Calculators
Each calculator has its own page you can bookmark. Every result shows its work.
Contact lenses
- Toric lens over-refractionOrder the next soft toric from its rotation and an over-refraction.LARS, then crossed-cylinder sum
- Back vertex powerSpectacle Rx to the power needed at the cornea (vertex distance compensation).Fc = F / (1 − d·F), each meridian
- Diopters ↔ radius conversionK readings and base curves, either direction, any index.r = (n − 1) / F