Colour Vision Testing: Ishihara Scoring, Other Tests and Job Rules
Last updated: October 2026
How to perform and score the Ishihara test, which tests to add, and how colour vision affects driving and job medicals.
Ishihara: how to test
- Use good daylight or a daylight lamp, hold the book at about 75 cm, tilt it at right angles to the line of sight, and allow no more than 3 seconds per plate.
- Test each eye separately (acquired defects can be one-sided), with near correction if needed.
- Plate 1 is a demonstration plate that everyone, including people with colour deficiency, should read; failure suggests poor vision or malingering.
Scoring
| Edition | Screening plates | Normal | Red-green deficiency |
|---|---|---|---|
| 38-plate | 1–21 | 17 or more read correctly | 13 or fewer read correctly |
| 24-plate | 1–15 | 13 or more read correctly | 9 or fewer read correctly |
| 14-plate (concise) | 1–11 | 10 or more read correctly | 7 or fewer read correctly |
Scores between these limits are borderline: retest and use a second test. Classification plates (22–25 in the 38-plate edition) separate protan from deutan defects and grade them as mild or strong. Ishihara does not test blue-yellow (tritan) defects.
Other tests
| Test | Use |
|---|---|
| HRR (Hardy–Rand–Rittler) plates | Detects and grades red-green and blue-yellow defects; useful for acquired disease |
| Farnsworth D-15 | Separates mild from moderate–severe defects; used in occupational testing |
| Farnsworth–Munsell 100 hue | Detailed grading; research and acquired disease |
| Anomaloscope (Nagel) | Gold standard for classifying red-green defects |
| Lantern tests (Holmes-Wright, Edridge-Green) | Practical signal-light tests for railways, defence, aviation and shipping |
| City University test | Simple test for tritan and acquired defects |
Congenital versus acquired defects
- Congenital: both eyes equally, stable, usually red-green, X-linked (about 8% of men and 0.5% of women of European ancestry; somewhat lower in Indian studies).
- Acquired: may differ between eyes, may change, often blue-yellow in early macular disease and glaucoma, red-green in optic neuropathy (optic neuritis, ethambutol, compressive lesions). Test colour vision when starting ethambutol and at follow-up.
Occupational relevance (India)
- Driving: only severe colour blindness bars a licence (GSR 401(E), 2020).
- Railways: normal colour vision is required for the A and B medical categories.
- Defence and aviation: colour perception grades (CP-I to CP-III) and lantern tests are specified in each notification.
- No treatment, tinted lens or app corrects congenital colour deficiency for these tests; tinted lenses can mislead examiners and are not accepted.
Related: vision standards for driving and jobs, colour vision deficiency (Gujarati, for patients).
Key sources
- Ishihara S. Tests for Colour-Deficiency, 38 Plates Edition. Kanehara Trading Inc. (instructions for use)
- Birch J. Diagnosis of Defective Colour Vision. 2nd ed. Butterworth-Heinemann; 2001
- Ministry of Road Transport and Highways. GSR 401(E), 24 June 2020
📘 Want more exam-ready material? See Most Commons in Ophthalmology on Kindle, or browse all my books.
Looking for an eye specialist in Ahmedabad? Learn about our Eye Department or book a consultation with Dr. Dhaval Patel.