FREE ABO-NOCE Applying Prentice's Rule Questions and Answers

Question 1

A patient with a prescription of -4.00 DS looks 5 mm above the optical center. How much prism is induced and in what direction?

Accepted Answer

2.0Δ Base Down

Answer

Prentice's Rule is P = cF, where 'c' is in cm. P = (0.5 cm) * (4.00 D) = 2.0Δ. Looking up through a minus lens induces Base Down (BD) prism. This can be remembered with the acronym BUDA: Base Up Down and Away (from the OC).

Question 2

A lens with a power of +6.00 D is decentered 3 mm nasally. What is the resulting prism?

Accepted Answer

1.8Δ Base In

Answer

Using Prentice's Rule: P = cF = (0.3 cm) * (6.00 D) = 1.8Δ. Decentering a plus lens nasally moves the optical center nasally. To look through the OC, the eye would have to turn in, so the prism is Base In (BI).

Question 3

A patient's PD is 64 mm, but their glasses were made with the optical centers at 60 mm. If the Rx is -5.00 DS in both eyes, what is the total induced prism?

Accepted Answer

2.0Δ Base Out

Answer

The total decentration is 4 mm, or 2 mm per eye. The OCs are too narrow, so they are decentered nasally. P = cF = (0.2 cm) * (5.00 D) = 1.0Δ per eye. For a minus lens, nasal decentration creates Base Out prism. The total is 1.0Δ BO + 1.0Δ BO = 2.0Δ BO.

Question 4

How much must a -10.00 D lens be decentered to produce 3.0Δ of prism?

Accepted Answer

3 mm

Answer

Rearranging Prentice's Rule gives c = P / F. So, c = 3.0Δ / 10.00 D = 0.3 cm. To express the answer in millimeters, multiply by 10. 0.3 cm * 10 = 3 mm.

Question 5

A patient with Rx OD: +2.00 DS, OS: +4.00 DS looks 10 mm down to read. What is the vertical imbalance?

Accepted Answer

2.0Δ

Answer

First, calculate the prism for each eye. OD: P = (1.0 cm) * (2.00 D) = 2.0Δ BD. OS: P = (1.0 cm) * (4.00 D) = 4.0Δ BD. Since both bases are in the same direction, the imbalance is the difference between them: 4.0Δ - 2.0Δ = 2.0Δ.

ABO NOCE Basic Opticianry Practice Test

ABO NOCE Basic Opticianry Practice Test

FREE ABO-NOCE Applying Prentice's Rule Questions and Answers