An eyeglass prescription describes the optical correction required for each eye. The abbreviations look complex, but each has a defined role. It is not the same as a contact lens prescription and does not include every measurement needed to make glasses.
The main terms
OD / OS
Right eye and left eye.
SPH
Spherical power: minus usually for myopia, plus for hyperopia.
CYL
Cylinder power used to correct astigmatism.
AXIS
Orientation of the cylinder from 0° to 180°.
ADD
Additional near power for reading or multifocal lenses.
PD
Pupillary distance used when centring lenses.
A simple example
SPH −2.00 indicates spherical correction for myopia. If CYL −0.75 and AXIS 90° are also present, the prescription includes astigmatism correction at that orientation. Values should not be interpreted in isolation or changed without a new examination.
Why are more measurements needed?
Making the glasses may require PD, fitting height and the actual position of the frame. With progressive and specialist lenses, accurate fitting is critical to the useful viewing zones.
Need help understanding your prescription?
Bring the prescription and chosen frame for appropriate lens selection and centration.
