CPOA Ophthalmic Optics 3 — Questions and Answers
Question 1: What is the purpose of an anti-reflective (AR) coating on spectacle lenses?
- To add tint to the lens
- To reduce surface reflections and improve light transmission (Correct answer)
- To harden the lens surface
- To block ultraviolet radiation
Correct answer: To reduce surface reflections and improve light transmission
AR coatings reduce surface reflections through destructive interference, increasing the amount of light transmitted through the lens and reducing glare.
Question 2: Which lens design divides the lens into two zones — distance on top and near on the bottom — with a visible dividing line?
- Progressive addition lens
- Bifocal lens (Correct answer)
- Trifocal lens
- Occupational lens
Correct answer: Bifocal lens
A bifocal lens has a visible flat-top or round segment for near vision at the bottom and the distance prescription in the main lens above.
Question 3: What does base curve refer to in ophthalmic lens fabrication?
- The curve on the front surface of the lens (Correct answer)
- The optical center of the lens
- The edge thickness measurement
- The lens diameter specification
Correct answer: The curve on the front surface of the lens
The base curve is the curvature of the front (convex) surface of a lens, which influences the overall form and optical performance of the finished lens.
Question 4: Polycarbonate lenses are preferred for children and safety eyewear primarily because of their:
- Superior optical clarity
- Lightweight and high impact resistance (Correct answer)
- Lower cost than glass
- Better UV absorption than CR-39
Correct answer: Lightweight and high impact resistance
Polycarbonate is highly impact-resistant and lightweight, making it the preferred material for safety eyewear and children's glasses.
Question 5: A prism prescribed as '2Δ base up OD' would displace the image in which direction for the right eye?
- Downward (Correct answer)
- Upward
- Toward the nose
- Away from the nose
Correct answer: Downward
Base-up prism displaces the image downward, which is used to correct hyperphoria (eye deviating upward).
Question 6: What is chromatic aberration in ophthalmic lenses?
- Color distortion from lens tinting
- The separation of white light into its component colors by the lens (Correct answer)
- Scratches that scatter colored light
- UV light causing lens yellowing
Correct answer: The separation of white light into its component colors by the lens
Chromatic aberration occurs because a lens refracts different wavelengths of light by slightly different amounts, causing colored fringes at the edges of objects.
Question 7: What is the primary optical advantage of a lenticular lens design?
- Improved cosmetic appearance for very high prescriptions (Correct answer)
- Better near vision correction
- Enhanced peripheral vision
- Reduced photophobia
Correct answer: Improved cosmetic appearance for very high prescriptions
Lenticular lenses place the optical correction in a central 'bowl' surrounded by a carrier lens, reducing edge thickness and weight for very high prescriptions.
CPOA Ophthalmic Optics 3
What is the purpose of an anti-reflective (AR) coating on spectacle lenses?