Optical Instrumentation Use 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 Use flashcards as text
When a lensometer target shows two distinct sets of lines perpendicular to each other that cannot both be brought into focus simultaneously, this indicates the lens has:
Answer: Cylinder (astigmatic) power
Inability to focus two perpendicular line sets simultaneously in a lensometer indicates cylindrical (astigmatic) power in the lens.
On a Bausch & Lomb keratometer (one-position instrument), mire doubling is achieved by which mechanism?
Answer: Adjusting internal prisms or drums
The B&L keratometer uses internal prisms (drums) to double the mire images, allowing measurement in a single instrument position.
When verifying the optical center placement of a finished spectacle lens using a lensometer, the ink dots should be placed while the lens is:
Answer: Placed with the front surface facing the instrument
The lens is placed in the lensometer with the front surface facing the instrument (convex side toward the lens stop) for standard measurement.
A contact lens projection magnifier (shadowgraph) is used to measure which contact lens parameter by projecting an enlarged image?
Answer: Diameter and surface quality
A shadowgraph projects an enlarged shadow image of a contact lens to measure its overall diameter and inspect surface quality or edge defects.
When using a PD ruler to measure monocular PDs, the examiner should close which of their own eyes to eliminate parallax error?
Answer: The eye opposite to the patient's eye being measured
To eliminate parallax, the examiner closes the eye opposite to the patient's eye being measured, so their open eye is aligned over the measurement point.
Which lensometer reading sequence is the correct method for measuring a lens in minus cylinder form?
Answer: Focus the line target for the most plus power, record as sphere; rotate axis to focus lines for least plus power, record cylinder as the difference
In minus cylinder form, start with the most plus (least minus) power meridian for the sphere, then rotate 90° to the other meridian; the difference between the two readings is the cylinder.
An optical coherence tomographer (OCT) used in an ophthalmic setting produces cross-sectional images using which principle?
Answer: Infrared light interferometry
OCT uses low-coherence infrared light interferometry to produce high-resolution cross-sectional images of ocular structures without contact.