How to Read Your Contact Lens Prescription
Here is a typical contact lens prescription:
Here are the definitions of the symbols used:
- OD - Right Eye
- OS - Left Eye
- OU - Both Eyes
- BC - Base Curve
- Dia - Diameter
Toric (Astigmatism correcting) lenses will also contain two
Bifocal contact lenses generally contain one additional number which is the add power. A special field will be given for this number.
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- A contact lens prescription is not the same as an eyeglass
prescription. In addition to the lens power, your contact lens
prescription contains several other pieces of information related to
the size of the lens.
- Your prescription will also contain an expiration date. This is
typically two years from the date that the contact lenses were
- BC values range from about 8.0 to 9.5. The doctor fits the lens
with the curvature most appropriate for your eye. Most lenses come
in several different BC values. If your prescription does not
contain a BC value, this is likely because your brand of lens only
comes in one base curve.
- BC values are a bit like clothes sizes - just because you are a BC
8.6 in one brand doesn't mean you will be in another.
- If you are in a toric lens your prescription will contain two
additional columns entitled cylinder and axis. These numbers related
to the correction of your astigmatism.
- Even the power of the lenses is generally not the same as in your
eyeglass prescription. This is because:
- The contact lens sits on the surface of your eye, while your
eyeglasses sit about 12 mm in front of your eye
- Regular soft contacts do not correct for your astigmatism, but
your eye doctor will typically try to partially correct for it
by changing the power of the lens.
Reading Your Contact Lens Prescription