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Optometry & Ophthalmology Standard Formulas

Prescription Transposition & SE Tool

Instantly transpose spectacle cylinder sign (+ to - cylinder) and calculate Spherical Equivalent (SE) for contact lens and intraocular lens (IOL) selection.

Original Rx InputsSpectacle Rx (Diopters)
Input Format:Minus (-) Cylinder
Vertex Distance (mm):12 mm
Optical Calculations Output
Spherical Equivalent (SE)
-3.12D

SE = -2.50 + (-1.25 / 2)

Transposed Rx (+ Cyl Form)
-3.75 +1.25 × 90°
Medsy Eyecare EMR

Medsy includes built-in optical refractions, contact lens inventory management, and auto-transposition for eyecare clinics.

Explore Medsy Eyecare Modules →

The 3 Rules of Prescription Transposition

  1. New Sphere: Algebraically add Sphere + Cylinder.
  2. New Cylinder: Change the sign of the Cylinder value (+ to - or - to +).
  3. New Axis: Add or subtract 90° to the original axis (keep within 1° to 180°).

When to use Spherical Equivalent (SE)

SE is widely used when fitting spherical soft contact lenses, evaluating refractive surgery candidates, prescribing preliminary glasses, or calculating IOL power when low astigmatism does not warrant a toric lens.