Looking to transpose your eyeglass prescription? Transposing an Rx is a fairly simple process that involves converting one set of spherical measurements into another. This can be useful if you are looking to order new glasses online, or simply want to understand how your current prescription works. Learn how to transpose an eyeglass prescription here at Optical Academy!
There are several steps involved in transposing an Rx. The first is to convert the vertical and horizontal distances from the original prescription into diopters. This can be done using a simple mathematical formula, which takes into account the minus and plus values of each number in your prescription. Learn how to read your prescription in our blog post: How To Read Your Eye Prescription
Once you have converted your vertical and horizontal measurements into diopters, you will need to convert them back into the same unit. This process involves taking the Cylinder value from your prescription and converting it into diopters using a similar formula.
Once you have your new diopter values, you can use a transposition chart to convert them into new measurements. Simply enter your numbers into the corresponding fields on the chart and it will output your new prescription information. From there, you can easily order your glasses or contacts online using this information. Go to this transposition calculator to calculate the transpose of your RX.
3 Steps to Transpose Your Prescription
Step 1: Add the sphere and cylinder components together
|New Sphere||= original sphere + original cylinder|
|= +2.50 + (-1.50)|
|= +2.50 – 1.50|
Step 2: Change Cylinder Sign
If the cylinder sign is +, change it to -. Vice Versa if it starts with -.
|New Cylinder||= the same absolute value of the original cylinder but the opposite sign|
|= – (original cylinder)|
|= – (-1.50)|
Step 3: Change the axis by 90 degrees
Add or remove 90 degrees to the axis depending on the original axis. If the original axis is less than or equal to 90 degrees then add 90. When 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|
|Original Rx||+2.50 -1.50 x 20|
|Transposed Rx||+1.00 +1.50 x 110|