Introduction To Vision Rehabilitation Practice Test

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

0.75 1.25 1.75 1.50

Correct Answer:

1.50

Explanation:

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.

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