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
Here are some facts you should remember:
1. A contact lens prescription is not the same as an eyeglass prescription. Your contact lens prescription contains several pieces of information related to the size of the lens.
2. The prescription should also contain an expiration date. Typically it lasts for two years since the date that the contact lenses were fitted.
3. Base curve values range from about 8.0 to 9.5. The eyecare practitioner fits the lens with the curvature most appropriate for your eye. The majority of lenses come in several different BC values. If there is no BC value in your prescription, this is likely because your brand of lens only comes in one base curve.
4. Base curve 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 were prescribed to wear toric lens, the prescription itself should contain two additional columns entitled cylinder and axis. These values are related to the correction of your astigmatism.
6. The power of the lenses is generally not the same as in your eyeglass prescription, because the contact lens sits on the surface of your eye, while your eyeglasses sit about 12 mm in front of your eye; and 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.
Your prescription may note how often your contact lenses must be replaced (once a month, every two weeks, once a week, daily, etc.), or you may be instructed verbally, during your exam.
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