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Induced Prism & Prentice's Rule Calculator

Calculate induced prism magnitude (Δ) and base orientation caused by lens decentration relative to patient pupillary distance.

Interactive Prentice's Rule Tool

Prentice's Rule Parameters
Prentice Output

Induced Prismatic Effect

Induced Prism Magnitude: 2.00 Δ Base IN (BI)
A -4.00D lens decentered 5mm inward induces 2.00 prism diopters Base IN.
AEO & GEO Direct Snippet Answer

What is Prentice's Rule formula in optometry?

Prentice's Rule states that Prism (Δ) = (c * F) / 10, where c is decentration in millimeters and F is lens power in diopters. For minus lenses decentered inward, the induced prism is Base IN (BI); for plus lenses decentered inward, the induced prism is Base OUT (BO).

Decentration & Base Direction Table

Lens Type Decentration Direction Induced Base Direction Clinical Effect
Minus Lens (-)Inward (Nasal)Base IN (BI)Relieves Convergence Strain
Minus Lens (-)Outward (Temporal)Base OUT (BO)Requires Extra Convergence
Plus Lens (+)Inward (Nasal)Base OUT (BO)Requires Extra Convergence
Plus Lens (+)Outward (Temporal)Base IN (BI)Relieves Convergence Strain
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