks like – which number do you see?
Limits of the Ishihara test
- It detects only red-green deficiencies, not blue-yellow color blindness.
- It does not measure severity precisely – eye doctors use an anomaloscope for that.
- Online versions depend on your screen (brightness, color settings, night mode). An online test is a good first check, not a diagnosis.
For children, a playful start helps – see our color blind test for kids.
Frequently asked questions
Who invented the Ishihara test?
Japanese ophthalmologist Shinobu Ishihara, in 1917.
How many plates does the Ishihara test have?
The standard edition has 38 plates; there are shorter versions with 24 and 14. Our online test uses 22.
Is an online Ishihara test accurate?
It gives a good first indication. Because screens display colors differently, it does not replace an eye exam.