## Core Concept
The Snellen chart is a tool used for measuring visual acuity, which is the sharpness and clarity of vision. It consists of lines of letters that decrease in size as you move down the chart. The standard distance for reading the Snellen chart is crucial for accurate measurement of visual acuity.

## Why the Correct Answer is Right
The correct distance for a patient to read the Snellen chart is 6 meters (or 20 feet), which allows for the measurement of visual acuity under standard conditions. This distance enables the assessment of the patient's ability to see objects clearly at a normal reading distance. The Snellen chart is designed so that a person with normal vision can read the letters on the 6/6 line (or 20/20 line) from a distance of 6 meters.

## Why Each Wrong Option is Incorrect
- **Option A:** 3 meters is half the standard distance and would not provide an accurate measurement of visual acuity according to the standard Snellen chart protocol.
- **Option B:** 5 meters is close but not the standard distance used for reading the Snellen chart; it would slightly alter the visual acuity measurement.
- **Option D:** 10 meters is farther than the standard distance and would not be a practical or commonly used distance for assessing visual acuity with a Snellen chart.

## Clinical Pearl / High-Yield Fact
A key point to remember is that the Snellen chart's 6/6 vision (or 20/20 vision) signifies normal visual acuity. This measurement is taken from a distance of 6 meters, making it a critical piece of information for ophthalmology and general medical practice.

## Correct Answer: C. 6 meters.