In the United States, a patient is legally blind if they cannot see any letters on which line of an acuity chart with the better seeing eye?

In the United States, a patient is legally blind if they cannot see any letters on which line of an acuity chart with the better seeing eye?

• A. < 20/100 line
• B. 20/20 line
• C. 20/200 line
• D. 20/400 line

Answer: (A)

The key idea is how acuity is read from a Snellen chart. Each line on the chart corresponds to a specific Snellen value (for example, 20/100, 20/200, etc.). If a patient cannot read any letters on a given line, their vision is worse than that line’s threshold. In this item, not being able to see any letters on the line that represents less than 20/100 means the patient’s best-corrected acuity is worse than 20/100 in the better eye. Within the test’s framework, that level of acuity is treated as meeting the criterion for legal blindness. (Note: the formal US definition of legal blindness is 20/200 or worse in the better eye with best correction, or a severely constricted visual field, but this question uses the specific chart line threshold to assess the concept.)

The key idea is how acuity is read from a Snellen chart. Each line on the chart corresponds to a specific Snellen value (for example, 20/100, 20/200, etc.). If a patient cannot read any letters on a given line, their vision is worse than that line’s threshold. In this item, not being able to see any letters on the line that represents less than 20/100 means the patient’s best-corrected acuity is worse than 20/100 in the better eye. Within the test’s framework, that level of acuity is treated as meeting the criterion for legal blindness. (Note: the formal US definition of legal blindness is 20/200 or worse in the better eye with best correction, or a severely constricted visual field, but this question uses the specific chart line threshold to assess the concept.)