ABO NOCE Basic Opticianry Optical Instrumentation Use 4 — Questions and Answers
Question 1: On a lensometer, what does the drum reading indicate when the target lines are sharpest and the axis is at 45°?
- Sphere power at 45°, cylinder axis at 135°
- The cylinder power at axis 45° (Correct answer)
- Prism base at 45°
- The lens add power
Correct answer: The cylinder power at axis 45°
When lines are sharpest with the axis wheel at 45°, the cylinder axis of the lens is 45°, and the drum reading gives the cylinder power.
Question 2: A Geneva lens clock placed on a flat (plano) surface should read:
- +0.50 D
- 0.00 D (Correct answer)
- -0.50 D
- +1.00 D
Correct answer: 0.00 D
A properly calibrated Geneva lens clock reads 0.00 D on a flat surface, confirming the instrument is zeroed correctly.
Question 3: When using a pupillometer for a patient with a significant facial asymmetry, which measurement mode provides the most accurate optical center placement?
- Binocular PD measurement
- Monocular PD measurement from the center of the nose (Correct answer)
- Distance PD only
- Near PD only
Correct answer: Monocular PD measurement from the center of the nose
Monocular PD measurement references each eye independently from the nasal bridge, providing the most accurate placement for asymmetrical faces.
Question 4: What is the function of the ink marker on a lensometer?
- To mark the optical center and axis on the lens surface (Correct answer)
- To indicate the add power on a PAL
- To measure prism amount
- To set the cylinder axis
Correct answer: To mark the optical center and axis on the lens surface
The ink marker dots the lens surface through the lensometer stage, indicating the optical center and reference axis on the lens.
Question 5: To verify the add power of a bifocal lens, a technician reads the distance power first, then repositions the lens to read the near segment. The add power equals:
- Near power minus distance power (Correct answer)
- Distance power minus near power
- The sum of both readings
- Half the near power
Correct answer: Near power minus distance power
Add power = near (segment) power − distance power; this difference represents the additional plus power of the reading segment.
Question 6: A keratometer (ophthalmometer) measures:
- Spectacle lens surface power
- The curvature of the anterior cornea (Correct answer)
- Intraocular pressure
- Pupil diameter
Correct answer: The curvature of the anterior cornea
A keratometer measures the radius of curvature (or power in diopters) of the anterior corneal surface, used in contact lens fitting.
Question 7: When reading a lens on the lensometer and the dot (intersection point) falls to the right of center (toward 180°), which prism direction is indicated?
- Base up
- Base down
- Base in (for right lens) (Correct answer)
- Base out (for right lens)
Correct answer: Base in (for right lens)
A dot displaced toward 180° (nasally for a right lens) indicates base-in prism, as the base is toward the direction of displacement.
ABO NOCE Basic Opticianry Optical Instrumentation Use 4
On a lensometer, what does the drum reading indicate when the target lines are sharpest and the axis is at 45°?