NOCE Ophthalmic Optics and Formulas 2

Question 1

Using Prentice's rule, how much prism is induced when a patient looks 8mm below the optical center of a +3.00 D lens?

Accepted Answer

2.4 prism diopters

Answer

Prentice's rule: P = d × F = 0.8 cm × 3.00 = 2.4 prism diopters.

Question 2

What is the focal length of a +4.00 diopter lens?

Accepted Answer

25 cm

Answer

Focal length f = 1/D = 1/4.00 = 0.25 meters = 25 cm.

Question 3

Light diverging from a point source located 50 cm away has a vergence of:

Accepted Answer

-2.00 D

Answer

Diverging light has negative vergence; V = -1/0.50 m = -2.00 D.

Question 4

A lens has a front surface power of +8.00 D and a back surface power of -4.00 D. What is its approximate total power?

Accepted Answer

+4.00 D

Answer

Approximate total power = +8.00 + (−4.00) = +4.00 D (thin lens approximation).

Question 5

A prism with its base at 270° will displace the image in which direction?

Accepted Answer

Upward

Answer

The image is displaced toward the prism apex; base at 270° (down) means the apex is up, so the image shifts upward.

NOCE - National Opticianry Competency Examination Practice Test