Compute transposition, spherical equivalent, and induced prism (Prentice's Rule).
Enter the current prescription to calculate the transposed Rx and spherical equivalent.
Apply Prentice's Rule to calculate the induced prism.
Opticians, optometrists, and optical students use an optical lens transposition calculator to convert prescriptions between plus-cylinder and minus-cylinder form, estimate spherical equivalent, and apply Prentice prism checks. It reduces arithmetic errors when interpreting refractions, ordering lenses, teaching optics, or verifying how decentration can create unwanted prism.
Add the cylinder power to the sphere, change the cylinder sign, and rotate the axis by 90 degrees while keeping it within the 1 to 180 degree axis range.
No. Plus-cylinder and minus-cylinder forms describe the same refractive correction when transposed correctly. The notation changes, not the lens power relationship.
Spherical equivalent is the sphere plus half the cylinder. It is useful for summaries, contact lens discussions, or screening, but it does not replace the full astigmatic prescription.
Prentice's Rule uses prism diopters equal to decentration in centimeters times lens power in diopters. Direction depends on lens sign and the direction of decentration.