ABO NOCE Basic Opticianry Dispensing Instrumentation 5 — Questions and Answers
Question 1: If a lensometer reading shows the sphere drum at +2.00 and the cylinder drum at +0.75 at axis 90, the lens power in minus-cylinder form is:
- +2.75 -0.75 × 180 (Correct answer)
- +2.00 +0.75 × 90
- +2.75 -0.75 × 90
- +2.00 -0.75 × 90
Correct answer: +2.75 -0.75 × 180
Converting plus-cylinder lensometer readings to minus-cylinder: add sphere+cylinder to get the new sphere (+2.75), change cylinder sign (-0.75), and rotate axis 90° (180).
Question 2: The three ink dots made by a lensometer dotting device on a finished lens represent:
- The bifocal segment location, OC, and prism reference point
- The optical center (center dot) and reference points for horizontal axis alignment (outer dots) (Correct answer)
- The near, intermediate, and distance zones of a progressive lens
- The three prism diopter reference points for slab-off verification
Correct answer: The optical center (center dot) and reference points for horizontal axis alignment (outer dots)
The center dot marks the optical center and the two outer dots establish the horizontal meridian used to properly align the lens during edging.
Question 3: An ultrasonic cleaner in an optical dispensary is used to:
- Resurface scratched lenses
- Clean frames and lenses using high-frequency sound waves in a cleaning solution (Correct answer)
- Measure lens curvature
- Apply anti-reflective coatings
Correct answer: Clean frames and lenses using high-frequency sound waves in a cleaning solution
Ultrasonic cleaners use high-frequency vibrations in a liquid solution to remove skin oils, debris, and contaminants from frames and lenses without abrasion.
Question 4: When using a frame warmer on a metal frame with plastic temples, the optician should:
- Heat the metal bridge aggressively with direct flame
- Use only the hot-air blower on the plastic portions and use pliers for metal adjustments (Correct answer)
- Soak the entire frame in boiling water for 5 minutes
- Apply high heat to all parts simultaneously
Correct answer: Use only the hot-air blower on the plastic portions and use pliers for metal adjustments
Plastic temple tips and components can be softened with a hot-air blower, while metal frame parts are adjusted with appropriate pliers rather than direct heat.
Question 5: A temple-bending iron (or angling pliers) is used to create or adjust which frame feature?
- The pantoscopic tilt of the lens plane
- The drop (angle) at the bend where the temple transitions behind the ear (Correct answer)
- The optical center height of the lens
- The face-form curvature of the front frame
Correct answer: The drop (angle) at the bend where the temple transitions behind the ear
A temple-bending iron or angling pliers adjusts the earpiece bend angle and drop to ensure proper fit behind and over the patient's ear.
Question 6: The primary reason an optician verifies the finished glasses on the lensometer before dispensing to the patient is:
- To reset the optical centers after the lenses have been edged
- To confirm the lenses match the prescribed power, axis, add, and prism within ANSI tolerances (Correct answer)
- To apply a UV coating to the lenses
- To measure the patient's current visual acuity
Correct answer: To confirm the lenses match the prescribed power, axis, add, and prism within ANSI tolerances
Final lensometer verification ensures the dispensed lenses meet the prescription and fall within ANSI Z80.1 tolerances for power, axis, add, and prism before the patient receives them.
Question 7: If a lensometer shows 1.5 prism diopters of unwanted vertical prism in a pair of glasses, the most likely cause is:
- Incorrect base curve on the lens
- Optical centers being displaced vertically in opposite directions (OC heights not matching) (Correct answer)
- Incorrect temple length on the frame
- The lens material having a different refractive index than ordered
Correct answer: Optical centers being displaced vertically in opposite directions (OC heights not matching)
Unwanted vertical prism is most commonly caused by the optical centers being at different heights in the two lenses, inducing differential prismatic effect at the visual axis.
ABO NOCE Basic Opticianry Dispensing Instrumentation 5
If a lensometer reading shows the sphere drum at +2.00 and the cylinder drum at +0.75 at axis 90, the lens power in minus-cylinder form is: