Applying Prentice's Rule Flashcards
7 cards from real ABO NOCE Basic Opticianry practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Applying Prentice's Rule flashcards as text
A lens has a power of +3.00 D. A patient's pupil is decentered 4 mm below the optical center. How much vertical prism is induced?
Answer: 1.20Δ base up
Δ = P × d = 3.00 × 0.4 = 1.20Δ; looking below the OC of a plus lens produces base-up prism because the prism base points toward the OC.
Using Prentice's Rule, how much prism is induced when a -5.00 D lens is decentered 6 mm from the optical center?
Answer: 3.00Δ
Δ = P × d = 5.00 × 0.6 cm = 3.00Δ.
A patient requires 2.00Δ of prism. The available lens power is +4.00 D. How far must the lens be decentered to achieve this?
Answer: 5 mm
d = Δ/P = 2.00/4.00 = 0.5 cm = 5 mm.
Which unit for distance (d) must be used in Prentice's Rule formula Δ = P × d?
Answer: Centimeters
Prentice's Rule requires distance in centimeters; using millimeters without converting gives an answer 10 times too large.
A frame PD is 68 mm and the patient's PD is 60 mm. The lens power is +2.50 D. How much horizontal prism is induced per eye if the decentration is split equally?
Answer: 1.00Δ per eye
Total decentration = 8 mm; split = 4 mm = 0.4 cm per eye; Δ = 2.50 × 0.4 = 1.00Δ per eye.
For a -2.00 D lens, the optical center is decentered 10 mm nasally in front of the right eye. What is the prismatic effect and base direction?
Answer: 2.00Δ base out
Δ = 2.00 × 1.0 = 2.00Δ; for a minus lens decentered nasally in the right eye, prism base points toward the decentration = base out.
A bifocal add of +2.50 D has its segment center 3 mm below the add's optical center. What is the vertical prismatic effect at the segment center?
Answer: 0.75Δ base down
Δ = 2.50 × 0.3 = 0.75Δ; looking below the OC of a plus add produces base-down prism.