Saturday, November 24, 2007

How to Read Your Contact Lens Prescription

Here is a typical contact lens prescription:

OD (Right)-2.258.814.0Acuvue
OS (Left)-3.008.814.0Acuvue

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.

  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.

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