ABO NOCE Basic Opticianry Ophthalmic Optics and Principles Questions and Answers 5 — Questions and Answers
Question 1: What is the dioptric power of a plano-convex lens with a front surface radius of curvature of 100 mm in air (n=1.00, n'=1.50)?
- +5.00 D (Correct answer)
- +10.00 D
- +3.33 D
- +15.00 D
Correct answer: +5.00 D
Surface power = (n' − n) / r = (1.50 − 1.00) / 0.10 m = 0.50 / 0.10 = +5.00 D.
Question 2: Which term describes the ability of a lens material to polarize light at a specific angle, known as Brewster's angle?
- Anti-reflection
- Birefringence
- Polarization by reflection (Correct answer)
- Total internal reflection
Correct answer: Polarization by reflection
At Brewster's angle, reflected light becomes completely polarized parallel to the surface, which is the basis for polarized ophthalmic lenses reducing glare.
Question 3: When transposing −1.50 +2.00 × 090 into minus cylinder form, the result is:
- +0.50 −2.00 × 180 (Correct answer)
- +0.50 −2.00 × 090
- −1.50 −2.00 × 180
- +2.00 −1.50 × 090
Correct answer: +0.50 −2.00 × 180
Add sphere + cylinder = −1.50 + 2.00 = +0.50; reverse cylinder sign = −2.00; rotate axis 90° → 180°: result is +0.50 −2.00 × 180.
Question 4: A prism of 5Δ is prescribed base-up OD. In which direction does the image appear displaced to that eye?
- Upward (Correct answer)
- Downward
- Nasally
- Temporally
Correct answer: Upward
A base-up prism refracts light downward through the prism, making the image appear displaced upward (toward the apex).
Question 5: What is the minimum vertex distance that must be accounted for when converting a spectacle prescription to contact lens power, according to standard practice?
- Any prescription over ±0.50 D
- Any prescription over ±2.00 D
- Any prescription over ±4.00 D (Correct answer)
- All prescriptions regardless of power
Correct answer: Any prescription over ±4.00 D
By standard ophthalmic convention, vertex distance compensation is required when spectacle powers exceed ±4.00 D.
Question 6: A bifocal add creates a prismatic effect at the reading level. For a +2.50 add with the reading zone 8 mm below the optical center, what is the prismatic effect using Prentice's Rule?
- 2.0Δ base-down
- 2.0Δ base-up (Correct answer)
- 20Δ base-up
- 0.2Δ base-down
Correct answer: 2.0Δ base-up
Δ = D × c = 2.50 × 0.8 cm = 2.0Δ; a plus lens below its optical center produces base-up prism.
Question 7: Which optical effect occurs when white light passes through a prism and is separated into its component wavelengths?
- Diffraction
- Polarization
- Dispersion (Correct answer)
- Interference
Correct answer: Dispersion
Dispersion is the separation of white light into its spectrum because different wavelengths are refracted by different amounts through the prism.
ABO NOCE Basic Opticianry Ophthalmic Optics and Principles Questions and Answers 5
What is the dioptric power of a plano-convex lens with a front surface radius of curvature of 100 mm in air (n=1.00, n'=1.50)?