Is the Ishihara Test Accurate?
For red-green colour blindness, yes: the Ishihara test catches most moderate and strong cases. It does not test blue-yellow vision, can miss mild cases and doesn't measure severity.
What the Ishihara test does well
Studies over many decades have found it highly sensitive for inherited red-green deficiency, and it is quick, cheap and easy to give. That is why it is the first test in most clinics, schools and job medicals.
What the Ishihara test misses
- Blue-yellow (tritan) deficiency: there are no tritan plates.
- Severity: a pass or fail count doesn't show how strong a deficiency is.
- Some mild anomalous trichromats pass, and some people with normal vision make a few errors.
- Classification plates don't always separate protan from deutan.
What can change your result
- Light: the plates are designed for daylight; warm indoor light changes the colours.
- Plate condition: old, faded or dirty books become easier or harder to read.
- Screens and printers: online and printed copies of the plates don't reproduce the colours exactly.
- Time and fatigue: looking too long can make a faint number appear.
Ishihara test compared with other colour vision tests
| Test | What it does | Detects | Used for |
|---|---|---|---|
| Ishihara plates | Read numbers in dot plates | Red-green | Screening |
| HRR plates | Find shapes in dot plates | Red-green and blue-yellow, with severity | Screening and grading |
| Farnsworth D-15 | Arrange 15 coloured caps in order | Moderate to strong deficiency of any type | Jobs, grading severity |
| Farnsworth-Munsell 100 Hue | Arrange 85 caps in fine steps | Subtle and acquired defects | Detailed assessment |
| CAD test | Spot a moving coloured square on a screen | Type and severity | Aviation medicals |
| Lantern tests | Name coloured lights | Ability to read signal lights | Maritime, aviation, rail |
| Anomaloscope | Match a yellow light with red and green | Exact red-green type and severity | Diagnosis (reference test) |
Are online Ishihara tests accurate?
Copies of the printed plates on websites are not reliable: scanning and screen colours change them. A test designed for screens, with colours calculated for a standard display, works better as a screening. Ours detects moderate and strong deficiencies but, like any screen test, can miss mild ones.
Accuracy questions
Can the Ishihara test be wrong?
Yes, occasionally. People with mild deficiencies can pass, and people with normal vision can miss faint plates in poor light. A retest or a different test usually settles it.
What is the best alternative to the Ishihara test?
It depends on the question. The HRR adds blue-yellow plates and grading, the D-15 shows practical severity, and the anomaloscope gives an exact diagnosis of red-green type.
Does the Ishihara test detect tritanopia?
No. It only screens red-green deficiency. Blue-yellow deficiency needs tests such as the HRR, the CAD test or our blue-yellow plates.
Check both red-green and blue-yellow vision.
Take the colour blind test