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
additional numbers:

• Cyl – Cylinder
• Axis 

Bifocal contact lenses generally contain one additional number which is the add power. A special field will be given for this number.

Notes

1. 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. 

2. Your prescription will also contain an expiration date. This is
   typically two years from the date that the contact lenses were
   fitted.

3. 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.

4. 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.
5. 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.

6. Even the power of the lenses is generally not the same as in your
   eyeglass prescription. This is because:
   1. The contact lens sits on the surface of your eye, while your
      eyeglasses sit about 12 mm in front of your eye

   2. 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.