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Thursday, October 22, 2015

How To Read A Prescription

How do you Read Your Contact Lens Prescription?
Good question. 
Here is your typical contact lens prescription...

Eye Power
BC Dia Brand
OD (Right) -2.25 8.8 14.0 Acuvue
OS (Left) -3.00 8.8 14.0 Acuvue

and... 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 have two additional numbers as well:
  • Axis  
  • Cyl - Cylinder
How about Bifocal contacts?

Bifocal contact lenses will typically contain 1 additional number which is the add power. There will be a special field for this number.

Please keep the following information in mind:

  1. A contact lens prescription is not going to be the same as an eyeglass prescription. The lens power is different and, in addition to this, your contact lens prescription contains several other pieces of information related to the size of the lens. 
  2. Your contact lens prescription will also contain an expiration date. Typically this will be 2 years from the date that the contact lenses were fitted.
  3. BC values range from about 8.0 to 9.5. The doctor will fit the lens with the curvature most appropriate for your eye. Most lenses will 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 only.
  4. BC values are a bit like clothes sizes ---- just because you are a BC 8.4 in one brand doesn't mean you will be in another.
  5. If you are in a Toric lens your prescription will contain 2 additional columns entitled cylinder and axis. These numbers related to the correction of your astigmatism.
  6. Also, the power of the lenses is typically not the same as in your eyeglass prescription. This is for the following reasons:
    1. The contact lens sits on the surface of your eye, while your eyeglasses sit about 12 mm in front of your eyes.
    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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