If the lensometer reading is +1.00 but the calibration reading for sharp focus is +0.25, how would you record the neutralized reading?

If the lensometer reading is +1.00 but the calibration reading for sharp focus is +0.25, how would you record the neutralized reading?

• A. +0.75
• B. +1.00
• C. +0.25
• D. +1.75

Answer: (A)

In lensometry, the calibration reading for sharp focus represents an offset of the instrument that must be removed from the measured lens power to reveal the true, neutralized prescription. To get that neutralized value, subtract the calibration offset from the lensometer reading. Here, the lensometer shows +1.00 and the calibration for sharp focus is +0.25. So the neutralized reading is +1.00 − +0.25 = +0.75. You would record +0.75. This approach ensures the final power you document reflects the lens’s actual power, independent of the instrument’s calibration state. Recording +1.00 would ignore the calibration offset, recording +0.25 would reflect only the calibration baseline, and adding instead of subtracting would overcompensate.

In lensometry, the calibration reading for sharp focus represents an offset of the instrument that must be removed from the measured lens power to reveal the true, neutralized prescription. To get that neutralized value, subtract the calibration offset from the lensometer reading.

Here, the lensometer shows +1.00 and the calibration for sharp focus is +0.25. So the neutralized reading is +1.00 − +0.25 = +0.75. You would record +0.75.

This approach ensures the final power you document reflects the lens’s actual power, independent of the instrument’s calibration state. Recording +1.00 would ignore the calibration offset, recording +0.25 would reflect only the calibration baseline, and adding instead of subtracting would overcompensate.