CPOA Ophthalmic Optics 4 — Questions and Answers
Question 1: What does the addition (ADD) power in a bifocal or progressive prescription represent?
- The total reading power of the lens
- The extra plus power added to distance Rx for near vision (Correct answer)
- The cylinder power for astigmatism correction
- The prism amount for binocular correction
Correct answer: The extra plus power added to distance Rx for near vision
The ADD power is the additional plus power added to the distance prescription to bring near objects into focus for presbyopic patients.
Question 2: Which lens material has the highest Abbe value among commonly used ophthalmic lens materials?
- Polycarbonate
- Trivex
- CR-39 plastic (Correct answer)
- 1.74 high-index plastic
Correct answer: CR-39 plastic
CR-39 plastic has an Abbe value of approximately 58, which is the highest among common ophthalmic materials, meaning it produces the least chromatic aberration.
Question 3: A patient complains of 'swim' or image movement when they move their head while wearing new progressive lenses. This is most likely caused by:
- Incorrect base curve selection
- Peripheral distortion inherent to progressive lens design (Correct answer)
- Excessive anti-reflective coating
- Lens material with too high an index
Correct answer: Peripheral distortion inherent to progressive lens design
Progressive addition lenses have areas of peripheral distortion and aberration that can cause a 'swimming' sensation, especially during adaptation.
Question 4: What is the optical significance of the geometric center versus the optical center of a lens?
- They are always the same point
- The optical center is where prism power is zero; the geometric center is the physical middle of the lens (Correct answer)
- The geometric center is where prescription power is measured
- They differ only in aspheric lens designs
Correct answer: The optical center is where prism power is zero; the geometric center is the physical middle of the lens
The optical center is the point through which light passes without prismatic deviation, while the geometric center is simply the physical middle of the lens blank.
Question 5: When dispensing high minus lenses, which edge treatment is most important for cosmetic and comfort reasons?
- Polish the front surface
- Roll and polish or bevel the thick edge (Correct answer)
- Apply anti-reflective coating only
- Use a flat-top bifocal segment
Correct answer: Roll and polish or bevel the thick edge
High minus lenses are thickest at the edges, so rolling and polishing (or proper beveling) improves cosmetics and reduces the 'ring' appearance of thick edges.
Question 6: What does 'aspheric' mean in reference to ophthalmic lens design?
- The lens has no sphere power
- The lens surface curves gradually change to reduce peripheral aberrations (Correct answer)
- The lens is designed for astigmatic corrections only
- The lens surface is perfectly spherical
Correct answer: The lens surface curves gradually change to reduce peripheral aberrations
Aspheric lenses have surfaces that gradually flatten toward the periphery, reducing spherical aberration and allowing for thinner, flatter lens profiles.
Question 7: Photochromic lenses darken in response to which type of radiation?
- Infrared radiation
- Ultraviolet radiation (Correct answer)
- Blue light
- Visible light
Correct answer: Ultraviolet radiation
Photochromic molecules in these lenses are activated by ultraviolet radiation, causing the lens to darken; they lighten indoors where UV is absent.
CPOA Ophthalmic Optics 4
What does the addition (ADD) power in a bifocal or progressive prescription represent?