NOCE Ophthalmic Optics and Lenses 4

Question 1

A progressive addition lens (PAL) fitting cross is placed at what anatomical landmark?

Accepted Answer

Pupil center

Answer

The fitting cross of a PAL is aligned with the pupil center to ensure the distance optical center is correctly positioned.

Question 2

What is the refractive index of standard CR-39 plastic lens material?

Accepted Answer

1.499

Answer

CR-39 (allyl diglycol carbonate) has a refractive index of approximately 1.499.

Question 3

Slab-off prism is used to correct vertical imbalance caused by:

Accepted Answer

Anisometropia when reading through off-center lenses

Answer

Slab-off (bicentric grinding) compensates for differential vertical prism induced by anisometropic lenses when the eyes depress for near tasks.

Question 4

A lens with a power of +4.00 D has a focal length of:

Accepted Answer

25 cm

Answer

Focal length (meters) = 1 / power (D), so 1/4.00 = 0.25 m = 25 cm.

Question 5

The phenomenon where a lens splits white light into its component colors is called:

Accepted Answer

Chromatic dispersion

Answer

Chromatic dispersion occurs because different wavelengths of light are refracted by different amounts, separating white light into colors.

NOCE - National Opticianry Competency Examination Practice Test