Determining Your Prescription

• 1). Obtain a copy of your contact lens prescription from your eye doctor. By law, he must provide you with a written prescription after you have had a complete contact lens exam and final fitting, which may involve more than one appointment.
  
  
• 2). Locate your right and left eye on the written prescription. These are usually noted as O.D. (Latin for ocular dexter) for the right eye and O.S. (ocular sinister) for the left eye or O.U. (ocular utrique) for both eyes. They may also be marked simply as "Right Eye" and "Left Eye."
  
  
• 3). Find the power of the lens, which may be noted as Power or PWR. This number is also referred to as a Diopter and is the refractive power of the lens, calculated by your eye doctor to bring your vision to as close to 20/20 (perfect vision) as possible.
  
  
• 4). Note whether the power is written with a minus or plus sign before the diopter number. These numbers range from minor correction starting at zero and can go to 20 diopters or higher, in increments of 0.25. Minus power is for myopia, or nearsightedness, and plus power is for hyperopia, or farsightedess.
  
  
• 5). Look for numbers written as, or under a column labeled, CYL or Cylinder. If this is indicated on your prescription your contact lenses also correct for astigmatism. This number is also written in diopters and will also include another number under AXIS, the location of the cylinder between zero and 180 degrees.
  
  
• 6). Disregard B.C. (Base Curve), C.T. (Center Thickness) or DIA (Diameter) on your prescription when trying to determine the strength of your contact lenses as these numbers are needed only for the size and fit of the lens, not the strength.