A typical contact lens prescription:

Below are the definitions of the symbols/abbreviations used in a typical contact lens prescription:

• Eye - Which eyes the prescription line item is for.
  • OS - Left Eye
  • OD - Right Eye
  • OU - Both Eyes
• BC - Base Curve (usually a number between 8 and 10)
• DIA - Diameter (usually a number between 13 and 15)
• SPH - Sphere (referred to as Power or PWR can be a negative or positive number)
• Brand - The brand name or type of contact lens that your Eye Care Provider has fitted you for.

Toric (Astigmatism correcting) Prescriptions

Astigmatism is blurred vision and is caused by an eye that is not completely round. Certain patients require contact lenses that are manufactured for toric or astigmatism correction. Prescriptions for these types of lenses contain two additional numbers that relate to the correction of the astigmatism. These two numbers are usually separated by an "X" and are indicated with the following symbols/abbreviations.

• CYL - Cylinder (usually a number between -4.00 and +4.00)
• AX - Axis (usually a number between 0 and 180)

Bifocal or Multifocal Prescriptions

Some patients require lenses that are bifocal or multifocal. Prescriptions for these types of lenses will contain an additional number with the following symbol/abbreviation.

• ADD - Also known as "Add Power" or "Extra Strength"

Additional Rx Information

• 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.
• 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 10-12 mm in front of your eyes
  • 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 will also contain an expiration date. This is typically one to two years from the date that the contact lenses were fitted.
• Base Curve values range from about 8.0 to 10.0. The doctor fits the lens with the curvature most appropriate for your eye. Most lenses come in several different Base Curve values. If your prescription does not contain a Base Curve value, this is likely because your brand of lens only comes in one base curve.
  • Base Curve values are a bit like clothes sizes - just because you are a Base Curve 8.6 in one brand doesn't mean you will be the same in another brand.
• Though not common, sometimes you can have a regular prescription for one eye, and a toric or bifocal prescription for your other eye. In this case you will not only have different parameters for each eye, but also usually a different brand/type of lens as well.

Instructions

Take note of the information presented in a prescription, including: power, base curve, diameter and brand name or type of contact lens your Eye Care Provider has fitted you in. Bifocals and astigmatism prescriptions typically have additional information.

Learn the abbreviations used in a prescription:

• OS - for left eye
• OD - for right eye
• BC - for base curve
• PWR - for Power
• DIA - for Diameter

Look for additional abbreviations used for bifocals:

• ADD - for additional power

and astigmatism/toric:

• CYL - for cylinder
• AXIS - for astigmatism

Locate the prescription on the side of the box as seen below:

Read the measurement of the diameter (DIA), given in millimeters; this is the distance from one edge of the contact lens to the other.

Read the power (PWR) of the lens strength (it may be different for each eye), measured in diopters. The higher the power number, the stronger the prescription is. Look for a minus sign to indicate nearsightedness (myopia) and a plus sign that indicates farsightedness (hyperopia).

Read the base curve (BC) measurement in millimeters. The lower the number, the steeper the cornea of a patient's eye. If this measurement is not included, it is likely that the brand has only one standard base curve value.

Locate the brand name or type of contact lens your Eye Care Provider has fitted you in.