This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Miscellaneous, Subject name: Ophthalmology
Distance of patient w hile reading Snellen chart is 
Select and explain. 
A. 6 feet, B. 25 ems, C. 6 meters, D. 25 feet
C: 6 meters
Answer: C: 6 meters 
Explanation: (C) 6 meters # SNELLEN CHART is an eye chart that can be used to measure visual acuity.> Visual acuity = Distance at which test is made / distance at which the smallest optotype identified subtends an angle of 5 arcminutes.> In the most familiar acuity test, a Snellen chart is placed at a standard distance: 6 metres (or 20 ft). At this distance, the symbols on the line representing ""normal"" acuity subtend an angle of five minutes of arc, and the thickness of the lines and of the spaces between the lines subtends one minute of arc. This line, designated 6/6 (or 20/20), is the smallest line that a person with normal acuity can read at a distance of 6 metres (20 ft).