Your patient has 10/25 vision at 10 feet. What is the JND?

Your patient has 10/25 vision at 10 feet. What is the JND?

• A. 0.75
• B. 0.50
• C. 0.25
• D. 1.00

Answer: (C)

The key idea is the smallest change in visual acuity that a person can reliably notice, called the Just Noticeable Difference (JND). In distance acuity testing, a commonly used threshold for a noticeable change is about 0.25 logMAR, which corresponds to roughly two to three lines on a standard chart. Your patient’s 10/25 vision corresponds to about 0.40 logMAR. A change of about 0.25 logMAR from that baseline would be the smallest difference most people can detect, making 0.25 the appropriate JND. The larger values would reflect bigger, more easily detected changes, while smaller values would be harder to notice reliably.

The key idea is the smallest change in visual acuity that a person can reliably notice, called the Just Noticeable Difference (JND). In distance acuity testing, a commonly used threshold for a noticeable change is about 0.25 logMAR, which corresponds to roughly two to three lines on a standard chart. Your patient’s 10/25 vision corresponds to about 0.40 logMAR. A change of about 0.25 logMAR from that baseline would be the smallest difference most people can detect, making 0.25 the appropriate JND. The larger values would reflect bigger, more easily detected changes, while smaller values would be harder to notice reliably.