ABO NOCE Basic Opticianry Ophthalmic Optics and Principles 5 — Questions and Answers
Question 1: What type of lens corrects presbyopia by providing different optical zones for distance and near vision?
- Single vision lens
- Bifocal lens (Correct answer)
- Toric lens
- Plano lens
Correct answer: Bifocal lens
A bifocal lens has two distinct optical zones—one for distance and one for near—to compensate for the loss of accommodation in presbyopia.
Question 2: What is the 'add power' in a progressive lens prescription?
- The base curve of the lens
- The additional plus power for near vision over the distance Rx (Correct answer)
- The prismatic power at the optical center
- The UV filter strength
Correct answer: The additional plus power for near vision over the distance Rx
Add power is the additional plus power required for near vision, added to the distance prescription to compensate for reduced accommodation.
Question 3: Which of the following is true about total internal reflection?
- It occurs when light moves from a less dense to a more dense medium
- It occurs when the angle of incidence exceeds the critical angle in a denser medium (Correct answer)
- It increases lens power
- It only occurs in mirrors
Correct answer: It occurs when the angle of incidence exceeds the critical angle in a denser medium
Total internal reflection occurs when light in a denser medium strikes the boundary at an angle greater than the critical angle, causing all light to reflect back.
Question 4: A prism base-down before the right eye would cause the image to appear displaced in which direction?
- Down
- Up (Correct answer)
- Left
- Right
Correct answer: Up
A prism displaces images toward the apex; base-down means the apex is up, so the image appears displaced upward.
Question 5: What does the term 'sag' (sagitta) refer to in ophthalmic lens design?
- The weight of the lens
- The depth of a curved surface measured from its chord (Correct answer)
- The axis of the cylinder
- The lens edge thickness
Correct answer: The depth of a curved surface measured from its chord
The sag (sagitta) is the perpendicular depth from the chord of a curved surface to the surface itself, important for calculating lens thickness.
Question 6: What is the primary optical difference between a flat-top 28 bifocal and an executive bifocal?
- Executive bifocals have a round near segment
- Executive bifocals have the near segment spanning the full width of the lens (Correct answer)
- Flat-top 28 has a wider near zone
- There is no optical difference
Correct answer: Executive bifocals have the near segment spanning the full width of the lens
The executive (Franklin) bifocal's near segment extends across the entire width of the lens, while the flat-top 28 has a smaller, defined near segment.
Question 7: What is 'chromatic aberration' in ophthalmic lenses?
- Lens discoloration from UV exposure
- The separation of white light into spectral colors due to dispersion (Correct answer)
- Distortion at high prescriptions
- Reflections from lens surfaces
Correct answer: The separation of white light into spectral colors due to dispersion
Chromatic aberration occurs because different wavelengths of light are refracted by different amounts, causing color fringing at lens edges.
ABO NOCE Basic Opticianry Ophthalmic Optics and Principles 5
What type of lens corrects presbyopia by providing different optical zones for distance and near vision?