Transposing an Rx refers only to prescriptions where there is a cylindrical component. Spherical prescriptions (no cylinder and no axis) cannot be transposed. There are three steps to transposing an Rx and each eye must be transposed individually.

Example:

 Original Rx +2.50 -1.50 x 20

The example Rx above is in 'minus cylinder form' and can be converted to 'plus cylinder form' by following the 3 steps below.

NOTE: It does not matter if you are converting the cylinder from minus to plus or from plus to minus, the exact same steps are followed.

#### 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:

If the cylinder is + change it to -, if the cylinder is - change it to +

 New Cylinder = the same absolute value of the original cylinder but the opposite sign = - (original cylinder) = - (-1.50) Answer = +1.50

#### 3) Change the axis by 90 degrees:

Either add 90 degrees to the axis or subtract 90 degrees from the axis. Use the result that is in the range between 1 and 180 degrees.

• If the original axis is less than or equal to 90 degrees then add 90
• if the original axis is greater than 90 degrees then subtract 90.
 New Axis = the original axis + or - 90 = 20 + 90 = 110     YES = 20 - 90 = -70     NO Answer = 110

#### The new Transposed Rx, which is identical to the Original Rx:

 Original Rx +2.50 -1.50 x 20 Transposed Rx +1.00 +1.50 x 110