Provide a valuable resource to your clients or customers by linking to this resource page. Just place the following link on your website.
The mathematical method used to convert a spherocylinder lens prescription (used to correct astigmatism) from the plus cylinder notation to the minus cylinder notation, or vice-versa, without changing the optical power of the lens.
read more about transposition ...1. Algebraically add the sphere and cylinder powers to find the new sphere. 2. Change the sign of the cylinder power. 3. Change the axis by $90^\circ$ (add $90^\circ$ if the original axis is $90^\circ$ or less; subtract $90^\circ$ if the original axis is over $90^\circ$).
A prescription of $+2.00$ Sphere $ ext{ / }-1.00$ Cylinder $ ext{ X } 180^\circ$ transposes to $+1.00$ Sphere $ ext{ / }+1.00$ Cylinder $ ext{ X } 90^\circ$. Both prescriptions are optically identical.
While the patient sees the same, transposition is crucial because many ophthalmic instruments and lens grinding systems standardize on either the plus or minus cylinder format.
No. Transposition ensures the net optical effect and the power in every meridian remain exactly the same.
Changing the sign of the cylinder power means the meridian of maximum or minimum power shifts by $90^\circ$, requiring the axis notation to also shift by $90^\circ$ to describe the same lens.
Ophthalmologists and optometrists often use plus cylinder notation during subjective refraction, while opticians typically fill prescriptions using minus cylinder notation.