This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Errors of Refraction, Subject name: Ophthalmology
Snellen's chart is used to test? 
Select and explain. 
A. Visual acuity, B. Contrast sensitivity, C. Visual fields, D. Colour vision
A: Visual acuity
Answer: A: Visual acuity 
Explanation: Ans. is 'a' i.e., Visual acuity * Visual acuity of a eye is its ability to discriminate between two points, i.e. measure of the spatial resolution of the eye. One's visual acuity is an indication of the clarity or clearness of one's vision. It is a measurement of how well a person sees. Visual acuity is most commonly measured by Snellen's visual acuity chart.