ABO NOCE Basic Opticianry Ophthalmic Lenses and Materials Questions and Answers 3 — Questions and Answers
Question 1: What is the purpose of an 'aspheric' lens design in ophthalmic optics?
- To increase lens thickness for durability
- To reduce peripheral aberrations and allow a flatter, thinner lens (Correct answer)
- To add UV protection without coatings
- To eliminate the need for anti-reflective treatment
Correct answer: To reduce peripheral aberrations and allow a flatter, thinner lens
Aspheric surfaces vary in curvature from center to periphery, reducing oblique aberrations and enabling flatter, more cosmetically appealing lenses.
Question 2: Which property of lens materials is measured by the Abbe number (V-value)?
- Impact resistance
- UV transmission
- Chromatic dispersion (color fringing) (Correct answer)
- Specific gravity
Correct answer: Chromatic dispersion (color fringing)
The Abbe number quantifies chromatic aberration—how much a material splits white light into its component colors.
Question 3: When edging a polycarbonate lens, which wheel type is recommended?
- Diamond-coated wheel at high speed
- Silicon carbide wheel at low speed
- Diamond-coated wheel at reduced speed with coolant (Correct answer)
- Standard glass-cutting wheel
Correct answer: Diamond-coated wheel at reduced speed with coolant
Polycarbonate requires diamond-coated wheels run at slower speeds with coolant to prevent crazing and delamination.
Question 4: What is 'prism thinning' in lens fabrication?
- Adding base-down prism to all lenses
- Splitting prescribed prism between two lenses to minimize thickness (Correct answer)
- Removing prism from a finished lens by polishing
- Calculating the thinnest possible lens edge
Correct answer: Splitting prescribed prism between two lenses to minimize thickness
Prism thinning (or prism splitting) distributes prescribed prism equally between both eyes to minimize the thickness of each lens.
Question 5: A lens is described as 'lenticular.' What does this indicate?
- It has two different refractive indices
- Only a central portion (aperture) carries the prescription; the carrier is plano or reduced power (Correct answer)
- It is designed for contact lens use
- It contains photochromic dye throughout
Correct answer: Only a central portion (aperture) carries the prescription; the carrier is plano or reduced power
Lenticular lenses have a central optical zone with the full prescription and a surrounding carrier of different (often zero) power to reduce weight and thickness.
Question 6: Which statement about photochromic lenses is correct?
- They darken in response to heat, not UV
- They darken faster in cold temperatures but lighten more slowly (Correct answer)
- They do not provide UV protection in the clear state
- They work normally behind automotive windshields
Correct answer: They darken faster in cold temperatures but lighten more slowly
Photochromic lenses activate faster in cold temperatures but fade back to clear more slowly because the chemical reaction is temperature-dependent.
Question 7: What is the relationship between lens power and focal length?
- Power (D) = focal length (m)
- Power (D) = 1 / focal length (m) (Correct answer)
- Power (D) = focal length (cm) × 10
- Power (D) = focal length (mm) / 100
Correct answer: Power (D) = 1 / focal length (m)
Lens power in diopters equals the reciprocal of the focal length in meters: P = 1/f.
ABO NOCE Basic Opticianry Ophthalmic Lenses and Materials Questions and Answers 3
What is the purpose of an 'aspheric' lens design in ophthalmic optics?