ABO NOCE Basic Opticianry Applying Prentice's Rule 2

Question 1

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?

Accepted Answer

1.20Δ base up

Answer

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.

Question 2

Using Prentice's Rule, how much prism is induced when a -5.00 D lens is decentered 6 mm from the optical center?

Accepted Answer

3.00Δ

Answer

Δ = P × d = 5.00 × 0.6 cm = 3.00Δ.

Question 3

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?

Accepted Answer

5 mm

Answer

d = Δ/P = 2.00/4.00 = 0.5 cm = 5 mm.

Question 4

Which unit for distance (d) must be used in Prentice's Rule formula Δ = P × d?

Accepted Answer

Centimeters

Answer

Prentice's Rule requires distance in centimeters; using millimeters without converting gives an answer 10 times too large.

Question 5

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?

Accepted Answer

1.00Δ per eye

Answer

Total decentration = 8 mm; split = 4 mm = 0.4 cm per eye; Δ = 2.50 × 0.4 = 1.00Δ per eye.

ABO NOCE Basic Opticianry Practice Test

ABO NOCE Basic Opticianry Practice Test

ABO NOCE Basic Opticianry Applying Prentice's Rule 2