About the Ishihara Test
The gold standard for color vision screening since 1917. Understand the science, methodology, and limitations of this widely-used diagnostic tool.
What Is the Ishihara Test?
The Ishihara color perception test is the most widely used screening test for red-green color vision deficiencies worldwide. It was designed by Dr. Shinobu Ishihara, a professor at the University of Tokyo, and first published in 1917.
The test consists of a series of circular plates (called "Ishihara plates") composed of colored dots arranged in seemingly random patterns. Within each plate, dots of a specific color form a number or pathway that is visible to people with normal color vision but partially or completely invisible to those with color vision deficiency.
The original test book contains 38 plates and remains the standard format used by eye care professionals today. Our online version replicates this 38-plate format using programmatically generated Ishihara-style plates for educational screening purposes.
How the Plates Work
Demonstration Plates
The first and last plates contain numbers visible to everyone, regardless of color vision. These confirm the subject understands the task and can see the plate format. Our test uses plates 1 and 38 as demonstration plates.
Transformation Plates
These plates show one number to people with normal vision and a different number to those with color vision deficiency. For example, a person with normal vision might see "29" while someone with red-green deficiency sees "70." This is possible because the number-forming dots and background dots fall along specific color confusion lines.
Vanishing Plates
These plates contain numbers visible only to people with normal color vision. People with color vision deficiency cannot distinguish the number from the background and see nothing (or a random pattern). These are the most straightforward diagnostic plates.
Hidden Digit Plates
The reverse of vanishing plates: these contain numbers that are only visible to people with color vision deficiency. A person with normal vision sees nothing, while someone with red-green deficiency clearly sees a number. These confirm a positive screening result.
Diagnostic Plates
These specialized plates help distinguish between protan (red) and deutan (green) deficiency. They contain two-digit numbers where each digit lies along different confusion lines. A person with protanopia might read only one digit, while a person with deuteranopia reads a different one.
What the Test Measures
The Ishihara test is specifically designed to detect red-green color vision deficiencies (protanopia, protanomaly, deuteranopia, and deuteranomaly). It can:
Can Detect
- Presence of red-green color blindness
- Differentiation between protan and deutan types
- Approximate severity (mild, moderate, severe)
- Some tritan (blue-yellow) deficiency indicators
Cannot Determine
- Precise severity measurement (use anomaloscope)
- Acquired vs inherited color blindness
- Complete achromatopsia diagnosis
- Occupational fitness (use Farnsworth D-15)
Limitations & Disclaimers
This online test is not a medical diagnosis. While it uses the same methodology as the clinical Ishihara test, several factors make online screening less precise than a professional examination:
Screen Calibration
Every monitor displays colors differently. Without calibration, the colors you see may not match the intended test colors.
Ambient Lighting
Room lighting affects how colors appear on screen. Clinical testing uses controlled, standardized lighting (D65 illuminant).
Display Technology
LCD, OLED, and AMOLED screens have different color gamuts and contrast ratios, which can affect plate visibility.
Algorithmic Generation
Our plates are programmatically generated, not photographed from the original Ishihara book. While using the same color science principles, they are approximations.
When to See a Professional
You should consult an eye care professional (optometrist or ophthalmologist) if:
This test indicates possible color vision deficiency
A professional can confirm the diagnosis with calibrated, standardized equipment and provide a definitive classification.
You've noticed recent changes in your color perception
Acquired color blindness can indicate underlying conditions such as diabetes, glaucoma, macular degeneration, or medication side effects.
You need certification for employment or licensing
Many professions (aviation, maritime, military, electrical work) require certified color vision testing that only a clinical exam can provide.
Your child is starting school
Early detection helps educators provide appropriate accommodations. Color-coded learning materials are common in early education.
Take the Free Test
Ready to assess your color vision? Our free 38-plate test takes under 2 minutes.
Start Free Test