Deciphering Your Contact Lens Prescription

contact lense

You have been to the Ophthalmologist and have your contact lens prescription in your hand, expect the fact that the prescription makes no sense to you. Don’t worry; you are not the only one who cannot understand the contact lens prescription. It is not the doctor’s handwriting that’s unclear; instead, it is the numbers and abbreviations that mean nothing to you.

When you are ordering contact lenses, whether from contactlenses-4 US or from any other online source, you need to provide accurate details so that your lenses fit appropriately and allow you to see clearly.

Contact lenses are a medical device that has specific instructions for comfortable wear, and despite the fact you don’t have to know what the codes and abbreviations mean, you may be curious.

This is a quick guide to decipher your contact lens prescription.

Reading my contact lens prescription

  • Power/Sphere (PWR/SPH): it is the measurement stating how farsighted or nearsighted you are and how much improvement your eyes require. Power/Sphere is measured in ‘Diopters,’ which measures the lens’ curve.
  • Plus (+) Sign before a number in the PWR box indicates that you are farsighted (longsighted). Farsightedness means you see better far away than up close. The higher the number, the more longsighted you are.
  • Minus (-) Sign before a number in the PWR box indicates that you are nearsighted (shortsighted). Nearsightedness means you see better up close than far away. The higher the number, the more shortsighted you are.


  • Diameter (DIA): Diameter of a contact lens determines the width that best fits your eyes. It is measured in millimeters and range typically between 13-15 mm. If the number is incorrect, the lens’ edge will not place correctly on your eye, causing abrasions and irritation.


  • Base Curve (BC): The base curve indicates the nature of fit needed for the lens to meet the curvature of your cornea. It is measured in millimeters and sometimes used with the terms – steep, median, or flat.


  • OS and OD: OS and OD are short for Oculus Sinister and Oculus Dexter. In some cases, OU is written on the contact lens prescription. OU is short for Oculus Utreque.
  • OS denotes the Left Eye
  • OD denotes the Right Eye
  • OU denotes Each Eye (the measurement will be the same for both the eyes)


  • Brand: The Brand section denotes the brand recommended by your Ophthalmologist for your eyes based on your requirements and prescription.

People who have Astigmatism will see more codes and abbreviations in their contact lens prescription. They include:

  • AXIS: Axis denotes the number in degrees (0-180) that identifies the astigmatism correction position.
  • CYL: CYL refers to Cylinder, which is a number (in minus) that increases in measure of 0.25. CYL represents the additional visual requirements essential for Astigmatism. It also denotes how severe your Astigmatism is.
  • ADD: ADD refers to Addition, which determines the level of correction required for you to see clearly at a closer range. This is included in the prescription of the patient suffering from ‘Presbyopia.’

Lastly, if you wear bifocals, a non-dominant and dominant eye determines your lens correction. The non-dominant eye is identified with an N, while the dominant eye is identified with a D.

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