Blindness is defined as a visual acuity of less than or equal to which value?

• A. 20/200
• B. 20/20
• C. 2/20
• D. 2/200

Answer: (A)

Understanding how visual acuity is expressed helps here. A Snellen fraction like 20/200 compares what a person can see at testing distance to what a person with normal vision can see at a greater distance. The top number is the testing distance (20 feet), and the bottom number is the distance at which a person with normal vision could read the same line. So 20/200 means you can read at 20 feet what a person with normal vision could read from 200 feet—very limited vision.

The commonly used threshold for legal blindness is 20/200 or worse in the better eye, even with the best correction. That’s why 20/200 is the correct standard. The other values describe different, typically less severe levels of acuity (20/20 is normal; 2/20 or 2/200 would indicate even poorer acuity, but they are not the standard benchmark for blindness).