This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Ophthalmology
Isochromatic chas are used for: March 2008 
Select and explain. 
A. Contrast sensitivity, B. Testing colour vision, C. Visual fields chaing, D. Visual acuity testing
B: Testing colour vision
Answer: B: Testing colour vision 
Explanation: Ans. B: Testing colour vision Isochromatic chas/Japanese Ishihara chas is used for testing colour vision and it largely identifies red-green anomalies. The American Hardy-Rand-Ritler (H-R-R) test identifies blue-yellow anomalies.