Several abbreviations can appear on one prescription line, but they are not interchangeable numbers. SPH, CYL/AXIS, ADD and PRISM describe different optical components that must be read together.
01 · SPH
SPH is spherical power acting in all meridians
SPH means sphere. Plus and minus values indicate opposite directions of spherical correction and are recorded in diopters.
SPH alone does not describe the whole prescription when cylinder or prism is present.
02 · CYL & AXIS
CYL and AXIS work together to describe astigmatic correction
CYL is the power difference between principal meridians, while AXIS gives the orientation of the zero-cylinder meridian. If CYL is zero, axis has no optical role; with larger CYL, orientation becomes more consequential.
Plus- and minus-cylinder forms can be transposed, so compare prescriptions in the same convention.
03 · ADD
ADD is extra plus power used mainly for near work
Addition is the near-power increment used with a distance prescription in progressive, bifocal or near designs. The same ADD can behave differently depending on working distance and lens design.
Read ADD in relation to the distance prescription rather than as a standalone complete prescription.
04 · PRISM
PRISM changes image position relationships and requires a base direction
Prism is commonly written in prism diopters together with BI, BO, BU, BD or a base angle. A magnitude without direction is incomplete.
Prescribed prism should be distinguished from induced prism created by looking away from a lens optical center.
05 · FABRICATION DATA
The prescription is not the entire set of manufacturing data
Fabrication may also require monocular PD, fitting height and the frame trace. Personalized designs can additionally use vertex distance, pantoscopic tilt and face-form angle.
Autorefraction results, old-lens lensmeter readings and the final prescription are different kinds of data and should not be treated as the same record.
SOLUTION GUIDE
A practical check order
Read SPH, CYL/AXIS, ADD and PRISM by their distinct roles.
Confirm OD/OS or R/L before comparing values.
Identify cylinder convention and prism-base notation.
Use PD, fitting height and frame information for fabrication.
GLANOS CHECK
A prescription provides optical powers, while finished eyewear also depends on centration, frame and processing data.
Interpret each abbreviation first, then consider how the components interact in the finished lens.
CAUTION
Do not equate an autorefraction printout with the final spectacle prescription.
The final prescription follows the examination and clinical decision, while fabrication requires additional fitting measurements.
GLANOS EYEWEAR
There is usually a reason behind eyewear discomfort.
SPH · CYL · AXIS · ADD · PRISM · eyeglass prescription