Ophthalmic Lenses and Materials 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 Ophthalmic Lenses and Materials flashcards as text
Which anti-reflective coating residual color is most commonly seen on AR-coated lenses?
Answer: Blue/green or purple/green
Most AR coatings are designed to have a blue-green or purple-green residual reflex, which is the color of light reflected off the coated surface when viewed at an angle.
What does 'index of refraction' measure in an ophthalmic lens material?
Answer: The ratio of light speed in a vacuum to light speed in the material
Index of refraction (n) is the ratio of the speed of light in a vacuum to its speed in the material; a higher index means light slows more, allowing the lens to be made thinner.
A patient is prescribed a +2.00 add in their progressive lenses. Where does the corridor (channel) connect the distance and near zones?
Answer: Through the intermediate zone between the distance and near reference points
The corridor or channel of a PAL is a narrow zone of increasing power connecting the distance zone (top) to the near zone (bottom), passing through the intermediate zone for arm's-length vision.
Which lens form (design) provides the best optical performance by minimizing off-axis aberrations?
Answer: Best form (corrected curve or Tscherning ellipse curve)
Best form lenses use the Tscherning ellipse to select front curves that minimize oblique astigmatic error for a given prescription power, providing superior peripheral optical performance.
When verifying a progressive addition lens on a lensometer (focimeter), what is the standard method for locating the distance reference point?
Answer: Place the dot-marked fitting cross under the lensometer stop and read the power there
The manufacturer's markings (temporary dots, engravings, or fitting cross) on a PAL identify the distance reference point; placing the fitting cross under the lensometer stop gives the distance prescription reading.
What is the purpose of a 'lenticular' lens design?
Answer: To reduce weight and thickness in very high-power prescriptions by limiting the full-power zone to a central optical cap
Lenticular lenses have a central optical portion (the lenticular bowl or cap) containing the full prescription power, surrounded by a carrier of reduced power, dramatically reducing weight and thickness for very high prescriptions.
Which statement BEST describes the relationship between lens power and center thickness for a minus lens?
Answer: Higher minus power allows thinner center thickness but produces thicker edges
Minus lenses are thinnest at the center and thickest at the edges; as minus power increases, the center can be made thinner but the edges become progressively thicker.