Optical Instrumentation Usage Flashcards
7 cards from real NOCE 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 Usage flashcards as text
When using a Burton lamp (UV lamp) to inspect contact lenses with fluorescein, a dark (black) area under a rigid contact lens indicates:
Answer: Bearing or touch between the lens and cornea
A dark area under a rigid lens during fluorescein evaluation indicates lens-to-cornea touch or bearing, where fluorescein is displaced by contact pressure.
A pachymeter instrument is used to measure:
Answer: Corneal thickness
A pachymeter measures corneal thickness, which is important for contact lens fitting and monitoring corneal health.
When using a Geneva lens measure on a minus lens, the gauge pointer deflects:
Answer: In the negative direction
A minus (concave) lens surface causes the center pin of the Geneva lens measure to be pushed back, resulting in a negative (minus) reading.
A prismatic effect found at the optical center of a lens during lensometry most likely indicates:
Answer: A manufacturing defect or incorrect prism in the prescription
Prism measured at the optical center of the lens indicates either intentional prescribed prism or a manufacturing error, since a properly made non-prism lens should have zero prism at its optical center.
The slit lamp biomicroscope is used in optical practice primarily to:
Answer: Examine the fit and position of contact lenses on the eye
The slit lamp allows the optician or practitioner to examine contact lens centration, movement, edge lift, and fit characteristics under high magnification.
What does the term 'vertex power' refer to when measured by a lensometer?
Answer: The back vertex power, which is the reciprocal of the back focal length
Back vertex power, as measured by a lensometer, is the reciprocal of the distance from the back surface of the lens to its secondary focal point.
When a spectacle prescription exceeds ±4.00 D in sphere power, back vertex distance becomes clinically significant because:
Answer: Small changes in vertex distance produce meaningful changes in effective lens power
At higher powers, the effective power of the lens at the corneal plane changes significantly with small shifts in vertex distance, requiring compensation during dispensing.