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
Which instrument provides a topographic map of the entire corneal surface rather than just central curvature readings?
Answer: Corneal topographer
Corneal topographers use Placido disc reflection or Scheimpflug imaging to map thousands of points across the entire corneal surface, unlike a keratometer which measures only four central points.
When using a lensometer on a trifocal lens, the intermediate add power is calculated as:
Answer: Half of the total add, measured at the intermediate segment
The intermediate segment of a trifocal is measured directly through the lensometer, and its power (typically half of the full add) is read at that specific zone.
An auto-refractor provides an objective refractive measurement by:
Answer: Analyzing retinal reflection patterns from projected infrared light
Auto-refractors project infrared light onto the retina and analyze the reflected wavefront to objectively determine the eye's refractive error.
The ANSI Z80.1 standard specifies that for a single-vision distance lens with a power of -5.00 D, the maximum allowable cylinder power error is:
Answer: ±0.13 D
ANSI Z80.1 allows a cylinder tolerance of ±0.13 D for lenses with sphere powers between ±3.25 D and ±6.50 D.
When using a lensometer to verify prism, the amount of prism is measured by:
Answer: How far the target mires are displaced from the center of the reticle in prism diopters
Prism is measured by how far the target is displaced from the optical center of the lensometer reticle, with each unit of displacement corresponding to one prism diopter.
A lensmeter reading on a right lens shows: -2.00 -1.00 x 180. The dot is marked and the lens is flipped to measure the left lens, which reads -2.00 -1.00 x 180. This indicates the prescription is:
Answer: Correct — axis 180 is the same for all orientations
Axis 180 is a horizontal axis and is the same value whether measured from the right or left lens; it does not mirror like oblique axes do.
Which of the following best describes the purpose of a lens clock (Geneva lens measure) in the opticianry workflow?
Answer: To estimate lens surface curvature and check lens form for remake decisions
A Geneva lens measure estimates surface curvature to help identify lens form and check whether a lens matches the intended base curve, useful in remake verification and lens identification.