ABO NOCE Basic Opticianry Ophthalmic Optics and Principles 3 — Questions and Answers
Question 1: Which aberration causes off-axis image points to appear as lines or streaks rather than sharp points?
- Spherical aberration
- Chromatic aberration
- Coma
- Astigmatism of oblique incidence (Correct answer)
Correct answer: Astigmatism of oblique incidence
Astigmatism of oblique incidence occurs when light strikes a lens at an angle, producing two focal lines (sagittal and tangential) instead of a point focus.
Question 2: What does the Abbe number (V-number) of a lens material indicate?
- The material's density
- The degree of chromatic dispersion (Correct answer)
- The scratch resistance
- The UV absorption
Correct answer: The degree of chromatic dispersion
The Abbe number measures how much a material disperses light into its component colors; a higher Abbe number means less chromatic aberration.
Question 3: A patient's prescription reads -2.00 -1.00 × 090. What is the power in the 180° meridian?
- -2.00 D
- -3.00 D (Correct answer)
- -1.00 D
- 0.00 D
Correct answer: -3.00 D
The 180° meridian is 90° away from the cylinder axis (090), so the full cylinder power is added: -2.00 + (-1.00) = -3.00 D.
Question 4: What is the focal length of a +4.00 D lens?
- 4 cm
- 25 cm (Correct answer)
- 40 cm
- 4 m
Correct answer: 25 cm
Focal length (m) = 1/Power(D) = 1/4 = 0.25 m = 25 cm.
Question 5: When transposing -3.00 +1.50 × 045, what is the correct transposition?
- -1.50 -1.50 × 135 (Correct answer)
- -1.50 +1.50 × 045
- -1.50 -1.50 × 045
- +1.50 -3.00 × 135
Correct answer: -1.50 -1.50 × 135
Transposition: new sphere = algebraic sum (-3.00+1.50=-1.50), new cylinder = sign-changed (-1.50), new axis = 90° rotated (045+90=135).
Question 6: What is the primary purpose of antireflection (AR) coatings on ophthalmic lenses?
- To increase lens thickness
- To reduce surface reflections and improve light transmission (Correct answer)
- To add UV protection
- To harden the lens surface
Correct answer: To reduce surface reflections and improve light transmission
AR coatings use thin-film interference to cancel reflected light, increasing light transmission and reducing glare for the wearer.
Question 7: Which of the following best describes a Fresnel prism?
- A thick glass prism for strong prescriptions
- A thin flexible sheet with prismatic grooves (Correct answer)
- A prism ground into the lens edge
- A prism used only in sunglasses
Correct answer: A thin flexible sheet with prismatic grooves
Fresnel prisms are thin, lightweight press-on sheets with concentric prismatic ridges that provide prismatic effect without significant weight or thickness.
ABO NOCE Basic Opticianry Ophthalmic Optics and Principles 3
Which aberration causes off-axis image points to appear as lines or streaks rather than sharp points?