Prentice's Rule Prism Calculator
Compute the induced prismatic effect at a point on a spectacle lens from decentration and lens power using Prentice's rule.
How to Use the Prentice's Rule Prism Calculator
- Enter decentration in millimetres.
- Enter lens power in diopters (sign ignored).
- Click Calculate to see induced prism.
Casos de Uso
- •Dispensing optics verification.
- •Binocular vision troubleshooting.
- •Teaching optometric theory.
Fórmula
Δ (prism diopters) = c (cm of decentration) × F (lens power in diopters). 1 cm = 10 mm.
Preguntas Frecuentes
Why does decentration cause prism?
Every point away from the optical centre of a lens behaves like a small prism. Prentice's rule quantifies exactly how much, which matters when the optical centre is not aligned with the pupil.
How much induced prism is acceptable?
Most patients tolerate up to ~0.5 Δ vertically and ~2 Δ horizontally without diplopia. Binocular imbalance above this needs correction.
Medical disclaimer
Educational tool only. Not a substitute for a refraction and binocular vision assessment by a licensed optometrist or ophthalmologist.