CPO Lensometry and Spectacle Lens Verification

Question 1

What instrument is used to verify the optical power of a finished spectacle lens?

Accepted Answer

Lensometer (lensmeter)

Answer

The lensometer (also called a lensmeter or focimeter) is the standard instrument used to measure and verify the refractive power of spectacle lenses after fabrication.

Question 2

On a manual lensometer, focusing the sphere mire target gives you:

Accepted Answer

The sphere power

Answer

When the sphere (rotationally symmetric) mire is focused sharply, you read the sphere power directly from the power drum.

Question 3

On a manual lensometer with crossed-line mires, when one set of lines focuses sharply but the other does not at the same drum setting, this indicates:

Accepted Answer

A toric (spherocylindrical) lens

Answer

When the two sets of mire lines require different drum settings to focus, the lens has cylindrical power, making it a toric or spherocylindrical lens.

Question 4

By ANSI/ISO convention, the axis of a cylindrical spectacle lens is measured:

Accepted Answer

1° to 180° counterclockwise

Answer

By ANSI/ISO convention, spectacle lens axis is measured from 1° to 180° counterclockwise when viewing the lens from the front.

Question 5

Before measuring any lens on a lensometer, the first step the technician should perform is:

Accepted Answer

Zero-calibrate the lensometer eyepiece and power drum

Answer

Calibrating the lensometer by zeroing the eyepiece and confirming zero power with no lens in place ensures all subsequent measurements are accurate.

(CPO) Certified Paraoptometric Practice Test

(CPO) Certified Paraoptometric Practice Test

CPO Lensometry and Spectacle Lens Verification