Spectacle Lens Aberrations Flashcards
7 cards from real ABO NOCE Basic Opticianry practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Spectacle Lens Aberrations flashcards as text
In the context of Seidel aberrations, which two aberrations are most clinically significant for spectacle lens wearers?
Answer: Oblique astigmatism and distortion
Oblique astigmatism and distortion are the two most visually disruptive Seidel aberrations in spectacle lenses, particularly at high prescriptions.
How does increasing the vertex distance (back vertex distance) of a spectacle lens affect peripheral aberrations?
Answer: Increases peripheral aberrations, especially oblique astigmatism
A larger vertex distance increases the angle at which peripheral rays strike the lens, worsening oblique astigmatism and other off-axis aberrations.
Which patient scenario would experience the MOST noticeable spherical aberration?
Answer: High hyperope (+6.00 D) with a large pupil in dim light
Spherical aberration increases with both lens power and pupil size, so a high plus prescription combined with a large pupil produces maximum spherical aberration.
A patient reports that rectangular doorframes appear to bow outward (barrel-shaped) when wearing new glasses. This is consistent with which aberration and prescription type?
Answer: Barrel distortion from a minus lens
Barrel distortion, where straight lines bow outward, is characteristic of minus (concave) lenses.
The Tscherning ellipse is a tool used in spectacle lens design to:
Answer: Identify base curves that minimize oblique astigmatism for given powers
The Tscherning ellipse plots lens power against base curve to identify the specific curves that minimize oblique astigmatism for each prescription power.
Free-form (digital surfacing) lens technology primarily benefits patients by:
Answer: Reducing peripheral aberrations through customized back surface optimization
Free-form technology uses computer-controlled surfacing to create a customized back surface that compensates for aberrations across the entire lens, improving peripheral clarity.
Which statement correctly describes the relationship between lens power and oblique astigmatism?
Answer: Higher power lenses produce more oblique astigmatism in the periphery
Oblique astigmatism increases with lens power because stronger lenses refract peripheral (oblique) rays more dramatically, creating greater astigmatic error.