RefraCard
What does SPH mean on your prescription?
SPH — sphere — is the headline number of your prescription: the main focusing power of the lens, measured in diopters (D). Everything else on the paper is a refinement of it.
THE ANATOMY OF A PRESCRIPTION
| SPH | CYL | AXIS | ADD | |
|---|---|---|---|---|
| OD | −2.25 | −0.75 | 175 | +0.75 |
| OS | −2.75 | −0.50 | 12 | +0.75 |
Minus means short-sighted, plus means long-sighted
The sign is the important part, and it is not a grade — it is a direction.
- A minus number (−2.25) corrects short-sightedness — myopia. Your eye focuses light slightly in front of the retina, so distance is blurry while close work stays naturally sharp. The lens moves the focus back.
- A plus number (+1.50) corrects long-sightedness — hyperopia. Your eye under-powers close focus. Young eyes compensate by working harder, which is why hyperopia often shows up first as tired eyes or headaches rather than blur.
- Plano, 0.00 or an em dash means no spherical correction is needed in that eye — any correction there is astigmatism only.
How strong is strong?
There is no official cut-off, but optometry generally reads myopia in these bands — and the same magnitudes apply, mirrored, on the plus side:
Mild. You likely see well enough to move around a room unaided; distance detail — signs, faces, a whiteboard — is what you lose.
Moderate. Glasses or lenses become the default rather than an aid for specific tasks.
High myopia. Worth tracking carefully: it carries a raised long-term risk of retinal problems, which is exactly the sort of thing a decade of prescriptions makes visible.
SPH is not the same in both eyes — and that is normal
Almost nobody has two identical eyes. A difference of a diopter or more between them has a name — anisometropia — and matters mainly because it can affect how comfortably the two images fuse. What is worth watching is not the difference itself but whether it is growing, which only a history can tell you.