Optical Instrumentation Use Flashcards

When using a lensometer to measure a bifocal add power, where should the bifocal segment be positioned in the instrument?

Answer: The reading segment is placed in the aperture ring

To measure add power, the reading (near) segment is placed in the lensometer aperture ring to read the near prescription.

A keratometer reading shows 44.00 D @ 180 and 46.50 D @ 090. What is the corneal cylinder?

Answer: 2.50 D

Corneal cylinder is the difference between the two principal meridian readings: 46.50 - 44.00 = 2.50 D.

Which instrument is used to measure the interpupillary distance (PD) electronically and digitally?

Answer: Pupillometer

A pupillometer is the instrument specifically designed to measure interpupillary distance, often digitally.

When neutralizing a lens with a lensometer, the power wheel is adjusted until the target mires are sharp and at the center. What does this indicate?

Answer: The sphere power has been measured

When the target is centered and clear with the power drum adjusted, the sphere power (or one principal meridian) of the lens has been neutralized.

A radiuscope is primarily used to measure which property of a contact lens?

Answer: Base curve radius

The radiuscope measures the base curve (back central radius) of rigid contact lenses.

When using a Geneva lens clock (lens measure) on a plus lens, what do the pins indicate?

Answer: The center pin is depressed below the outer pins

On a plus lens, the curved surface pushes the center pin inward (down), indicating positive (convex) curvature.

Which of the following prism diopter base directions would be indicated by a lensometer when the mire target is displaced superiorly from the optical center?

Answer: Base down

When the target shifts superiorly in the lensometer eyepiece, it indicates base-down prism in the lens.