What does my prescription mean?
A prescription reads like code: −3.75 / −1.25 × 170. Type yours in below and get every number translated into plain English.
Right eye: -3.75 / -1.25 × 170°
-3.75 SPH - short-sighted (myopia)
Strong. Anything past your elbow is already a smear.
Without correction, the world stays sharp out to about 27cm and blurs beyond it.
-1.25 CYL × 170° - astigmatism
Moderate astigmatism - lights grow tails, text doubles faintly.
The axis tells the lens which orientation the correction sits at - here, along the 170° line. A toric lens has different power in different directions to cancel the uneven curve of your cornea.
Left eye: -4.00 / -0.75 × 10°
-4.00 SPH - short-sighted (myopia)
Strong. Anything past your elbow is already a smear.
Without correction, the world stays sharp out to about 25cm and blurs beyond it.
-0.75 CYL × 10° - astigmatism
Mild astigmatism - edges smear slightly along one angle.
The axis tells the lens which orientation the correction sits at - here, along the 10° line. A toric lens has different power in different directions to cancel the uneven curve of your cornea.
The contact lens extras
A contact lens prescription carries a few numbers a glasses one doesn't, because the lens has to physically fit your eye.
BC - Base Curve
How steeply the back of a contact lens curves, in millimetres. It's matched to the shape of your cornea so the lens sits centred and stable - a typical value is 8.4–8.8.
DIA - Diameter
The overall width of the lens in millimetres, usually around 14. Together with base curve it decides how the lens fits - which is why contact lens and glasses prescriptions aren't interchangeable.
PWR / SPH - Power
The focusing strength of the lens in dioptres. Contact lens power can differ slightly from your glasses SPH because the lens sits on the eye rather than 12mm in front of it.
ADD - Addition
Extra plus power for reading, used in multifocal lenses once presbyopia arrives (usually from your mid-40s). Often written as LOW / MED / HIGH rather than a number.
Now that you know what the numbers mean…
See what your prescription actually looks like on a street, a menu or the night sky.
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