Rx Transposition

Convert minus-cylinder to plus-cylinder form; axis rotates 90°.

Medical Disclaimer

This calculator is for informational and educational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider before making decisions about your health. Never disregard professional medical advice or delay seeking it because of results from this tool.

Inputs

Sphere (D)

Cylinder (D)

Axis (°)

Tab to move between fields

Results

Sph (−cyl)

-2.5

Cyl (−cyl)-0.75

Sph (+cyl)-3.25

Cyl (+cyl)0.75

New axis90

How to Use This Calculator

Locate your eyeglass prescription from your optometrist.
Enter the sphere (SPH), cylinder (CYL), and axis values for each eye.
Read the converted notation in the output panel.
Compare the output with your lens order form to verify accuracy.
Consult your eye-care professional before ordering lenses.

How the result changes with Sphere (D)

Sphere (D)	Sph (−cyl)
-24	-24
-9	-9
9	9
24	24

What each input means

Sphere (D): The spherical power from your prescription in minus-cylinder form. Negative values correct nearsightedness.
Cylinder (D): The cylinder power for astigmatism correction. In minus-cylinder form, this is typically negative.
Axis (°): The cylinder axis in degrees (1-180). During transposition, the axis rotates by 90 degrees.

What each result means

Sph (−cyl): Sphere value in minus-cylinder notation (your original input).
Cyl (−cyl): Cylinder value in minus-cylinder notation.
Sph (+cyl): Sphere value after transposing to plus-cylinder notation.
Cyl (+cyl): Cylinder value in plus-cylinder notation (sign is flipped).
New axis: The transposed axis after rotating 90 degrees.

How this is calculated

Worked example, using the default values

Identify Input Parameters
Sphere (D) = -2.5, Cylinder (D) = -0.75, Axis (°) = 180 = 3 input(s) provided
Calculate Sph
Sph = sph
-2.5 = -2.5
Calculate Cyl
Cyl = cyl
-0.75 = -0.75
Calculate Sph
Sph = round((sph + cyl) * 100) / 100
-3.25 = -3.25

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