Learn how to transpose an eyewear prescription easily inside by learning a few simple rules!
For those just coming into the world of optics, prescriptions can be confusing. However, learning to read them and work with them is easier than what comes to the naked eye. Transposing a prescription is one of the most common actions when working in an optical laboratory, doctor’s office or even on a retail floor when an optician. Some eye doctors prescribe eyeglasses in what is called plus cylinder, and others do so in minus cylinder. Regardless of which is used, the prescriptions are the same. This can be proven by transposing the eyewear prescription.
For instance, if one takes an eyewear prescription with OD -2.75 -1.00 x 25, one can transpose this rather simply with a few steps in mind.
First, the sphere power needs to be changed by adding the second number or cylinder power to it. The result will be as follows: OD -3.75 -1.00 x 25.
Next. the second number, or cylinder power, will always have a sign change when transposed. Therefore, the second change from in the original eyewear prescription will be OD -3.75 +1.00 x 25.
Finally, and one of the most important steps is to add 90 degrees to the axis, which is the last number in the prescription. This gives you a totally transposed prescription that looks like the following:
-3.75 +1.00 x 115
Both the -2.75 -1.00 x 25 and -3.75 +1.00 x 115 are the same prescription(Rx), and they appear totally different! It is just that simple.
Optical laboratories tend to work in minus cylinder as this is the way the lenses are ground for the final product, therefore, it is vital for not only lab technicians to know but crucial for an Optician.