ABO NOCE Basic Opticianry Dispensing Instrumentation Questions and Answers 4 — Questions and Answers
Question 1: When verifying a prism prescription with a lensometer, the prism amount is read by:
- Rotating the axis wheel until the target lines separate
- Observing how far the target is displaced from the reticle center in prism diopters (Correct answer)
- Subtracting the near power from the distance power
- Reading the difference between the two lens drum positions
Correct answer: Observing how far the target is displaced from the reticle center in prism diopters
Prism is measured by decentering the lens until the target centers, with the displacement from center indicating the prism power in prism diopters.
Question 2: The purpose of a seg height measuring tool or ruler is to:
- Measure optical center height above the frame bottom
- Determine the vertical placement of the bifocal segment relative to the pupil (Correct answer)
- Assess the pantoscopic tilt of the frame
- Verify the add power of a progressive lens
Correct answer: Determine the vertical placement of the bifocal segment relative to the pupil
A seg height tool measures the distance from the segment top to the lowest part of the frame to ensure proper bifocal placement for the patient.
Question 3: Which of the following best describes the function of a Geneva lens clock on a minus-powered meniscus lens?
- It measures the prism induced by decentration
- It measures both front and back surface curvatures to derive the base curve (Correct answer)
- It measures the optical center thickness directly
- It measures the vertex distance of the lens
Correct answer: It measures both front and back surface curvatures to derive the base curve
The Geneva lens clock measures the sag of each surface separately; by knowing the lens index, the front and back curves can confirm the base curve selection.
Question 4: Frame pantoscopic tilt is measured using a:
- Pupillometer
- Frame protractor or frame aligner with degree markings (Correct answer)
- Geneva lens clock
- Thickness caliper
Correct answer: Frame protractor or frame aligner with degree markings
A frame protractor or frame aligner with degree scale measures how many degrees the frame front is tilted forward from the vertical plane.
Question 5: A lensometer target that shows a starburst or radiating spoke pattern when the lens is placed on the stage most likely indicates:
- A correctly centered spherical lens
- Lens warpage, aberrations, or a highly irregular lens surface (Correct answer)
- High prism in the lens
- An accurately made progressive lens
Correct answer: Lens warpage, aberrations, or a highly irregular lens surface
Irregular or distorted target patterns suggest the lens has surface irregularities, warpage, or optical defects rather than a clean prescription.
Question 6: The effective diameter of a frame is determined by measuring:
- The horizontal visible iris diameter of the patient
- The longest chord through the geometric center of the lens opening (Correct answer)
- The distance from bridge to end piece
- The vertical height of the lens at the optical center
Correct answer: The longest chord through the geometric center of the lens opening
The effective diameter (ED) is the longest chord across the lens shape through its geometric center, used for minimum blank size calculations.
Question 7: Axis determination on the lensometer is most accurate when the dispenser:
- Rotates the drum until both lines focus simultaneously
- Rotates the axis wheel until one set of lines is sharpest, then reads the axis scale (Correct answer)
- Uses the ink marker first and then neutralizes
- Adjusts the eyepiece diopter to compensate for the prescription
Correct answer: Rotates the axis wheel until one set of lines is sharpest, then reads the axis scale
Accurate axis reading requires rotating the axis wheel to sharpen one focal line completely before noting the axis value on the scale.
ABO NOCE Basic Opticianry Dispensing Instrumentation Questions and Answers 4
When verifying a prism prescription with a lensometer, the prism amount is read by: