NOCE Ophthalmic Optics and Formulas 2 — Questions and Answers
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?
- 1.8 prism diopters
- 2.4 prism diopters (Correct answer)
- 3.2 prism diopters
- 0.8 prism diopters
Correct answer: 2.4 prism diopters
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?
- 40 cm
- 25 cm (Correct answer)
- 50 cm
- 20 cm
Correct answer: 25 cm
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:
- +2.00 D
- -2.00 D (Correct answer)
- +0.50 D
- -0.50 D
Correct answer: -2.00 D
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?
- +4.00 D (Correct answer)
- +12.00 D
- -4.00 D
- +2.00 D
Correct answer: +4.00 D
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?
- Upward (Correct answer)
- Downward
- Nasally
- Temporally
Correct answer: Upward
The image is displaced toward the prism apex; base at 270° (down) means the apex is up, so the image shifts upward.
Question 6: Using the lensmaker's equation with n=1.50, r₁=+200 mm, and r₂=+400 mm, what is the approximate lens power?
- +0.63 D
- +1.25 D (Correct answer)
- +2.50 D
- +3.75 D
Correct answer: +1.25 D
F = (n−1)(1/r₁ − 1/r₂) = 0.50 × (5.00 − 2.50) = +1.25 D.
Question 7: If a patient needs 2 prism diopters base-in for each eye, what is the total convergence demand reduced?
- 1 prism diopter
- 2 prism diopters
- 4 prism diopters (Correct answer)
- 8 prism diopters
Correct answer: 4 prism diopters
Base-in prism in both eyes reduces convergence demand; 2Δ BI OD + 2Δ BI OS = 4Δ total.
NOCE Ophthalmic Optics and Formulas 2
Using Prentice's rule, how much prism is induced when a patient looks 8mm below the optical center of a +3.00 D lens?