NOCE Ophthalmic Optics and Formulas 5

Question 1

The standard fitting height for a flat-top 28 bifocal segment is measured from:

Accepted Answer

The lowest point of the pupil to the top of the bifocal segment

Answer

Segment height is measured from the lowest limbal margin of the pupil down to the top of the bifocal segment.

Question 2

Spectacle magnification (SM) is the product of which two factors?

Accepted Answer

Power factor and shape factor

Answer

SM = Power Factor × Shape Factor; power factor depends on back vertex power and vertex distance, shape factor on front curve and thickness.

Question 3

A near addition of +2.50 D allows a patient to focus at what working distance?

Accepted Answer

40 cm

Answer

Working distance = 1 / add power = 1 / 2.50 = 0.40 m = 40 cm.

Question 4

Monocular PD for bifocal segment centration should be measured with the patient:

Accepted Answer

Looking straight ahead at distance fixation

Answer

Distance monocular PD is measured with the patient looking at a distance target, ensuring proper optical center placement for the distance portion.

Question 5

Image jump at the top of a bifocal segment is determined by:

Accepted Answer

The add power multiplied by the distance from the segment top to the segment's optical center

Answer

Image jump = add power × distance from segment top to segment optical center; for flat-tops the OC is below the top, causing jump.

NOCE - National Opticianry Competency Examination Practice Test