ABO NOCE Basic Opticianry Applying Prentice's Rule 4 — Questions and Answers
Question 1: A compound lens is -3.00 -1.00 × 180. At a point 5 mm below the optical center, what power is used to calculate vertical prism?
- -3.00 D
- -4.00 D (Correct answer)
- -1.00 D
- -3.50 D
Correct answer: -4.00 D
With the cylinder axis at 180°, the cylinder acts fully in the 90° (vertical) meridian, so vertical power = -3.00 + (-1.00) = -4.00 D.
Question 2: Per ANSI Z80.1, what is the maximum allowable induced prism at the MRP for a single-vision lens with power greater than ±3.375 D?
- 1.00Δ
- 0.33Δ
- 0.67Δ (Correct answer)
- 1.50Δ
Correct answer: 0.67Δ
ANSI Z80.1 allows a maximum of 0.67Δ at the MRP for lenses stronger than ±3.375 D due to greater sensitivity to OC displacement.
Question 3: A frame's distance between boxing centers is 70 mm. Patient binocular PD is 62 mm. Lens power is -2.00 D; decentration is split equally. What prism is induced per eye?
- 0.40Δ
- 0.80Δ (Correct answer)
- 1.60Δ
- 0.16Δ
Correct answer: 0.80Δ
Total decentration = 70 - 62 = 8 mm; per eye = 4 mm = 0.4 cm; Δ = 2.00 × 0.4 = 0.80Δ per eye.
Question 4: Which of the following produces the MOST induced prism?
- +1.00 D decentered 10 mm (1.00Δ)
- -3.00 D decentered 5 mm (1.50Δ) (Correct answer)
- +5.00 D decentered 2 mm (1.00Δ)
- +2.00 D decentered 4 mm (0.80Δ)
Correct answer: -3.00 D decentered 5 mm (1.50Δ)
Δ = 3.00 × 0.5 = 1.50Δ, which is greater than any other option listed.
Question 5: A patient wears OD +4.00 D and OS plano. The OD is decentered 4 mm outward. How much horizontal prism imbalance exists between the two eyes?
- 0Δ
- 0.80Δ
- 1.60Δ (Correct answer)
- 4.00Δ
Correct answer: 1.60Δ
OD: Δ = 4.00 × 0.4 = 1.60Δ; plano OS produces 0Δ regardless of decentration; total imbalance = 1.60Δ.
Question 6: If both lens power and decentration are doubled, what happens to the induced prism per Prentice's Rule?
- Prism doubles
- Prism stays the same
- Prism quadruples (Correct answer)
- Prism halves
Correct answer: Prism quadruples
Δ = P × d; doubling both gives (2P)(2d) = 4Pd, so prism quadruples.
Question 7: A patient's near PD is 58 mm but the frame OC distance is 64 mm. With a +2.50 D add, what total base-in prism is induced at near (both eyes combined)?
- 0.75Δ BI total
- 1.50Δ BI total (Correct answer)
- 3.00Δ BI total
- 0.75Δ BO total
Correct answer: 1.50Δ BI total
Per eye decentration = 3 mm = 0.3 cm; Δ = 2.50 × 0.3 = 0.75Δ BI per eye; both eyes same direction so total = 1.50Δ BI.
ABO NOCE Basic Opticianry Applying Prentice's Rule 4
A compound lens is -3.00 -1.00 × 180.
At a point 5 mm below the optical center, what power is used to calculate vertical prism?