NOCE Optical Instrumentation Use 3 — Questions and Answers
Question 1: A pachymeter is used in optometry and ophthalmology to measure which ocular structure?
- Intraocular pressure
- Corneal thickness (Correct answer)
- Retinal thickness
- Lens thickness
Correct answer: Corneal thickness
A pachymeter measures corneal thickness, which is important for conditions like glaucoma screening and pre-refractive surgery evaluation.
Question 2: On a manual lensometer, what is the purpose of rotating the eyepiece reticle before beginning a measurement?
- To set the prism reference
- To focus the reticle for the examiner's own eye (Correct answer)
- To align the axis wheel
- To calibrate the power drum
Correct answer: To focus the reticle for the examiner's own eye
Rotating the eyepiece adjusts the reticle to be sharply focused for the individual examiner's eye, correcting for their own ametropia.
Question 3: When measuring a progressive addition lens (PAL) with a lensometer, where on the lens should you place the distance reference mark?
- At the near zone
- At the prism reference point (PRP) or fitting cross (Correct answer)
- At the segment top
- At the temporal periphery
Correct answer: At the prism reference point (PRP) or fitting cross
The prism reference point (PRP) or fitting cross is the standard location for placing a PAL in the lensometer to read distance power.
Question 4: A contact lens thickness gauge (dial gauge) measures which parameter in hundredths of a millimeter?
- Diameter
- Base curve
- Center or edge thickness (Correct answer)
- Optical zone diameter
Correct answer: Center or edge thickness
A contact lens thickness gauge measures center or edge thickness in increments typically of 0.01 mm.
Question 5: When using an auto-refractor, the instrument measures which of the following to determine the refractive error?
- The curvature of the cornea only
- The reflection of an infrared target from the retina (Correct answer)
- The patient's subjective response to lens changes
- The intraocular pressure
Correct answer: The reflection of an infrared target from the retina
Auto-refractors project an infrared target onto the retina and analyze the reflected wavefront to objectively calculate refractive error.
Question 6: The Humphrey lensmeter (automated lensometer) expresses cylinder in which form by default?
- Plus cylinder form only
- Minus cylinder form only
- Both plus and minus, selectable (Correct answer)
- Spherical equivalent only
Correct answer: Both plus and minus, selectable
Most automated lensometers allow the user to select either plus or minus cylinder notation for the displayed prescription.
Question 7: Which instrument would an optician use to verify that a finished spectacle lens has the correct base curve?
- Lensometer
- Pupillometer
- Geneva lens clock (Correct answer)
- Keratometer
Correct answer: Geneva lens clock
A Geneva lens clock (lens measure) measures the surface curvature of a spectacle lens to verify its base curve.
NOCE Optical Instrumentation Use 3
A pachymeter is used in optometry and ophthalmology to measure which ocular structure?