What is the JND of a 76-year-old patient with AMD and acuities of 10/200 in each eye?

• A. 1.00
• B. 2.00
• C. 3.00
• D. 4.00

Answer: (B)

The key idea is that the JND is the smallest change in acuity a person can reliably notice. In someone with AMD and very poor acuity (10/200 in each eye), central vision is severely damaged and contrast sensitivity is reduced, so their perceptual threshold for detecting changes is larger. In this level of impairment, a JND around 2.00 units on the common low-vision acuity scale reflects the reality that only relatively larger improvements are detectable. Smaller values (like 1.00) would imply finer discrimination than typically possible with this degree of vision loss, while larger values (3.00 or 4.00) would indicate an even bigger threshold than usually observed. So 2.00 best matches the expected perceptual threshold for this level of AMD-related vision.