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Reading your Contact Lens Prescription

Understanding your contact lens prescription might feel overwhelming, especially if you're new to wearing contact lenses. In this blog, we’ll guide you through the basics of reading contact lens prescriptions.



One of the first steps to understanding your contact prescription is knowing the common abbreviations and terminology that come with them. Often, people need specific prescriptions for each eye, so you may see different abbreviations according to the lens. Below are the most common abbreviations/terms that you will most likely see on every prescription:


  • OD: Oculus dexter, or your right eye

  • OS: Oculus sinister, or your left eye

  • SPH/PWR: The sphere number on your prescription will be between -20 and +15. These two abbreviations stand for sphere and power and are often used interchangeably. Sphere and Power describe the strength of your prescription. A positive number indicates farsightedness, while negative numbers indicate nearsightedness.

  • CYL: Cylinder measures the amount of astigmatism, if present, in your eyes. This value will be listed as zero if you do not have astigmatism. 

  • DIA: The diameter value accounts for the full width of your contact lens. This number often falls in the range of 14-14.5. 

  • BC: The base curve value is always between 8 and 9. Why is this important? The base curve of your lens is important because it should align well with the curvature of your eye. 

  • AXIS: The axis value corresponds to the orientation of the astigmatism in your eye. This value is represented in degrees and always falls between 0 and 180. 

  • ADD: This stands for addition or additional magnification. This value represents the additional power required for your vision. ADD is often listed in terms such as “Add Power” or “Extra Strength.” 

  • D/N: This stands for dominant or non-dominant eye. Sometimes, lenses have different levels of correction, so it is important to be able to differentiate the two. 



A prescription is typically valid for one to two years but can vary. Contact lens websites should not accept prescriptions that are expired. Follow up with your eye care professional regularly to ensure your prescription remains up-to-date! 

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