NOCE Dispensing and Fitting Procedures 4

Question 1

A patient's PD is 63 mm and the frame's distance between lenses (DBL) is 18 mm with each eye size of 50 mm. What is the monocular decentration needed per lens?

Accepted Answer

1.5 mm per lens

Answer

The geometric center of each lens is at 50/2 + 18/2 = 34 mm from the center; for a 63 mm PD the half-PD is 31.5 mm, giving 34 - 31.5 = 2.5 mm total, or 1.5 mm per lens inward (monocular decentration = (ED/2 + DBL/2) - half-PD = 25+9=34 - 31.5 = 2.5 mm total / this is the binocular decentration; monocular = 1.5 mm inward per lens).

Question 2

Which instrument is used to locate and mark the optical center of a finished lens before insertion into the frame?

Accepted Answer

Lensometer (focimeter)

Answer

The lensometer identifies and marks the optical center (and other reference points) of a finished ophthalmic lens.

Question 3

A patient with a prescription of +6.00 DS would benefit most from which type of frame to minimize magnification?

Accepted Answer

Small frame with aspheric high-index lenses

Answer

Aspheric designs flatten lens curves to reduce magnification, and a smaller eye size reduces center thickness in high plus prescriptions.

Question 4

When verifying a finished bifocal, what is the ANSI Z80.1 tolerance for segment height difference between the two lenses?

Accepted Answer

1.0 mm

Answer

ANSI Z80.1 permits a maximum of 1.0 mm difference in segment height between the right and left lenses of a finished bifocal.

Question 5

A child's frame sits very close to the eyelashes, causing lens contact. The BEST adjustment is to:

Accepted Answer

Increase the vertex distance by opening the nose pads outward

Answer

Increasing vertex distance by adjusting nose pads to widen their spread moves the frame away from the face, clearing the eyelashes.

NOCE - National Opticianry Competency Examination Practice Test

NOCE - National Opticianry Competency Examination Practice Test

NOCE Dispensing and Fitting Procedures 4