ABO NOCE Basic Opticianry Optical Instrumentation Use 3 — Questions and Answers
Question 1: When measuring the seg height of a bifocal lens in the frame, which instrument is most appropriate?
- PD ruler and a felt-tip marker dot
- A pupillometer set to monocular mode
- A seg height ruler or millimeter rule referenced from the lower frame rim (Correct answer)
- A lensometer with a dot marker
Correct answer: A seg height ruler or millimeter rule referenced from the lower frame rim
Seg height is measured in millimeters from the bottom of the lens or lower frame rim to the top of the segment, using a millimeter ruler.
Question 2: In a lensometer, what do the three lines in one meridian and a single line in the other meridian represent?
- Prism and no cylinder
- Two power meridians of a toric (cylindrical) lens (Correct answer)
- Bifocal seg power
- Add power only
Correct answer: Two power meridians of a toric (cylindrical) lens
The two sets of lines (three lines and one line) represent the two principal meridians of a toric lens, used to read sphere and cylinder power.
Question 3: When using a focimeter (lensometer) to verify a lens power of -3.00 -1.25 × 090, which set of lines do you focus first?
- The lines running at 180° (the sphere meridian) (Correct answer)
- The lines running at 090° (the cylinder meridian)
- It does not matter; either set can be focused first
- The add power lines
Correct answer: The lines running at 180° (the sphere meridian)
By convention, you first focus the lines running parallel to the cylinder axis to find the sphere power, then rotate to find the cylinder power.
Question 4: A hand neutralization technique uses trial lenses to cancel lens power. If a +2.00 D trial lens fully neutralizes movement, the unknown lens power is:
- +2.00 D
- -2.00 D (Correct answer)
- +4.00 D
- Plano
Correct answer: -2.00 D
A +2.00 D trial lens neutralizes a -2.00 D lens because equal and opposite powers cancel, resulting in no apparent movement.
Question 5: Which of the following best describes the purpose of the axis wheel on a lensometer?
- It adjusts the magnification of the eyepiece
- It rotates the target to align with the cylinder axis (Correct answer)
- It moves the lens stage up and down
- It sets the add power reference
Correct answer: It rotates the target to align with the cylinder axis
The axis wheel rotates the internal target so the lines can be aligned with the cylinder axis meridian of the lens being measured.
Question 6: A vertex distance of 14 mm is standard for many prescriptions. Which instrument directly measures vertex distance?
- PD ruler
- Distometer (vertex distance gauge) (Correct answer)
- Radiuscope
- Geneva lens clock
Correct answer: Distometer (vertex distance gauge)
A distometer (vertex distance gauge) is placed against the closed eyelid or cornea to measure the distance from the cornea to the back surface of the lens.
Question 7: When performing hand neutralization of an unknown lens and the image moves 'against' (opposite to lens movement), the lens is:
- Plano
- Minus (concave)
- Plus (convex) (Correct answer)
- A prism
Correct answer: Plus (convex)
A plus (convex) lens produces 'against' movement (the image moves opposite to the direction of lens movement) during hand neutralization.
ABO NOCE Basic Opticianry Optical Instrumentation Use 3
When measuring the seg height of a bifocal lens in the frame, which instrument is most appropriate?