NOCE Optical Instrumentation Usage 2

Question 1

When using a lensometer to measure a bifocal lens, where should the segment be positioned relative to the lens stop?

Accepted Answer

Below the lens stop

Answer

The bifocal segment should be positioned below the lens stop so the distance portion is measured first through the aperture.

Question 2

A keratometer reading of 44.00 @ 90 / 46.00 @ 180 indicates which type of corneal astigmatism?

Accepted Answer

Against-the-rule astigmatism

Answer

Against-the-rule astigmatism occurs when the flattest meridian is vertical (90°) and the steepest is horizontal (180°).

Question 3

Which instrument is specifically used to measure the back vertex distance of a spectacle lens?

Accepted Answer

Distometer

Answer

A distometer (also called a vertex distance gauge) measures the distance from the back surface of the lens to the cornea.

Question 4

On a manual lensometer, what does a clear, sharp image of the target mires indicate?

Accepted Answer

The sphere power has been neutralized

Answer

When the target mires appear clear and sharp in the lensometer eyepiece, the sphere power of the lens has been neutralized.

Question 5

A Geneva lens measure is used on a plus lens and reads +3.00 on the front surface and -1.00 on the back surface. What is the approximate lens power?

Accepted Answer

+2.00 D

Answer

Lens power approximation by lens measure is calculated by adding front and back surface powers: +3.00 + (-1.00) = +2.00 D.

NOCE - National Opticianry Competency Examination Practice Test