If JND is 0.75 D, what is the cylinder power for a patient with 10/100 vision?

If JND is 0.75 D, what is the cylinder power for a patient with 10/100 vision?

• A. 0.75
• B. 1.25
• C. 1.75
• D. 1.50

Answer: (D)

The main idea is that JND is the smallest change in refractive power a patient can notice, and in low vision the amount of change needed to be noticed is larger. For someone with only 10/100 vision, their perceptual threshold for changes in cylinder power is roughly higher, often about twice the standard JND. With a JND of 0.75 D, the change in cylinder power that is likely to be perceived falls around 1.50 D. Therefore, the cylinder power around 1.50 D is the best choice because it corresponds to a perceptible adjustment given the patient’s reduced acuity. The other values represent smaller or irregular increments that would likely go unnoticed in this level of vision.

The main idea is that JND is the smallest change in refractive power a patient can notice, and in low vision the amount of change needed to be noticed is larger. For someone with only 10/100 vision, their perceptual threshold for changes in cylinder power is roughly higher, often about twice the standard JND. With a JND of 0.75 D, the change in cylinder power that is likely to be perceived falls around 1.50 D. Therefore, the cylinder power around 1.50 D is the best choice because it corresponds to a perceptible adjustment given the patient’s reduced acuity. The other values represent smaller or irregular increments that would likely go unnoticed in this level of vision.