RefraCard
How to read a contact lens prescription
A contact lens prescription looks like a glasses prescription with extra columns. The extra columns are the ones that decide whether the lens fits, and they are not interchangeable between brands.
Field by field
The corrective power in dioptres, minus for short-sight and plus for long-sight. Not the same number as your glasses if the prescription is strong — see why the two differ.
The back curvature in millimetres, typically 8.3 to 9.0. Matched to your cornea during the fitting. A brand may only offer one or two base curves.
The lens width in millimetres, usually 13.8 to 14.5.
Astigmatism correction. Available in coarser steps than spectacles, so the values are often rounded to the nearest lens the brand makes.
Frequently expressed as LOW / MED / HIGH rather than a dioptre value, because each manufacturer designs its own near zones.
Daily, two-weekly or monthly. Part of the prescription — the fitting was done in that specific lens.
Expiry
Contact lens prescriptions typically run shorter than spectacle ones — often a year — because the fit and the health of the eye surface need re-checking, not just the vision. An aftercare appointment is what renews it.
Both eyes, always
Lenses are ordered per eye, and the two are frequently different in more than power — base curve can differ too. When you record a contact lens prescription, record it per eye in full; a single line of numbers is not enough to reorder from.