ABO NOCE Basic Opticianry Optical Instrumentation Use 2 — Questions and Answers
Question 1: When using a lensometer to verify a progressive addition lens (PAL), where should the distance zone reading be taken?
- At the geometric center of the lens
- At the distance reference point (DRP) marked on the lens (Correct answer)
- At the optical center dot
- At the near reference point
Correct answer: At the distance reference point (DRP) marked on the lens
The distance reference point (DRP) is the designated location on a PAL where the distance power is verified with the lensometer.
Question 2: A Geneva lens clock (lens measure) reads +2.00 D on the front surface and -0.75 D on the back surface of a lens. What is the approximate through power?
- +2.75 D
- +1.25 D (Correct answer)
- -1.25 D
- +2.00 D
Correct answer: +1.25 D
Through power is approximated by adding the front and back surface powers: +2.00 + (-0.75) = +1.25 D.
Question 3: What does a PD meter (pupillometer) primarily measure?
- The vertex distance from the cornea to the lens
- The interpupillary distance (Correct answer)
- The base curve of the lens
- The prism in a lens
Correct answer: The interpupillary distance
A pupillometer measures the interpupillary distance (PD), which is critical for correctly placing optical centers.
Question 4: When neutralizing a lens with the lensometer, the power rings are brought to sharpest focus and the lines appear broken. This indicates the presence of:
- Prism
- Cylinder (Correct answer)
- Sphere only
- Base curve error
Correct answer: Cylinder
Broken or discontinuous lines in the lensometer eyepiece indicate the presence of cylinder (astigmatism) in the lens.
Question 5: Which instrument is used to measure the base curve of a finished lens?
- Lensometer
- Geneva lens clock (Correct answer)
- Radiuscope
- Focimeter
Correct answer: Geneva lens clock
The Geneva lens clock (lens measure) is used at the dispensing level to measure the surface curves of a finished lens.
Question 6: A lensometer shows that a lens has 1.50 D of prism. If the dot is located below the 90° line, the prism is:
- Base up (Correct answer)
- Base down
- Base in
- Base out
Correct answer: Base up
When the dot (intersection of lines) is displaced below center in the lensometer, the prism is base up in the lens.
Question 7: The radiuscope is used primarily to measure:
- Lens power in diopters
- The radius of curvature of a contact lens back surface (Correct answer)
- Pupillary distance
- Vertex distance
Correct answer: The radius of curvature of a contact lens back surface
The radiuscope measures the radius of curvature of contact lens surfaces, particularly the back (base) curve.
ABO NOCE Basic Opticianry Optical Instrumentation Use 2
When using a lensometer to verify a progressive addition lens (PAL), where should the distance zone reading be taken?