ABO NOCE Basic Opticianry Ophthalmic Lenses and Materials 4

Question 1

Which anti-reflective coating residual color is most commonly seen on AR-coated lenses?

Accepted Answer

Blue/green or purple/green

Answer

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.

Question 2

What does 'index of refraction' measure in an ophthalmic lens material?

Accepted Answer

The ratio of light speed in a vacuum to light speed in the material

Answer

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.

Question 3

A patient is prescribed a +2.00 add in their progressive lenses. Where does the corridor (channel) connect the distance and near zones?

Accepted Answer

Through the intermediate zone between the distance and near reference points

Answer

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.

Question 4

Which lens form (design) provides the best optical performance by minimizing off-axis aberrations?

Accepted Answer

Best form (corrected curve or Tscherning ellipse curve)

Answer

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.

Question 5

When verifying a progressive addition lens on a lensometer (focimeter), what is the standard method for locating the distance reference point?

Accepted Answer

Place the dot-marked fitting cross under the lensometer stop and read the power there

Answer

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.

ABO NOCE Basic Opticianry Practice Test

ABO NOCE Basic Opticianry Practice Test

ABO NOCE Basic Opticianry Ophthalmic Lenses and Materials 4