ABO Optics & Lens Design 2 — Questions and Answers
Question 1: Progressive addition lenses (PALs) differ from bifocals primarily because they:
- Provide only distance correction
- Have a visible dividing line
- Offer a gradual power change from distance to near (Correct answer)
- Are thicker at the center
Correct answer: Offer a gradual power change from distance to near
PALs provide a continuous, gradual power progression eliminating the visible segment line of bifocals.
Question 2: Add power in a bifocal lens is defined as:
- Distance power minus intermediate power
- Near power minus distance power (Correct answer)
- The difference between OD and OS
- The horizontal minus vertical power
Correct answer: Near power minus distance power
Add power equals the near prescription power minus the distance prescription power and is always a positive value.
Question 3: Lenticular lens design is most commonly used when:
- High minus powers are needed
- Very high plus powers are needed (Correct answer)
- Prism correction is needed
- Anti-reflective coating is applied
Correct answer: Very high plus powers are needed
Lenticular design places full correction only in a central optical zone, reducing weight and thickness for very high plus prescriptions.
Question 4: Aspheric lens surfaces are used primarily to:
- Increase lens thickness for strength
- Add UV protection
- Reduce peripheral aberrations and allow a flatter lens profile (Correct answer)
- Increase chromatic aberration
Correct answer: Reduce peripheral aberrations and allow a flatter lens profile
Aspheric surfaces vary in curvature across the lens to minimize spherical and peripheral aberrations while enabling a thinner, flatter design.
Question 5: In a toric lens, the two principal meridians are oriented:
- Parallel to each other
- At a 45° oblique angle
- Perpendicular to each other (Correct answer)
- Identical in power
Correct answer: Perpendicular to each other
A toric lens has two principal meridians at 90° to each other, each with a different curvature and power, correcting astigmatism.
Question 6: Polycarbonate lenses are the preferred material for safety eyewear primarily because of their:
- High Abbe value reducing chromatic aberration
- High refractive index
- Superior impact resistance (Correct answer)
- Lower cost compared to glass
Correct answer: Superior impact resistance
Polycarbonate's exceptional impact resistance makes it the material of choice for safety, sports, and children's eyewear.
ABO Optics & Lens Design 2
Progressive addition lenses (PALs) differ from bifocals primarily because they: