Optical Calculators

Transposition Calculator

Convert a prescription between plus cylinder and minus cylinder form. Enter the sphere, cylinder and axis, and the calculator applies the standard transposition formula without changing the optical power.

Any prescription with cylinder can be written two ways that mean exactly the same thing. Ophthalmologists usually write plus cylinder, while optometrists and most lab surfacing equipment use minus cylinder. Transposing switches between the two.

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The calculator does three steps:

  1. Add the sphere and cylinder to get the new sphere.
  2. Change the sign of the cylinder.
  3. Rotate the axis 90°: add 90 if the axis is 90 or less, subtract 90 if it's more.

Use it whenever an Rx needs to match a different format for your lab or software.

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