NOCE Ophthalmic Optics and Lenses 2 — Questions and Answers
Question 1: A lens with a base curve of +6.00 D and a back surface power of -2.50 D has what front vertex power?
- +3.50 D (Correct answer)
- +8.50 D
- -3.50 D
- +3.00 D
Correct answer: +3.50 D
Front vertex power equals base curve plus back surface power: +6.00 + (-2.50) = +3.50 D.
Question 2: Which lens form produces the least amount of oblique astigmatism for a given prescription?
- Best form (corrected curve) lens (Correct answer)
- Flat lens
- Plano-convex lens
- Biconvex lens
Correct answer: Best form (corrected curve) lens
Best form lenses are designed with optimal base curves to minimize oblique astigmatism and peripheral distortions.
Question 3: A patient requires a prism of 4Δ base-in for the right eye. If split equally, how much prism is ground on each lens?
- 2Δ base-in on each lens (Correct answer)
- 4Δ base-in on each lens
- 2Δ base-out on each lens
- 1Δ base-in on each lens
Correct answer: 2Δ base-in on each lens
When prism is split equally, half the total prism (2Δ) is placed base-in on each lens.
Question 4: The critical angle in optics refers to the angle at which:
- Total internal reflection occurs (Correct answer)
- Refraction is maximized
- Light absorption is greatest
- Dispersion is eliminated
Correct answer: Total internal reflection occurs
The critical angle is the minimum angle of incidence at which total internal reflection occurs at the interface between a denser and less dense medium.
Question 5: What is the effect of increasing a lens's center thickness on its optical performance?
- Increases back vertex power (Correct answer)
- Decreases front vertex power
- Has no effect on power
- Increases the index of refraction
Correct answer: Increases back vertex power
Increasing center thickness increases the back vertex power of a plus lens due to the lens clock effect.
Question 6: A lens marked with a red dot indicates:
- The temporal side for progressive lenses (Correct answer)
- The optical center location
- A photochromic coating
- The prism reference point
Correct answer: The temporal side for progressive lenses
Red dots on progressive lenses mark the temporal side to help with proper orientation during dispensing.
Question 7: When measuring vertex distance, which surface of the lens is measured to the cornea?
- Back surface (ocular side) (Correct answer)
- Front surface (object side)
- Geometric center
- Optical center
Correct answer: Back surface (ocular side)
Vertex distance is measured from the back (ocular) surface of the lens to the front of the cornea.
NOCE Ophthalmic Optics and Lenses 2
A lens with a base curve of +6.00 D and a back surface power of -2.50 D has what front vertex power?