Lensometry and Spectacle Lens Verification Flashcards
7 cards from real CPO practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Lensometry and Spectacle Lens Verification flashcards as text
The optical center of a spectacle lens is the point where:
Answer: Light passes through without any prismatic deviation
The optical center is the specific point on a lens through which light travels in a straight line without being deflected by prism.
The power drum on a manual lensometer is calibrated in which unit?
Answer: Diopters (D)
The lensometer power drum is calibrated directly in diopters, allowing the technician to read lens power without conversion.
When performing lensometry on a tinted (sunglass) spectacle lens, the recommended approach is to:
Answer: Increase the lensometer's illumination intensity and proceed normally
Increasing the lensometer's internal illumination compensates for light absorbed by the tint, allowing the mires to remain visible for accurate measurement.
According to ANSI Z80.1 standards, the acceptable tolerance for add power in a finished bifocal spectacle lens is:
Answer: ±0.12 D
ANSI Z80.1 specifies a tolerance of ±0.12 D for add power; a discrepancy greater than this requires the lenses to be returned to the laboratory for remake.
A patient's prescription includes 2Δ base-out for each eye. When verifying with the lensometer, you would expect the mire target to be displaced:
Answer: Toward the nasal (inner) edge of each lens
Base-out prism has its base (thick edge) toward the temporal side, causing the mire target to appear displaced toward the nasal side — opposite the base direction.
The vernier scale on a manual lensometer axis wheel allows the technician to read the cylinder axis to the nearest:
Answer: 1 degree
The vernier scale on the axis wheel provides a precision reading to the nearest 1 degree, which is the clinically required accuracy for most spectacle prescriptions.
When documenting lensometry findings for a finished pair of spectacles, the technician should record findings as:
Answer: Separate sphere, cylinder, and axis values for each eye, with any prism noted
Complete lensometry documentation requires recording sphere, cylinder, and axis for each eye independently, plus any prism found, so results can be compared directly to the written prescription.