What is the minus cylinder form of -2.50 +1.00 x 175?

To determine the minus cylinder form of a prescription such as -2.50 +1.00 x 175, it is essential to understand what minus cylinder form entails. In minus cylinder notation, you express the spherical component with the cylinder component showing a negative power.

In this case, starting with the prescription, you have a sphere of -2.50 diopters and a cylinder of +1.00 diopters at an axis of 175 degrees. To convert this to minus cylinder form, it's necessary to adjust the cylinder power and simultaneously adjust the spherical power.

When transforming a prescription into minus cylinder form, one generally subtracts the cylinder from the sphere and changes the sign of the cylinder. Thus, if you take the original sphere of -2.50 and the cylinder of +1.00, you get:

• Sphere: -2.50 - 1.00 = -1.50

• Cylinder: -1.00 (as the sign is changed)

The axis also needs to be adjusted. The original axis of 175 degrees, when adjusting for a -1.00 cylinder, shifts to 85 degrees (which is 90 degrees minus the original axis of 175 degrees).

So the resulting prescription in minus cylinder form