Published by ColorVision Editorial Team. This educational content is not individual medical advice. Read our editorial policy and test methodology.
Quick answer
Conventional Ishihara plates screen mainly for red-green colour-vision differences by asking someone to identify figures made from coloured dots. An online Ishihara-style activity can be educational, but display and lighting conditions mean it is not a clinical diagnosis.
When to seek care: Use a qualified eye-care professional for a formal assessment, especially for a new visual change or an occupational requirement.
The Ishihara Test Explained
The Ishihara test is the most widely used colour vision screening test in the world. Named after its creator, Dr. Shinobu Ishihara, it has been the standard tool for detecting red-green colour blindness since 1917. Despite being over a century old, it remains highly effective, inexpensive, and fast to administer.
History
Dr. Shinobu Ishihara (1879–1963) was a Japanese ophthalmologist who developed the test during his time at the Tokyo Army Medical School. The original purpose was to screen Japanese military recruits for colour vision deficiency. The test was first published in 1917 and has since been updated in several editions, with the modern version comprising 38 plates.
The test has seen remarkably little fundamental change since its creation — a testament to its effectiveness. It is now used globally in ophthalmology clinics, military screening, occupational health assessments, and school health checks.
How Does It Work?
The Ishihara test uses pseudo-isochromatic plates — a design principle based on the science of colour confusion in colour vision deficiency.
The Science Behind the Plates
Each plate consists of a large circle filled with hundreds of small dots varying in:
- Size — varied randomly to prevent edge detection as a cue
- Colour — from carefully chosen hue sets that exploit colour confusion
- Brightness (luminance) — carefully matched between figure and background
The dots form a pattern — typically a number or path — that is visible only when the viewer can distinguish the specific colours used. For a person with red-green CVD:
- The figure dots and background dots appear to have the same colour and brightness
- The number becomes invisible (or a different number becomes visible instead)
Types of Plates
| Plate Type | What Normal Vision Sees | What CVD Sees |
|---|---|---|
| Transformation | Number A | Number B |
| Vanishing digit | A number | Nothing (blank) |
| Hidden digit | Nothing | A number |
| Classification | One set of digits | A different set (distinguishes protan from deutan) |
Control plates — which everyone should be able to read — are included at the start to verify the test is being administered and interpreted correctly.
Conventional 38-, 24-, and 14-plate editions
The published clinical Ishihara test exists in several editions:
- 38-plate edition — the full diagnostic set; includes all plate types and classification plates
- 24-plate edition — the most commonly used clinical version
- 14-plate edition — a quick screening version for time-limited settings
ColorVision does not reproduce one of those editions. Its digit plate activity uses 24 original, browser-generated plates to demonstrate the same broad colour-separation task. It has not been validated against the published plate books and does not cover or score their diagnostic categories.
What does the conventional Ishihara test screen for?
The Ishihara test is specifically designed to detect red-green colour vision deficiency (protanopia, protanomaly, deuteranopia, and deuteranomaly). It is not designed to detect:
- Tritanopia (blue-yellow deficiency)
- Achromatopsia (complete colour blindness)
- Acquired colour vision changes from disease or medication
An eye-care professional can select additional validated tests when a broader assessment is needed. A browser hue-order activity can illustrate a different task format, but it is not a substitute for that assessment.
How to Interpret Results
Each published clinical edition has its own administration and scoring instructions. Its thresholds should not be transferred to a different collection of plates. ColorVision reports how many responses matched its own original figures and uses cautious prompts to repeat or seek professional advice; it does not issue a clinical pass, type, or severity.
Limitations of Online Ishihara Tests
Ishihara-style browser activities can provide educational feedback but have inherent limitations:
- Screen calibration — different monitors display colours differently; an uncalibrated monitor may affect results
- Ambient lighting — bright room light, sun glare, or blue-light filters distort colour perception
- Screen type — OLED vs LCD vs CRT displays render colours differently
- No colour management — printed plates use precisely controlled Munsell colour inks; digital screens cannot perfectly replicate this
For these reasons, online tests are screening tools, not clinical diagnostic tools. A positive result (indicating possible CVD) should be followed up with a formal clinical test.
Frequently Asked Questions
Who invented the Ishihara test? Dr. Shinobu Ishihara, a Japanese Army ophthalmologist, who published the test in 1917 while at the Tokyo Army Medical School.
Is the Ishihara test accurate? Performance depends on the edition, administration, population, and scoring rule. Evidence about a validated printed edition administered under controlled conditions does not establish the accuracy of a browser-generated activity such as ColorVision’s.
How long does the Ishihara test take? In clinical settings with printed plates, approximately 5 minutes. ColorVision’s separate, original 24-plate browser activity typically takes 3–5 minutes.
Can an online plate activity determine severity? No. ColorVision’s original plates do not determine clinical severity. A professional assessment uses validated materials and an interpretation appropriate to the person’s purpose and history.
Evidence & sources
These sources provide background on colour vision deficiency and conventional clinical testing. ColorVision’s browser-based activities are educational screens, not clinical instruments.
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