How to transpose an eyeglass prescription easily !

Learn how to transpose an eyeglass prescription easily by learning a few simple rules!

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.

Transpose a prescription written in plus cylinder form to minus cylinder form as follows:

1. Add the sphere and cylinder powers to determine the new sphere power.
2. Change the sign of the cylinder.
3. Change the axis by 90 degrees.

Example 1:

Transpose -3.00 +2.00 x 30
Step 1	Add the sphere and cylinder powers to determine the new sphere power.	(-3.00) + (+2.00) = -1.00
Step 2	Change the sign of the cylinder	-2.00
Step 3	Change the axis by 90 degrees. (if the axis is 90 or less than 90, add 90 degrees to the axis, if the axis is greater than 90 deduct 90 from the axis)	120
The transposed prescription is: -1.00 -2.00 x 120

Example 2:

Transpose -3.00 -2.00 x 30
Step 1	Add the sphere and cylinder powers to determine the new sphere power.	(-3.00) + (-2.00) = -5.00
Step 2	Change the sign of the cylinder	+2.00
Step 3	Change the axis by 90 degrees. (if the axis is 90 or less than 90, add 90 degrees to the axis, if the axis is greater than 90 deduct 90 from the axis)	120
The transposed prescription is: -5.00 +2.00 x 120

Example 3:

Transpose +3.00 -2.00 x 30
Step 1	Add the sphere and cylinder powers to determine the new sphere power.	(+3.00) + (-2.00) = +1.00
Step 2	Change the sign of the cylinder	+2.00
Step 3	Change the axis by 90 degrees. (if the axis is 90 or less than 90, add 90 degrees to the axis, if the axis is greater than 90 deduct 90 from the axis)	120
The transposed prescription is: +1.00 +2.00 x 120

Example 4:

Transpose +3.00 +2.00 x 30
Step 1	Add the sphere and cylinder powers to determine the new sphere power.	(+3.00) + (+2.00) = +5.00
Step 2	Change the sign of the cylinder	-2.00
Step 3	Change the axis by 90 degrees. (if the axis is 90 or less than 90, add 90 degrees to the axis, if the axis is greater than 90 deduct 90 from the axis)	120
The transposed prescription is: +5.00 -2.00 x 120

credit: opticianworld, ehow, laramyk