What is the correct transposition of the plus-cylinder prescription +1.00+2.00x90 to its minus-cylinder?

To transpose a plus-cylinder prescription to its equivalent minus-cylinder form, it's essential to understand the method of transposing cylindrical prescriptions.

In a plus-cylinder prescription, such as +1.00 +2.00 x 90, the first number (+1.00) represents the sphere component, the second number (+2.00) represents the cylinder component, and the axis (x 90) indicates the orientation of the cylinder. When transposing this prescription to minus-cylinder:

1. The sphere and cylinder components are adjusted. The sphere power is increased by the cylinder power, while the cylinder power becomes negative.

2. The axis also shifts 90 degrees from its original position. Since the original axis is at 90 degrees, adding 90 degrees to it results in 180 degrees.

So, taking the original prescription +1.00 +2.00 x 90, you add the cylinder value of +2.00 to the sphere value of +1.00, yielding +3.00. The cylinder value then becomes -2.00, and the axis changes from 90 degrees to 180 degrees. Therefore, the transposed minus-cylinder prescription would be +3.00 -2.00 x 180.

This corresponds to