13/03/2026
Ishihara Test – Purpose and How It Works
1️⃣ What is the Ishihara Test?
The Ishihara test is a simple eye test used to detect color vision deficiency (color blindness). It mainly checks problems in distinguishing red and green colors, which is the most common type of color blindness.
It was developed by the Japanese ophthalmologist Shinobu Ishihara in 1917.
🎯 Purpose of Ishihara Test
The test is used to:
Detect red-green color blindness
Screen patients during eye examination
Check visual fitness for certain jobs (driver, pilot, military, etc.)
Identify congenital or acquired color vision defects
⚙️ How the Ishihara Test Works
The test uses special plates called pseudo-isochromatic plates.
Each plate contains:
Many colored dots
A number or pattern hidden inside the dots
Procedure
The patient sits at about 75 cm distance from the chart.
Plates are shown one by one for about 3 seconds.
The patient is asked to read the number seen in the plate.
Interpretation
Normal color vision: Patient reads the correct number.
Red-green deficiency: Patient cannot see the number or reads a different number.
Example:
Normal person may see 12
Color-deficient person may see nothing or another number
📊 Types of Ishihara Plates
Transformation plates – number seen differently by normal and color-deficient people
Vanishing plates – number visible to normal but not to color-blind person
Hidden plates – number seen only by color-deficient people
Diagnostic plates – help determine the type of defect
🩺 Clinical Importance
The Ishihara test is widely used in:
Optometry
Ophthalmology clinics
School screening
Medical examinations for jobs
It is one of the most common and reliable screening tests for color blindness.
