COT Optics and Lensometry 3

Question 1

What is the add power of a bifocal if the distance power is -2.00 sph and the near power reads -0.50 sph?

Accepted Answer

+1.50 D

Answer

Add power = near power minus distance power: (-0.50) - (-2.00) = +1.50 D.

Question 2

Which type of lens corrects presbyopia by providing a gradual change in power from distance to near without a visible segment line?

Accepted Answer

Progressive addition lens

Answer

Progressive addition lenses (PALs) provide a corridor of increasing plus power from the distance zone to the near zone with no visible line.

Question 3

What is the focal length of a +4.00 D lens?

Accepted Answer

0.25 meters

Answer

Focal length (f) = 1 / power in diopters = 1 / 4.00 = 0.25 meters.

Question 4

Chromatic aberration in optics occurs because different wavelengths of light are refracted at slightly different angles, causing what visual effect?

Accepted Answer

Color fringing around objects

Answer

Chromatic aberration separates colors at the focal point, producing colored fringes around high-contrast edges.

Question 5

A lens has sphere power of -3.00 D and cylinder power of -1.00 D. What is the power in the meridian of the cylinder axis?

Accepted Answer

-3.00 D

Answer

The cylinder axis meridian carries only the sphere power; the cylinder power is added in the meridian 90° away from the axis.

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