NOCE Dispensing and Fitting Procedures 3 — Questions and Answers
Question 1: Which ANSI Z80.1 tolerance applies to the spherical power of a finished ophthalmic lens with a prescription of -4.00 D sphere?
- ±0.06 D
- ±0.13 D (Correct answer)
- ±0.25 D
- ±0.50 D
Correct answer: ±0.13 D
ANSI Z80.1 allows ±0.13 D tolerance for spherical powers between -3.375 D and -6.375 D.
Question 2: A patient with anisometropia requires the optical centers of the lenses to be at different heights. This is best described as:
- Compensatory prism
- Differential vertical decentration
- Slab-off correction (Correct answer)
- Horizontal prism balance
Correct answer: Slab-off correction
Slab-off (or reverse slab-off) grinds prism into the reading zone of one lens to equalize the vertical imbalance caused by anisometropia.
Question 3: During frame selection, you notice a patient has a very narrow nose bridge. Which frame feature should you prioritize?
- Wide keyhole bridge
- Adjustable nose pads on pad arms (Correct answer)
- Saddle bridge with low DBL
- Skull temples with tight bend
Correct answer: Adjustable nose pads on pad arms
Adjustable nose pads on pad arms allow precise customization to fit a narrow nasal bridge securely and comfortably.
Question 4: When fitting a bifocal lens, the standard placement for the flat-top segment top is:
- 5 mm above the lower limbus
- At the lower limbus of the eye (Correct answer)
- 2 mm below the center of the pupil
- At the visual midline of the lens
Correct answer: At the lower limbus of the eye
The standard flat-top bifocal segment top is placed at the lower limbus so it is accessible in downgaze without disrupting distance vision.
Question 5: A patient experiences swim and distortion when wearing new progressive lenses. Which adjustment is MOST likely to help?
- Increase vertex distance
- Adjust pantoscopic tilt to match the prescribed value (Correct answer)
- Replace lenses with a different brand
- Reduce the temple spread
Correct answer: Adjust pantoscopic tilt to match the prescribed value
Correcting pantoscopic tilt aligns the progressive lens zones to the patient's line of sight, reducing peripheral swim and distortion.
Question 6: What does the term 'effective diameter' (ED) mean in lens ordering?
- The actual measured diameter of the finished lens blank
- The smallest circle that encloses the entire frame aperture (Correct answer)
- The distance from the optical center to the furthest frame edge
- The thickness of the lens at the optical center
Correct answer: The smallest circle that encloses the entire frame aperture
Effective diameter is the diameter of the smallest circle that circumscribes the frame aperture, used to determine the minimum blank size needed.
Question 7: Which condition describes lenses that are not level with each other in the finished frame?
- Pantoscopic tilt
- Lens torsion
- Optical center height error
- Frame unleveling or tilt (Correct answer)
Correct answer: Frame unleveling or tilt
Frame unleveling (tilt) means one side of the frame front is higher than the other, causing the lenses to be at different heights relative to the eyes.
NOCE Dispensing and Fitting Procedures 3
Which ANSI Z80.1 tolerance applies to the spherical power of a finished ophthalmic lens with a prescription of -4.00 D sphere?