ABO Ophthalmic Dispensing — Questions and Answers
Question 1: What is the minimum thickness requirement for safety lenses meeting ANSI Z87.1 standards?
- 2.0 mm for glass lenses (Correct answer)
- 1.0 mm for all lenses
- 3.0 mm for polycarbonate
- 0.5 mm for trivex
Correct answer: 2.0 mm for glass lenses
ANSI Z87.1 safety standards require dress safety glass lenses to have a minimum thickness of 2.0 mm. Polycarbonate and trivex have different requirements due to their impact resistance.
Question 2: Which lens material has the highest index of refraction among common ophthalmic materials?
- High-index 1.74 plastic (Correct answer)
- Crown glass (1.523)
- Polycarbonate (1.586)
- CR-39 (1.498)
Correct answer: High-index 1.74 plastic
High-index 1.74 plastic has the highest index of refraction commonly available, allowing the thinnest possible lens for high prescriptions.
Question 3: What measurement determines the vertical position of a progressive lens on the patient's face?
- Fitting height (Correct answer)
- Pupillary distance
- Pantoscopic tilt
- Frame wrap angle
Correct answer: Fitting height
The fitting height measures from the bottom of the lens to the center of the pupil, crucial for proper placement of the progressive corridor.
Question 4: Which frame measurement represents the longest horizontal dimension of the lens opening?
- Eye size (A dimension) (Correct answer)
- Bridge size (DBL)
- Temple length
- B dimension
Correct answer: Eye size (A dimension)
The eye size or A dimension represents the longest horizontal measurement of the lens shape in a frame, measured in millimeters.
Question 5: What is the primary advantage of polycarbonate lenses over CR-39?
- Superior impact resistance (Correct answer)
- Better optical clarity
- Higher Abbe value
- Easier to tint
Correct answer: Superior impact resistance
Polycarbonate is significantly more impact-resistant than CR-39, making it the preferred material for safety eyewear and children's glasses.
Question 6: When is it appropriate to use a slab-off prism?
- To correct vertical imbalance in anisometropic patients wearing multifocals (Correct answer)
- To correct horizontal phoria
- To reduce lens thickness in high minus prescriptions
- To improve cosmetic appearance of thick lenses
Correct answer: To correct vertical imbalance in anisometropic patients wearing multifocals
Slab-off (bicentric grinding) is used to neutralize the differential vertical prismatic effect that occurs when anisometropic patients look through the near segment of multifocal lenses.
ABO Ophthalmic Dispensing
What is the minimum thickness requirement for safety lenses meeting ANSI Z87.1 standards?