Using the minus lens method, a patient first experiences sustained blur at -3.00D. What is their amplitude of accommodation?

Using the minus lens method, a patient first experiences sustained blur at -3.00D. What is their amplitude of accommodation?

• A. 2.50D
• B. 5.50D
• C. 3.00D
• D. 4.00D

Answer: (B)

In the minus lens method, you keep the target at a fixed near distance and add minus lenses until sustained blur appears. The eye must accommodate for both the fixed distance to the target and the additional demand from the minus lens. The amplitude of accommodation is the total amount the eye can accommodate, which equals the near demand of the target plus the extra demand created by the minus lens at blur. If the fixed target is at 40 cm, the accommodative demand is 1/0.40 = 2.50 diopters. Blur occurs with a minus lens of 3.00 D, so the total required accommodation is 2.50 + 3.00 = 5.50 D. Therefore, the amplitude of accommodation is 5.50 diopters.

In the minus lens method, you keep the target at a fixed near distance and add minus lenses until sustained blur appears. The eye must accommodate for both the fixed distance to the target and the additional demand from the minus lens. The amplitude of accommodation is the total amount the eye can accommodate, which equals the near demand of the target plus the extra demand created by the minus lens at blur.

If the fixed target is at 40 cm, the accommodative demand is 1/0.40 = 2.50 diopters. Blur occurs with a minus lens of 3.00 D, so the total required accommodation is 2.50 + 3.00 = 5.50 D. Therefore, the amplitude of accommodation is 5.50 diopters.