Spectacle Lens Aberrations Flashcards

Which aberration causes straight lines to appear curved when viewed through the periphery of a lens?

Answer: Distortion

Distortion causes straight lines to appear curved or bowed, with pincushion distortion in plus lenses and barrel distortion in minus lenses.

Pincushion distortion is most commonly associated with which type of lens?

Answer: High plus lenses

High plus (convex) lenses produce pincushion distortion, where the edges of images appear to bow inward.

What is the primary optical aberration corrected by aspheric lens designs?

Answer: Spherical aberration

Aspheric lens designs flatten the lens surface progressively from center to edge to reduce spherical aberration.

Oblique astigmatism occurs when light rays pass through a lens at an angle. At what lens zone is this aberration most problematic?

Answer: Peripheral zone

Oblique astigmatism is a peripheral aberration that worsens as the angle of incidence increases away from the optical center.

Which Seidel aberration creates a comet-shaped blur and is caused by off-axis light passing through different lens zones?

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.

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?

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.

Which lens design feature helps minimize the combined effect of oblique astigmatism and field curvature in spectacle lenses?

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.