In the minus lens test, the correction added to account for the working distance is which value?

In the minus lens test, the correction added to account for the working distance is which value?

• A. +0.50D
• B. +1.50D
• C. +2.50D
• D. +3.50D

Answer: (C)

In the minus lens test, you add a correction to account for how far the eye is from the testing instrument. This working-distance correction is the reciprocal of that distance in meters, expressed in diopters. If the working distance is 40 cm (0.40 m), the correction is 1/0.40 = +2.50 D. So the adjustment used here is +2.50 diopters. Other numbers would correspond to different working distances (for example, 50 cm would be +2.00 D, 33 cm would be +3.00 D), but the standard setup uses 40 cm, making +2.50 D the appropriate value.

In the minus lens test, you add a correction to account for how far the eye is from the testing instrument. This working-distance correction is the reciprocal of that distance in meters, expressed in diopters. If the working distance is 40 cm (0.40 m), the correction is 1/0.40 = +2.50 D. So the adjustment used here is +2.50 diopters. Other numbers would correspond to different working distances (for example, 50 cm would be +2.00 D, 33 cm would be +3.00 D), but the standard setup uses 40 cm, making +2.50 D the appropriate value.