Optical Instrumentation Use Questions and Answers 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 Questions and Answers flashcards as text
Which instrument is used to measure the vertex distance between the back surface of a spectacle lens and the front of the cornea?
Answer: Distometer (vertex distance gauge)
A distometer (vertex distance gauge) measures the distance from the posterior lens surface to the anterior cornea, important for high-power prescriptions.
A lensometer target appears as two sets of lines oriented 90 degrees apart. The lines running in one direction clear at +2.00 and those running perpendicular clear at +3.50. What is the prescription?
Answer: +2.00 +1.50 × axis of first clear lines
Starting with the lower power meridian (+2.00) as the sphere, the cylinder is the algebraic difference (+1.50), and the axis aligns with the first set of lines to clear.
What does a seg height measurement represent in opticianry?
Answer: The distance from the bottom of the frame to the pupil center
Seg height is measured from the lowest point of the finished frame to the center of the patient's pupil, determining where the bifocal segment should be placed.
When measuring a plano lens on a lensometer, the target should be:
Answer: Centered and clear when the drum is at zero
A plano (no power) lens does not alter the light path, so the target remains centered and clear when the power drum is set to zero.
The 'mire' in a keratometer refers to:
Answer: The illuminated target pattern projected onto the cornea
Mires are the specific illuminated rings or crosses projected onto the cornea whose reflected images are measured to calculate corneal curvature.
Which of the following would indicate that a lensometer needs recalibration?
Answer: A known plano lens reads a power other than zero
If a verified plano lens does not read zero on the lensometer, the instrument is out of calibration and must be adjusted.
When measuring a lens with the lensometer, moving the lens to the right causes the target to move to the left. This relationship tells you that:
Answer: The lens has minus power
When moving a lens causes the target to move in the opposite direction (against motion), the lens has minus (concave) power.