Enter the power of the lens and the distance from the optical center into the calculator to determine the prismatic effect. This calculator can also evaluate any of the variables given the others are known.

## Prentice’s Rule Formula

The following formula is used to calculate the prismatic effect according to Prentice’s Rule.

PE = P * d

Variables:

- PE is the prismatic effect (Δ)
- P is the power of the lens (diopters)
- d is the distance from the optical center of the lens (centimeters)

To calculate the prismatic effect, multiply the power of the lens in diopters by the distance from the optical center of the lens in centimeters. This will give the amount of prism induced by the lens, which can be used to ensure that eyeglasses are properly fitted to avoid unwanted prismatic effects.

## What is a Prentice’s Rule?

Prentice’s Rule is a mathematical formula used in optometry and ophthalmology to calculate the prismatic effect of eyeglasses. The rule states that the amount of prism induced by a lens is equal to the power of the lens in diopters multiplied by the distance from the optical center of the lens in centimeters. This rule is used to ensure that eyeglasses are properly fitted to avoid unwanted prismatic effects, which can cause eye strain and other visual disturbances.

## How to Calculate Prentice’s Rule?

The following steps outline how to calculate the Prismatic Effect using Prentice’s Rule.

- First, determine the power of the lens (P) in diopters.
- Next, determine the distance from the optical center of the lens (d) in centimeters.
- Next, gather the formula from above = PE = P * d.
- Finally, calculate the Prismatic Effect (PE).
- After inserting the variables and calculating the result, check your answer with the calculator above.

**Example Problem : **

Use the following variables as an example problem to test your knowledge.

Power of the lens (P) = 2 diopters

Distance from the optical center of the lens (d) = 5 centimeters