Prism Diopter Calculator

Calculate prism diopters from measured displacement and distance. Uses the standard prism diopter definition and Prentice's rule.

Displacement

Distance

Tab to move between fields

Prism Diopters (Δ)

1 Δ

Deviation Angle0.57°

Direction (1=Standard)1

How to Use This Calculator

Measure the Displacement — how far the image or light is shifted in centimeters at the measurement plane.
Enter the Distance from the prism or lens to the measurement plane in centimeters (100 cm = 1 meter is standard).
The calculator applies the prism diopter formula: Δ = displacement × 100 / distance.
Review the Prism Diopters (Δ) result and Deviation Angle in degrees.
Use the result to specify prism prescription, evaluate strabismus deviation, or verify Prentice's rule for decentered lenses.

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Formula

Prism Diopters (Δ) = displacement(cm) × 100 / distance(cm)

Adjust lens power when changing the vertex distance (e.g., from glasses to contacts or between different frame positions).

Estimate center and edge thickness of eyeglass lenses based on prescription power, lens index, and frame size.

Convert your glasses prescription to contact lens prescription using vertex distance adjustment for powers above ±4D.

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