ABO NOCE Basic Opticianry Spectacle Lens Aberrations 2 — Questions and Answers
Question 1: Which aberration causes straight lines to appear curved when viewed through the periphery of a lens?
- Spherical aberration
- Distortion (Correct answer)
- Coma
- Oblique astigmatism
Correct answer: Distortion
Distortion causes straight lines to appear curved or bowed, with pincushion distortion in plus lenses and barrel distortion in minus lenses.
Question 2: Pincushion distortion is most commonly associated with which type of lens?
- High minus lenses
- High plus lenses (Correct answer)
- Piano lenses
- Photochromic lenses
Correct answer: High plus lenses
High plus (convex) lenses produce pincushion distortion, where the edges of images appear to bow inward.
Question 3: What is the primary optical aberration corrected by aspheric lens designs?
- Chromatic aberration
- Distortion
- Spherical aberration (Correct answer)
- Coma
Correct answer: Spherical aberration
Aspheric lens designs flatten the lens surface progressively from center to edge to reduce spherical aberration.
Question 4: Oblique astigmatism occurs when light rays pass through a lens at an angle. At what lens zone is this aberration most problematic?
- Optical center
- Near zone
- Peripheral zone (Correct answer)
- Progressive corridor
Correct answer: Peripheral zone
Oblique astigmatism is a peripheral aberration that worsens as the angle of incidence increases away from the optical center.
Question 5: Which Seidel aberration creates a comet-shaped blur and is caused by off-axis light passing through different lens zones?
- Distortion
- Field curvature
- Coma (Correct answer)
- Chromatic aberration
Correct answer: Coma
Coma produces a comet-shaped flare pattern because off-axis rays through outer lens zones focus at different lateral positions than paraxial rays.
Question 6: Field curvature aberration means the image formed by a lens lies on a curved surface rather than a flat plane. How does this affect the wearer?
- Central vision is blurred while peripheral is clear
- The entire visual field appears equally sharp
- Peripheral objects cannot be brought to sharp focus simultaneously with central objects (Correct answer)
- Colors appear separated at the edges of vision
Correct answer: Peripheral objects cannot be brought to sharp focus simultaneously with central objects
Field curvature causes the best focus to lie on a curved surface, so peripheral and central objects cannot be simultaneously in sharp focus.
Question 7: Which lens design feature helps minimize the combined effect of oblique astigmatism and field curvature in spectacle lenses?
- Tinted coating
- Best-form (corrected curve) design (Correct answer)
- Anti-reflective coating
- Polycarbonate material
Correct answer: Best-form (corrected curve) design
Best-form lens design selects specific base curves that minimize oblique astigmatism and field curvature for a given prescription.
ABO NOCE Basic Opticianry Spectacle Lens Aberrations 2
Which aberration causes straight lines to appear curved when viewed through the periphery of a lens?