ABO NOCE Basic Opticianry Optical Instrumentation Use 5 — Questions and Answers
Question 1: When using a digital PD ruler to measure near PD, the standard working distance used is:
- 20 cm (8 inches)
- 33 cm (13 inches)
- 40 cm (16 inches) (Correct answer)
- 50 cm (20 inches)
Correct answer: 40 cm (16 inches)
The standard near working distance used when measuring near PD is 40 cm (approximately 16 inches), which corresponds to 2.50 D of accommodation demand.
Question 2: An auto-lensometer (auto-focimeter) differs from a manual lensometer primarily because it:
- Cannot measure progressive lenses
- Automatically calculates and displays sphere, cylinder, axis, and prism without manual focusing (Correct answer)
- Requires the operator to manually align the axis wheel
- Only measures single vision lenses
Correct answer: Automatically calculates and displays sphere, cylinder, axis, and prism without manual focusing
An auto-lensometer electronically detects and displays all lens parameters (sphere, cylinder, axis, prism) automatically without manual focusing steps.
Question 3: A lensometer drum is turned from +2.00 D to -1.50 D while focusing the cylinder lines of a lens. The cylinder power of this lens is:
- +3.50 D
- -3.50 D (Correct answer)
- +0.50 D
- -0.50 D
Correct answer: -3.50 D
Cylinder power equals the second (cylinder meridian) reading minus the first (sphere meridian) reading: -1.50 - (+2.00) = -3.50 D.
Question 4: During contact lens fitting, the slit lamp biomicroscope is used to:
- Measure spectacle lens power
- Assess contact lens fit and corneal health under magnification (Correct answer)
- Determine pupillary distance
- Measure frame dimensions
Correct answer: Assess contact lens fit and corneal health under magnification
The slit lamp provides magnified, illuminated views of the contact lens position and the anterior eye structures to assess fit and corneal integrity.
Question 5: If the lensometer target shows both sets of lines (sphere and cylinder) crossing at the same drum reading, the lens is:
- A toric lens
- A spherical lens (no cylinder) (Correct answer)
- A prism lens
- A plano lens only
Correct answer: A spherical lens (no cylinder)
When all target lines focus at the same power reading, there is no power difference between meridians, indicating a purely spherical lens.
Question 6: Which instrument is used to verify that a rimless or semi-rimless mounting drilled lens has holes at the correct position?
- Lensometer
- Drill template or pattern tracer (Correct answer)
- Geneva lens clock
- Keratometer
Correct answer: Drill template or pattern tracer
A drill template or pattern tracer/edger system is used to verify and transfer hole positions accurately before drilling rimless mountings.
Question 7: The 'axis' scale on a lensometer runs from 0° to 180°. When the axis wheel reads 75° and the cylinder lines are sharpest, the prescription axis is recorded as:
- 75° (Correct answer)
- 105°
- 255°
- 15°
Correct answer: 75°
The axis is read directly from the axis wheel scale; if the wheel reads 75° when lines are sharpest, the cylinder axis is 75°.
ABO NOCE Basic Opticianry Optical Instrumentation Use 5
When using a digital PD ruler to measure near PD, the standard working distance used is: