NOCE Optical Instrumentation Use 5

Question 1

When a lensometer target shows two distinct sets of lines perpendicular to each other that cannot both be brought into focus simultaneously, this indicates the lens has:

Accepted Answer

Cylinder (astigmatic) power

Answer

Inability to focus two perpendicular line sets simultaneously in a lensometer indicates cylindrical (astigmatic) power in the lens.

Question 2

On a Bausch & Lomb keratometer (one-position instrument), mire doubling is achieved by which mechanism?

Accepted Answer

Adjusting internal prisms or drums

Answer

The B&L keratometer uses internal prisms (drums) to double the mire images, allowing measurement in a single instrument position.

Question 3

When verifying the optical center placement of a finished spectacle lens using a lensometer, the ink dots should be placed while the lens is:

Accepted Answer

Placed with the front surface facing the instrument

Answer

The lens is placed in the lensometer with the front surface facing the instrument (convex side toward the lens stop) for standard measurement.

Question 4

A contact lens projection magnifier (shadowgraph) is used to measure which contact lens parameter by projecting an enlarged image?

Accepted Answer

Diameter and surface quality

Answer

A shadowgraph projects an enlarged shadow image of a contact lens to measure its overall diameter and inspect surface quality or edge defects.

Question 5

When using a PD ruler to measure monocular PDs, the examiner should close which of their own eyes to eliminate parallax error?

Accepted Answer

The eye opposite to the patient's eye being measured

Answer

To eliminate parallax, the examiner closes the eye opposite to the patient's eye being measured, so their open eye is aligned over the measurement point.

NOCE - National Opticianry Competency Examination Practice Test

NOCE - National Opticianry Competency Examination Practice Test

NOCE Optical Instrumentation Use 5