ABO ABO Industry Standards 5 — Questions and Answers
Question 1: Prentice's rule states that induced prism equals:
- Power (D) × decentration (cm) (Correct answer)
- Power (D) / decentration (mm)
- Power (D) × decentration (mm)
- Power (D) + decentration (cm)
Correct answer: Power (D) × decentration (cm)
Prentice's rule: Prism (Δ) = Power (diopters) × decentration (centimeters), used to calculate induced prism from lens decentration.
Question 2: What is the base curve of an ophthalmic lens?
- The curve on the front surface of the lens
- The flattest curve on the lens surface
- The curve specifically designated as the reference or 'base' from which other curves are measured (Correct answer)
- The curve ground on the back surface of the lens
Correct answer: The curve specifically designated as the reference or 'base' from which other curves are measured
The base curve is the reference surface curve (usually the front curve) from which the lens prescription is built and other curves are calculated.
Question 3: Under ANSI Z80.3, sunlens luminous transmittance categories range from Category 0 to Category 4. What does Category 4 indicate?
- Clear lenses with no tint, 80-100% transmittance
- Light tints suitable for indoor use, 43-80% transmittance
- Medium tints for general use, 18-43% transmittance
- Very dark lenses (3-8% transmittance) not suitable for driving (Correct answer)
Correct answer: Very dark lenses (3-8% transmittance) not suitable for driving
Category 4 sunlenses have very dark tints with only 3-8% luminous transmittance and are not recommended for use while driving.
Question 4: In frame standards, the 'boxing system' is used to:
- Measure the impact resistance of the frame
- Provide a standardized method for measuring lens and frame dimensions (Correct answer)
- Classify frames by material type
- Determine the recommended pupillary distance for the frame
Correct answer: Provide a standardized method for measuring lens and frame dimensions
The boxing system is a standardized method using a rectangle (box) around the lens aperture to measure frame and lens dimensions such as A, B, DBL, and ED.
Question 5: What is the 'effective diameter' (ED) of a lens in the boxing system?
- The diameter of the lens at its widest horizontal point
- The diameter of the lens at its widest vertical point
- The diameter of the smallest circle that will encompass the entire lens shape (Correct answer)
- The distance between the two geometric centers of both lenses
Correct answer: The diameter of the smallest circle that will encompass the entire lens shape
The effective diameter (ED) is the diameter of the smallest circle centered on the boxing center that completely encloses the lens shape.
Question 6: According to ANSI Z80.1, what is the cylinder power tolerance for lenses with cylinder powers greater than 2.00D?
- ±0.13D
- ±0.15D
- ±0.16D
- ±5% of the specified cylinder (Correct answer)
Correct answer: ±5% of the specified cylinder
For cylinder powers exceeding 2.00D, ANSI Z80.1 allows a tolerance of ±5% of the specified cylinder power.
Question 7: Which of the following correctly describes 'wrap angle' (face-form tilt) in frame fitting?
- The vertical tilt of the lens from front to back
- The angle at which the frame front curves horizontally to follow the face (Correct answer)
- The angle of the temple relative to the frame front
- The tilt of the nose pads relative to the bridge
Correct answer: The angle at which the frame front curves horizontally to follow the face
Wrap angle (face-form tilt) is the horizontal curvature of the frame front that follows the contour of the patient's face.
ABO ABO Industry Standards 5
Prentice's rule states that induced prism equals: