American Board of Ophthalmology (ABO) Practice Exam

For lensometers to give accurate readings, what must be properly calibrated?

1. The eyepiece

2. The lens holder

3. The power switch

4. The focus knob

The correct answer is: The eyepiece

For lensometers to provide accurate readings, it is essential that the eyepiece is properly calibrated. The eyepiece allows the operator to view and read the power of the lenses being tested, and any miscalibration can lead to incorrect measurements. When the eyepiece is correctly calibrated, it ensures that the readings reflect the true optical power of the lens, allowing for precise prescription verification. In a lensometer, calibration of the eyepiece aligns the viewing apparatus with the optical axis of the instrument. Proper calibration ensures that the lens measurements account for any variations in lens design or manufacturing that may affect how power is determined and viewed through the eyepiece. While other components like the lens holder, focus knob, and power switch play important roles in the overall function of the lensometer, the most critical factor impacting the accuracy of the readings relates specifically to the calibration of the eyepiece. A well-calibrated eyepiece directly affects the precision and reliability of the lens power measurements obtained from the device.