ABO NOCE Basic Opticianry Dispensing Instrumentation Questions and Answers 3 — Questions and Answers
Question 1: Which of the following tools is specifically designed to measure the thickness of a spectacle lens?
- Lensometer
- Lens thickness gauge (caliper) (Correct answer)
- Geneva lens clock
- Pupillometer
Correct answer: Lens thickness gauge (caliper)
A lens thickness gauge or caliper directly measures the physical thickness of a lens at any specified point.
Question 2: When using a lensmeter to measure a bifocal lens, the reading through the segment gives the:
- Distance power only
- Near power only (Correct answer)
- Add power only (the difference from distance)
- Prism at the optical center
Correct answer: Near power only
Reading through the bifocal segment on the lensometer yields the total near power; the add power is calculated as near power minus distance power.
Question 3: The marking dots applied by the lensometer's ink marking device indicate the:
- Prism reference point and 180° axis line
- Optical center location and axis orientation (Correct answer)
- Segment optical center of a bifocal
- Near vision zone of a progressive lens
Correct answer: Optical center location and axis orientation
The three dots marked by the lensometer's marker show the optical center (center dot) and the horizontal reference axis (outer dots) of the lens.
Question 4: A frame aligner (frame alignment tool) is most useful for correcting:
- Barrel distortion in lenses
- Pantoscopic tilt and face-form angle of frames (Correct answer)
- Pupillary distance measurement errors
- Vertex distance of contact lenses
Correct answer: Pantoscopic tilt and face-form angle of frames
Frame aligners allow the dispenser to measure and correct pantoscopic tilt and face-form wrap to ensure proper fit and optical performance.
Question 5: In lensometry, the difference in drum readings between the two focal lines of a cylindrical lens indicates the:
- Sphere power
- Cylinder power (Correct answer)
- Add power
- Prism power
Correct answer: Cylinder power
The numerical difference between the two power drum readings when each focal line is clear represents the cylinder power of the lens.
Question 6: A PD ruler (millimeter rule) is most appropriately used to measure:
- The radius of curvature of the lens back surface
- Monocular and binocular pupillary distances using a reference point (Correct answer)
- The add power of a bifocal segment
- The frame's effective diameter
Correct answer: Monocular and binocular pupillary distances using a reference point
A PD ruler placed across the bridge of the nose allows the dispenser to measure pupillary distances using a corneal reflex or pupil center as a reference.
Question 7: Which instrument would best verify that a finished lens has the correct amount of induced prism?
- Distometer
- Lensometer with prism reticle (Correct answer)
- Geneva lens clock
- Thickness caliper
Correct answer: Lensometer with prism reticle
The lensometer can measure prism power and direction by observing displacement of the target from the center of the reticle.
ABO NOCE Basic Opticianry Dispensing Instrumentation Questions and Answers 3
Which of the following tools is specifically designed to measure the thickness of a spectacle lens?