What it means and why
SPH is the spherical component of a prescription, expressed in dioptres (D). Read the sign before the number: minus and plus have different optical effects. With a cylinder present, the spherical value is only one part of the complete description, not the whole lens.
Keep the right and left rows separate. A change in SPH should be interpreted alongside CYL, AXIS, vision and the examination conditions; comparing the largest printed numbers alone can be misleading.
A worked example
Teaching example: SPH −2.00 D and +2.00 D have equal numerical magnitude but opposite signs. Neither can replace the other. If CYL −1.00 D is also written, retain it and its axis; reporting only “two dioptres” would lose essential information.
What it does not tell you
SPH is not visual acuity. It cannot tell you how many chart letters the person sees or establish that the eyes are healthy. Do not turn a glasses prescription into a contact-lens order by copying SPH alone.
THINK IT THROUGHWhat is missing from “my power is two”?
At least the sign, eye, units and the other prescribed components. Read the complete right and left rows.
Sources & reading notes
Page updated:
- AOP · Your prescription explained ↗ Professional body guidance
Explains terminology and dispensing practice; it is not a head-to-head product trial.