NOCE Dispensing and Fitting Procedures 5 — Questions and Answers
Question 1: What is the recommended minimum fitting height for most progressive addition lenses?
- 14 mm
- 18 mm (Correct answer)
- 22 mm
- 26 mm
Correct answer: 18 mm
Most standard progressive lenses require a minimum fitting height of 18 mm to accommodate the full corridor length and reading zone.
Question 2: A dispensing optician measures a patient's distance PD as 66 mm and near PD as 62 mm. The difference indicates:
- Measurement error that should be repeated
- Normal convergence of approximately 2 mm per eye at near (Correct answer)
- The patient has a significant phoria
- The frame is too wide for the patient
Correct answer: Normal convergence of approximately 2 mm per eye at near
Eyes converge when viewing near objects, so near PD is typically 4–6 mm less than distance PD, representing approximately 2 mm per eye.
Question 3: When using a frame heater (hot air or salt pan) to adjust a plastic frame, the frame should be:
- Heated until the plastic begins to whiten, then bent immediately
- Heated evenly until pliable, then adjusted and held until cooled (Correct answer)
- Immersed in boiling water for 60 seconds without touching
- Heated only at the hinge area to avoid warping the front
Correct answer: Heated evenly until pliable, then adjusted and held until cooled
The frame should be heated evenly until the plastic becomes pliable, then adjusted and held in the new position until it cools to retain the shape.
Question 4: Which verification step checks that prism has not been unintentionally introduced into a finished lens?
- Checking the cylinder axis with a protractor
- Locating the optical center with a lensometer and comparing to the expected position (Correct answer)
- Measuring center thickness with a thickness gauge
- Inspecting the lens for surface defects under magnification
Correct answer: Locating the optical center with a lensometer and comparing to the expected position
Locating the optical center with the lensometer confirms it is positioned where specified; a displaced OC introduces unwanted prism.
Question 5: A patient's new glasses cause a 'floor tilt' perception when walking. This is MOST commonly associated with:
- Too much wrap angle in the frame
- Adaptive difficulty with a progressive lens corridor (Correct answer)
- Incorrect sphere power in the distance zone
- Frame that is too heavy
Correct answer: Adaptive difficulty with a progressive lens corridor
The 'swimming' or floor-tilt perception is a classic adaptation symptom for new progressive lens wearers as the brain adjusts to peripheral distortion zones.
Question 6: According to ANSI Z80.1, what is the maximum allowable horizontal prism imbalance between the two lenses at the distance reference point?
- 0.33 Δ
- 0.67 Δ (Correct answer)
- 1.00 Δ
- 1.33 Δ
Correct answer: 0.67 Δ
ANSI Z80.1 allows a maximum of 0.67 prism diopters of horizontal imbalance between the two lenses at the distance reference point.
Question 7: A patient's frame is sitting too low on the face, causing them to look through the top of the progressive reading zone in distance gaze. The BEST adjustment is to:
- Increase pantoscopic tilt
- Tighten the nose pads to raise the frame (Correct answer)
- Widen the nose pads to lower vertex distance
- Adjust the temple bend further forward
Correct answer: Tighten the nose pads to raise the frame
Tightening (narrowing) the nose pads raises the frame on the patient's face, restoring proper optical center alignment with the pupil.
NOCE Dispensing and Fitting Procedures 5
What is the recommended minimum fitting height for most progressive addition lenses?