CPOT CPOT Optical Dispensing & Lens Technology 1 — Questions and Answers
Question 1: Which lens material has the highest Abbe value, indicating the least chromatic aberration?
- Polycarbonate
- Trivex
- CR-39 plastic (Correct answer)
- High-index 1.74
Correct answer: CR-39 plastic
CR-39 plastic has an Abbe value of approximately 58, the highest among common ophthalmic lens materials, resulting in the least color fringing.
Question 2: A lens prescription written as -2.00 -1.50 × 090 indicates:
- Hyperopia with no astigmatism
- Myopia with astigmatism, axis at 90 degrees (Correct answer)
- Hyperopia with astigmatism, axis at 180 degrees
- Emmetropia with astigmatism
Correct answer: Myopia with astigmatism, axis at 90 degrees
A minus sphere power indicates myopia, the minus cylinder corrects astigmatism, and the axis of 090° specifies the orientation of the cylinder.
Question 3: Pupillary distance (PD) is measured to ensure that the optical centers of the lenses align with the:
- Outer canthi of each eye
- Center of each pupil (Correct answer)
- Inner canthi of each eye
- Center of each iris
Correct answer: Center of each pupil
PD measurement centers the optical zones of the lenses over each pupil to minimize induced prism and provide optimal visual comfort.
Question 4: Antireflective (AR) coating on ophthalmic lenses primarily works by:
- Hardening the lens surface
- Absorbing UV radiation
- Using thin-film interference to cancel reflected light (Correct answer)
- Tinting the lens to reduce glare
Correct answer: Using thin-film interference to cancel reflected light
AR coatings use multiple thin layers that create destructive interference, canceling reflected light and increasing light transmission to the eye.
Question 5: Which type of lens is recommended for patients who need correction for distance, intermediate, and near vision in a single lens without visible lines?
- Bifocal
- Trifocal
- Progressive addition lens (PAL) (Correct answer)
- Single vision lens
Correct answer: Progressive addition lens (PAL)
Progressive addition lenses provide a smooth, gradual power change from distance at the top to near at the bottom, with no visible segment lines.
Question 6: The base curve of an ophthalmic lens is defined as:
- The total power of the lens
- The curvature of the back surface
- The reference curve from which other lens curves are calculated (Correct answer)
- The thickness at the lens edge
Correct answer: The reference curve from which other lens curves are calculated
The base curve is the standard reference surface of a lens blank from which the other curves are derived to achieve the desired prescription power.
CPOT CPOT Optical Dispensing & Lens Technology 1
Which lens material has the highest Abbe value, indicating the least chromatic aberration?