In Snellen vision testing, how far should a patient stand from the eye chart?

In Snellen vision testing, how far should a patient stand from the eye chart?

• A. Stand 20 feet away from the eye chart
• B. Stand 10 feet away from the eye chart
• C. Stand 30 feet away from the eye chart
• D. Stand 15 feet away from the eye chart

Answer: (A)

In Snellen vision testing, the distance is standardized so the letters on the chart subtend a consistent angle at the eye. The accepted testing distance is 20 feet, so a person with normal vision should be able to read at 20 feet what the chart indicates for that line. This standard distance lets clinicians compare results reliably across patients and over time. In metric practice, 6 meters serves the same purpose. Testing from other distances would misrepresent true acuity: reading from a shorter distance could make vision appear better than it is, while reading from a longer distance would make it seem worse. Therefore, 20 feet is the appropriate testing distance.

In Snellen vision testing, the distance is standardized so the letters on the chart subtend a consistent angle at the eye. The accepted testing distance is 20 feet, so a person with normal vision should be able to read at 20 feet what the chart indicates for that line. This standard distance lets clinicians compare results reliably across patients and over time. In metric practice, 6 meters serves the same purpose. Testing from other distances would misrepresent true acuity: reading from a shorter distance could make vision appear better than it is, while reading from a longer distance would make it seem worse. Therefore, 20 feet is the appropriate testing distance.