ABO NOCE Basic Opticianry Optical Instrumentation Use Questions and Answers 2 — Questions and Answers
Question 1: When using a lensometer to measure a bifocal lens, where should the segment optical center be placed to read the add power?
- Over the distance optical center
- Over the near segment optical center (Correct answer)
- At the geometric center of the lens
- At the temporal edge of the lens
Correct answer: Over the near segment optical center
The near segment optical center must be placed over the lensometer stop to accurately measure the add power.
Question 2: Which instrument is used to measure the curvature of the front and back surfaces of a contact lens?
- Lensometer
- Keratometer
- Radiuscope (Correct answer)
- Pupillometer
Correct answer: Radiuscope
The radiuscope (also called an ophthalmometer for contact lenses) measures the base curve radius of contact lenses.
Question 3: On a manual lensometer, the power drum is turned until the target lines are sharpest. What does a clear sphere target with blurred lines indicate?
- No cylinder power is present
- Cylinder axis is misaligned
- There is cylinder power present (Correct answer)
- The lens is prismatic
Correct answer: There is cylinder power present
When the sphere lines are clear but cylinder lines remain blurred, cylinder power exists in the lens and needs to be neutralized.
Question 4: A lensometer reading shows that the target does not center in the eyepiece even when the lens is moved horizontally. This indicates the presence of:
- Cylinder power
- Sphere power
- Prism (Correct answer)
- Add power
Correct answer: Prism
Prism causes the target to be displaced from center, and the amount of displacement indicates the prismatic power.
Question 5: What is the purpose of the ink dots placed on a lens after neutralization with a lensometer?
- To mark the optical center and axis (Correct answer)
- To indicate the segment height
- To show the progressive corridor
- To mark the fitting cross
Correct answer: To mark the optical center and axis
The three ink dots mark the optical center and cylinder axis orientation so the lens can be properly edged and positioned in the frame.
Question 6: When measuring progressive addition lenses (PALs) with a lensometer, the distance power is measured:
- Through the near zone
- Through the intermediate zone
- Through the distance zone in the upper portion (Correct answer)
- At the geometric center of the lens
Correct answer: Through the distance zone in the upper portion
The distance power of a PAL is measured through the upper distance zone, where the prescribed distance Rx is located.
Question 7: A Geneva lens clock (lens gauge) measures:
- The refractive index of a lens
- The surface curvature of a lens in diopters (Correct answer)
- The overall lens thickness
- The abbe value of the material
Correct answer: The surface curvature of a lens in diopters
A Geneva lens clock measures the surface curvature of a lens by converting the sag height to approximate diopter values.
ABO NOCE Basic Opticianry Optical Instrumentation Use Questions and Answers 2
When using a lensometer to measure a bifocal lens, where should the segment optical center be placed to read the add power?