True or False: JND is fluid, meaning it will change as the refraction progresses.

• A. False
• B. True
• C. It can vary
• D. Not necessarily true

Answer: (B)

Just noticeable difference is the smallest change in a stimulus that a person can reliably detect. In vision, that threshold isn’t fixed for an individual. It shifts with the eye’s current state and viewing conditions—accommodation, pupil size, illumination, contrast, and overall retinal image quality all influence how noticeable a change in lens power will be. As you move through the refraction process, these factors change, so the amount of diopters needed to notice a difference also changes. That makes JND fluid during refraction, so the statement is true.