ABO NOCE Basic Opticianry Spectacle Lens Aberrations 3 — Questions and Answers
Question 1: Lateral chromatic aberration in spectacle lenses causes which visual symptom for the wearer?
- Central blur
- Color fringing at the edges of objects viewed peripherally (Correct answer)
- Monocular diplopia
- Reduced contrast sensitivity
Correct answer: Color fringing at the edges of objects viewed peripherally
Lateral chromatic aberration disperses colors at different lateral positions off-axis, causing colored fringes around objects viewed through the lens periphery.
Question 2: The Abbe value (V-number) of a lens material directly affects which type of aberration?
- Spherical aberration
- Distortion
- Chromatic aberration (Correct answer)
- Coma
Correct answer: Chromatic aberration
The Abbe value measures a material's dispersion; lower Abbe values indicate greater chromatic aberration in the finished lens.
Question 3: A patient complains of colored halos around lights when looking through the edge of their new high-index lenses. The most likely cause is:
- Anti-reflective coating failure
- Low Abbe value of the high-index material (Correct answer)
- Incorrect pupillary distance
- Base curve selection error
Correct answer: Low Abbe value of the high-index material
High-index materials typically have lower Abbe values, producing more chromatic aberration and colored fringes, especially in the lens periphery.
Question 4: Which of the following lens materials has the HIGHEST Abbe value (least chromatic aberration)?
- Polycarbonate (Abbe ~30)
- CR-39 plastic (Abbe ~58) (Correct answer)
- 1.74 high-index (Abbe ~33)
- Trivex (Abbe ~45)
Correct answer: CR-39 plastic (Abbe ~58)
CR-39 plastic has an Abbe value of approximately 58, giving it the least chromatic aberration among common spectacle lens materials.
Question 5: When comparing transverse (lateral) and longitudinal chromatic aberration, which statement is correct?
- Longitudinal CA causes color fringing; transverse CA causes axial blur
- Transverse CA causes color fringing; longitudinal CA causes axial blur (Correct answer)
- Both types produce identical visual symptoms
- Only longitudinal CA is clinically relevant in spectacle lenses
Correct answer: Transverse CA causes color fringing; longitudinal CA causes axial blur
Transverse (lateral) chromatic aberration displaces colors sideways causing fringing, while longitudinal CA separates colors along the optical axis causing axial blur.
Question 6: A patient with a -8.00 D prescription is most likely to notice chromatic aberration when:
- Looking through the optical center
- Reading fine print
- Looking through the peripheral area of the lens (Correct answer)
- Outdoors in bright sunlight
Correct answer: Looking through the peripheral area of the lens
Chromatic aberration increases with lens power and angle of viewing, making it most noticeable when viewing through peripheral lens zones in high prescriptions.
Question 7: Achromatic doublet lenses reduce chromatic aberration by:
- Using a single high-index element
- Combining two lens elements with different Abbe values and powers (Correct answer)
- Applying a special anti-reflective coating
- Increasing the lens center thickness
Correct answer: Combining two lens elements with different Abbe values and powers
An achromatic doublet pairs a crown glass element with a flint glass element of different Abbe values so their chromatic dispersions cancel each other.
ABO NOCE Basic Opticianry Spectacle Lens Aberrations 3
Lateral chromatic aberration in spectacle lenses causes which visual symptom for the wearer?