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You just finished your annual eye exam and with prescription in hand, you're thinking about what kind of cool eyeglasses to try. Have you ever looked at all those numbers and letters and wondered what exactly do they mean? Whether you’re a longtime glasses wearer or a newbie, knowing how to decipher your prescription will give you a better understanding of what the eyeglass prescription could say about your vision and overall health.


Trying to read a prescription for glasses isn’t the easiest thing in the world, so we whipped up this guide to help you understand better what do the numbers in your eyeglasses prescription mean.

The key to reading your eyeglasses prescription, whether you have nearsightedness, farsightedness, astigmatism or anything else, is knowing what OD and OS stand for.

  • O.D. stands for oculus dexter, meaning the right eye.
  • O.S. stands for oculus sinister, meaning left eye.

There are other abbreviations in your eye prescription. 
These abbreviations reflect the measurements of specific aspects of your vision and can be pretty confusing at first.

  • SPH (or Sphere) indicates the eyeglass prescription power, or how strong your lenses need to be to correct your vision.
  • CYL (or Cylinder) indicates astigmatism, a condition where the cornea is irregularly shaped causing blurred or distorted vision. It also tells the lens strength needed to fix it.
  • AXIS describes the degree and direction of your astigmatism.
  • ADD is added magnifying power in the lower part of a multi-focal lens. It’s used to correct presbyopia which is the inability to focus on close objects. If you need a bifocal or progressive lens, there will be an ADD.

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Your glasses prescription includes a number for every aspect of your vision that needs correction. When learning how to interpret your prescription, keep in mind that usually the further from zero the numbers are, the more correction you need.

A plus or minus sign in front of your glasses’ prescription number is shorthand for near or farsightedness.

+ means you’re farsighted or have trouble seeing things close up.
– means you’re nearsighted or struggle with seeing far away.

How often should you get an eye exam?

If you don’t have any medical issues that affect your vision, you should have a comprehensive eye exam every one to two years.

Children should have their first eye exam when they are around six months old, and then another just before they start school. This ensures that they can see clearly in class; poor vision can seriously impact a child’s learning

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