ABO NOCE Basic Opticianry Applying Prentice's Rule 3 — Questions and Answers
Question 1: A patient's right eye requires 1.50Δ base in. The lens power is +3.00 D. In which direction and how far should the optical center be decentered?
- 0.5 mm nasally
- 5 mm nasally (Correct answer)
- 5 mm temporally
- 0.5 mm temporally
Correct answer: 5 mm nasally
d = 1.50/3.00 = 0.5 cm = 5 mm; for a plus lens, decentering the OC nasally places the eye temporal to the OC, inducing base-in prism.
Question 2: An optician finds 1.80Δ of induced prism in a -4.50 D lens. How far is the OC displaced from the MRP?
- 4 mm (Correct answer)
- 0.4 mm
- 8.1 mm
- 2.5 mm
Correct answer: 4 mm
d = 1.80/4.50 = 0.4 cm = 4 mm.
Question 3: Which of the following correctly states Prentice's Rule?
- Δ = d / P
- Δ = P × d (d in mm)
- Δ = P × d (d in cm) (Correct answer)
- Δ = P / d (d in cm)
Correct answer: Δ = P × d (d in cm)
Prentice's Rule is Δ = P × d, where d must be in centimeters.
Question 4: A +6.00 D lens is positioned so the patient looks through a point 3 mm above the optical center. What is the induced prism and base direction?
- 1.80Δ base up (Correct answer)
- 1.80Δ base down
- 18.0Δ base up
- 0.18Δ base down
Correct answer: 1.80Δ base up
Δ = 6.00 × 0.3 = 1.80Δ; looking above the OC of a plus lens induces base-up prism because the base is toward the OC.
Question 5: OD is +2.00 D decentered 4 mm temporally; OS is +2.00 D decentered 4 mm temporally. What is the total horizontal prismatic imbalance between the eyes?
- 0Δ
- 0.80Δ
- 1.60Δ (Correct answer)
- 3.20Δ
Correct answer: 1.60Δ
Each eye: Δ = 2.00 × 0.4 = 0.80Δ; OD temporal decentration = base out OD; OS temporal decentration = base out OS; both base out means they compound, creating 1.60Δ total imbalance for vergence.
Question 6: When using Prentice's Rule in a trifocal, which power is used for a point within the intermediate segment?
- Distance power only
- Full near add power only
- Distance power plus intermediate add power (Correct answer)
- Near add power only
Correct answer: Distance power plus intermediate add power
The effective power at any segment zone equals the distance power combined with that segment's add power.
Question 7: A -1.50 D lens is decentered 5 mm temporally for the left eye. What prismatic effect does this create?
- 0.75Δ base in (Correct answer)
- 0.75Δ base out
- 1.50Δ base in
- 0.75Δ base up
Correct answer: 0.75Δ base in
Δ = 1.50 × 0.5 = 0.75Δ; for a minus lens in the left eye decentered temporally, the base points toward the decentration = temporal = base in for the left eye.
ABO NOCE Basic Opticianry Applying Prentice's Rule 3
A patient's right eye requires 1.50Δ base in.
The lens power is +3.00 D.
In which direction and how far should the optical center be decentered?