NOCE Optical Instrumentation Use 4

Question 1

When using a lensometer on a high-minus lens with significant spherical aberration, what technique improves measurement accuracy?

Accepted Answer

Stop down the aperture using the iris diaphragm

Answer

Stopping down the aperture (using the iris diaphragm) reduces aberrations and makes the target appear sharper for high-power lenses.

Question 2

If a keratometer measures 41.00 D @ 180 / 43.50 D @ 090, what is the simulated K (SimK) or average K?

Accepted Answer

42.25 D

Answer

The average K (SimK) is the mean of the two principal meridian readings: (41.00 + 43.50) / 2 = 42.25 D.

Question 3

When fitting a rigid gas-permeable (RGP) lens, a fluorescein pattern that shows pooling centrally and bearing peripherally (steep fit) would require what adjustment to the base curve?

Accepted Answer

Flatten the base curve

Answer

Central pooling with peripheral bearing indicates the lens is too steep; flattening the base curve improves the fit.

Question 4

The non-contact tonometer (NCT) measures intraocular pressure by detecting what?

Accepted Answer

The time or force needed to applanate the cornea with an air puff

Answer

The NCT uses a calibrated puff of air and detects the time or force required to momentarily flatten (applanate) the cornea, correlating this to IOP.

Question 5

A distometer is used in spectacle dispensing to measure which distance?

Accepted Answer

Vertex distance from the back lens surface to the cornea

Answer

A distometer measures the vertex distance — the space between the back surface of the spectacle lens and the front of the cornea.

NOCE - National Opticianry Competency Examination Practice Test

NOCE - National Opticianry Competency Examination Practice Test

NOCE Optical Instrumentation Use 4