NOCE Optical Instrumentation Use 2 — Questions and Answers
Question 1: When using a lensometer to measure a bifocal add power, where should the bifocal segment be positioned in the instrument?
- Centered in the aperture ring
- Positioned so the segment line bisects the aperture
- The reading segment is placed in the aperture ring (Correct answer)
- Above the distance optical center
Correct 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.
Question 2: A keratometer reading shows 44.00 D @ 180 and 46.50 D @ 090. What is the corneal cylinder?
- 44.00 D
- 46.50 D
- 2.50 D (Correct answer)
- 90.50 D
Correct answer: 2.50 D
Corneal cylinder is the difference between the two principal meridian readings: 46.50 - 44.00 = 2.50 D.
Question 3: Which instrument is used to measure the interpupillary distance (PD) electronically and digitally?
- Lensometer
- Pupillometer (Correct answer)
- Keratometer
- Radiuscope
Correct answer: Pupillometer
A pupillometer is the instrument specifically designed to measure interpupillary distance, often digitally.
Question 4: 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?
- The axis has been found
- The sphere power has been measured (Correct answer)
- The cylinder power has been measured
- The prism is neutralized
Correct 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.
Question 5: A radiuscope is primarily used to measure which property of a contact lens?
- Diameter
- Center thickness
- Base curve radius (Correct answer)
- Oxygen transmissibility
Correct answer: Base curve radius
The radiuscope measures the base curve (back central radius) of rigid contact lenses.
Question 6: When using a Geneva lens clock (lens measure) on a plus lens, what do the pins indicate?
- The center pin rises above the outer pins
- The center pin is depressed below the outer pins (Correct answer)
- All three pins align at the same level
- The outer pins rise above the center pin
Correct 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.
Question 7: 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?
- Base up
- Base down (Correct answer)
- Base in
- Base out
Correct answer: Base down
When the target shifts superiorly in the lensometer eyepiece, it indicates base-down prism in the lens.
NOCE Optical Instrumentation Use 2
When using a lensometer to measure a bifocal add power, where should the bifocal segment be positioned in the instrument?