The Ishihara test is a colour vision screening tool that uses pseudoisochromatic plates made of coloured dots to detect red-green colour deficiencies. It is widely used in clinical and occupational settings.
How the Test Works
Each plate contains a number or path formed by dots in one colour range, set against a background of dots in another range. People with normal colour vision can usually identify the figure, while those with specific colour deficiencies may not see it or see a different pattern.
- Administered at a standard reading distance under appropriate lighting
- Suitable for literate children and adults; symbol plates are available for young children
- Quick to perform, often using a subset of plates for screening
- Helps distinguish normal from abnormal colour vision but not all subtle types
Clinical Use
Ishihara testing primarily detects congenital red-green colour deficiencies and is less sensitive to blue-yellow or acquired defects. Abnormal results are often followed by more detailed colour vision assessment when needed.
- Used for occupational screening where accurate colour discrimination is important
- Results guide counselling about job choices and safety considerations
- Repeated testing can help confirm borderline findings
- Test conditions must be standardised to avoid misclassification
