# Transpose an Rx

Transposing an Rx is one of the many lens calculation utilities included in VirtualLens 3D. It is easy enough to transpose an Rx manually, but if you don't feel like thinking about it and you don't happen to have the latest version of VirtualLens 3D fired up, then you can use this free online utility. To see a short refresher about manually transposing an Rx, see below.

# Free Online Transpose Rx Calculator

Enter the Rx and click the buttons to convert the Rx to plus or minus cylinder form. Javascript must be enabled in your browser for this calculator to work.

# How to Transpose an Rx in VirtualLens 3D:

In the Lens Properties dialog, where the current Rx is, click the Calculators button and select Transpose Rx, then select one of the transpose options to convert to plus or minus cylinder form. This will convert the current Rx.

# How to manually Transpose an Rx:

Transposing an Rx refers only to prescriptions where there is a cylindrical component, spherical prescriptions cannot be transposed. There are three steps to tranposing, one for each component of the Rx; sphere, cylinder, and axis. The following Rx will be used in these steps for clarity:

Original Rx | +2.50 -1.50 x 20 |

# 1) Add the sphere and cylinder components together algebraically:

New Sphere | = original sphere + original cylinder |

= +2.50 + (-1.50) | |

= +2.50 - 1.50 | |

Answer | = +1.00 |

# 2) Change the sign of the cylinder:

New Cylinder | = the same value of the original cylinder but the opposite sign |

= (-1) * original cylinder | |

= (-1) * (-1.50) | |

Answer | = +1.50 |

# 3) Change the axis by 90 degrees:

Either add 90 degrees or subtract 90 degrees. Use the one that gives an answer in the range of 1-180 degrees.

New Axis | = the original axis + or - 90 |

= 20 + 90 = 110 Yes | |

= 20 - 90 = -70 No | |

Answer | = 110 |

# The new transposed Rx, which is exactly the same as the original Rx, is:

Transposed Rx | +1.00 +1.50 x 110 |

Original Rx | +2.50 -1.50 x 20 |