NOCE Spectacle Dispensing Procedures 5 — Questions and Answers
Question 1: When dispensing lenses with prescribed prism, the prism reference point (PRP) should be placed:
- At the geometric center of the frame
- At the patient's pupil center in primary gaze (Correct answer)
- At the lower third of the lens
- At the fitting cross of a progressive lens
Correct answer: At the patient's pupil center in primary gaze
The prism reference point must coincide with the patient's pupil in primary gaze so the prescribed prism is fully effective.
Question 2: A patient's complaint of 'ghost images' in a new single vision AR-coated lens most likely indicates:
- Incorrect cylinder power
- Reflections from the back surface not fully suppressed (Correct answer)
- Incorrect sphere power
- Pantoscopic tilt too flat
Correct answer: Reflections from the back surface not fully suppressed
Ghost images in AR-coated lenses are caused by internal reflections—particularly from the back surface—that the coating did not fully eliminate.
Question 3: During frame adjustment, 'X-ing' the temples refers to:
- Crossing the temples behind the head for storage
- A condition where one temple is angled inward and the other outward, causing the frame to sit unevenly (Correct answer)
- Tightening both temples simultaneously
- Bending the temples downward at the ear bend
Correct answer: A condition where one temple is angled inward and the other outward, causing the frame to sit unevenly
X-ing occurs when temples are angled asymmetrically—one in and one out—preventing the frame from lying flat on a table and causing an uneven fit.
Question 4: For a patient with a vertex distance of 14mm measured during the refraction, but the dispensed frame sits at 10mm, lenses with powers greater than ±4.00 D should be:
- Ordered with the same power as the prescription
- Adjusted in power to compensate for the shorter vertex distance (Correct answer)
- Ordered with increased base curve
- Ordered in a larger frame to increase vertex distance
Correct answer: Adjusted in power to compensate for the shorter vertex distance
A change in vertex distance alters the effective power reaching the eye, so lenses stronger than ±4.00 D should be recalculated using the vertex compensation formula.
Question 5: Which ANSI standard specifically governs the optical and physical performance requirements for prescription ophthalmic lenses in the United States?
- ANSI Z87.1
- ANSI Z80.1 (Correct answer)
- ANSI Z80.3
- ANSI Z80.5
Correct answer: ANSI Z80.1
ANSI Z80.1 sets the requirements for prescription ophthalmic lenses including power tolerances, prism tolerances, and optical quality in the US.
Question 6: A patient with convergence insufficiency has been prescribed 2Δ base-in split between both lenses. If this is prescribed as slab-off, which lens receives the slab-off and in what direction?
- Slab-off is not applicable for base-in prism (Correct answer)
- The lens with the more minus power receives slab-off creating base-down effect
- The lens with the more plus power receives slab-off creating base-up effect
- Both lenses receive slab-off to share the prism equally
Correct answer: Slab-off is not applicable for base-in prism
Slab-off is used to resolve vertical imbalance at near in bifocal wearers, not horizontal (base-in/out) prism; base-in prism is ground in or incorporated differently.
Question 7: When using a hand neutralization technique to determine lens power, a 'with' motion of the cross-lines means the lens is:
- Plano
- Minus power
- Plus power (Correct answer)
- Prism only
Correct answer: Plus power
A 'with' motion (target appears to move in the same direction as the lens movement) indicates a plus lens during hand neutralization.
NOCE Spectacle Dispensing Procedures 5
When dispensing lenses with prescribed prism, the prism reference point (PRP) should be placed: