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
Ishihara chas are used in diagnosis of which of the following? 
Select and explain. 
A. Myopia, B. Hypermetropia, C. Colour blindness, D. None of the above
C: Colour blindness
Answer: C: Colour blindness 
Explanation: The most common test for color blindness uses the Ishihara chas, which are plates containing figures made up of colored spots on a background of similarly shaped colored spots. Ref: Ganong's Review of Medical Physiology 23rd edition, Chapter 12.