Optical Instrumentation Use Flashcards
7 cards from real ABO NOCE Basic Opticianry practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Optical Instrumentation Use flashcards as text
When measuring the seg height of a bifocal lens in the frame, which instrument is most appropriate?
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.
In a lensometer, what do the three lines in one meridian and a single line in the other meridian represent?
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.
When using a focimeter (lensometer) to verify a lens power of -3.00 -1.25 × 090, which set of lines do you focus first?
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.
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:
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.
Which of the following best describes the purpose of the axis wheel on a lensometer?
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.
A vertex distance of 14 mm is standard for many prescriptions. Which instrument directly measures vertex distance?
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.
When performing hand neutralization of an unknown lens and the image moves 'against' (opposite to lens movement), the lens is:
Answer: Plus (convex)
A plus (convex) lens produces 'against' movement (the image moves opposite to the direction of lens movement) during hand neutralization.