Certified Paraoptometric (CPO) Practice Exam 2025

What instrument is commonly used to verify a spectacle prescription?

1. Phoropter

2. Lensometer

3. Retinoscope

4. Ocular tonometer

The correct answer is: Lensometer

The lensometer is the correct instrument for verifying a spectacle prescription. It is designed specifically to measure the optical power of lenses in spectacles. By placing the lens in the device, the lensometer allows the technician or optometrist to read the prescription etched or printed on the lens. It accurately determines factors such as sphere, cylinder, and axis, ensuring that the glasses match the optical prescription provided by the eye care professional. While a phoropter is used during an eye exam to determine a patient’s prescription through subjective refraction, it doesn’t verify the prescription after the lenses are made. A retinoscope is employed to estimate a refractive error and assist in determining a prescription during an examination, but it also does not function to verify the final spectacle prescription. Lastly, an ocular tonometer is used to measure intraocular pressure, which is unrelated to verifying spectacle prescriptions. Thus, these other instruments have their own specific purposes within optometry but do not serve the same role as the lensometer in verifying spectacle prescriptions.