Understanding Your Glasses Prescription


When you get a new pair of glasses, the first thing you should notice is an improvement in your vision. This is because your unique prescription has been added to the lenses allowing you to see better.

Before you get your new glasses made, your optometrist will provide you with all the details of your prescription. These numbers may seem a bit strange, but each one helps create a pair of lenses that fit your specific vision and lifestyle needs.

Your Glasses Prescription Explained

You may have tried on a friend’s or family member’s glasses and found that you do not have the same vision needs. That’s because we each have our unique prescription designed to help improve the way we see the world. If you order prescription glasses online, it’s important to understand these numbers so that you can make sure you are getting the right pair for your vision.

Before ordering a pair of glasses online, you should make sure that your prescription is up to date. This will ensure the pair of glasses you get are clear and accurate. There are several factors that would prompt the need for a new prescription:

  • The current prescription has expired
  • A change in vision such as blurred vision while wearing your current glasses
  • You want to switch from contact lenses to glasses
  • Your lenses are damaged or scratched

Your eye doctor will do a complete eye exam to check to see if any adjustments in your prescription are required. They will then provide you with an updated prescription for a new pair of glasses. It will also indicate whether you require single vision, progressive or bifocal lenses.

How to Find Out What Prescription Your Glasses Are

Your prescription is specific to your vision needs. Whether you are near-sighted, farsighted, or have astigmatism, your prescription is customized to accommodate your vision correction needs.

Your eye doctor will use several tests to determine what prescription will best improve your vision, including using equipment like the phoropter to get an accurate prescription reading. They will also take special measurements to ensure that your glasses are centered properly on your face for the best vision possible.

Once your eye doctor has all the calculations, they will calculate your prescription.

If you look at your new prescription you will see several boxes with numbers in them such as +1.50 or -2.00. Each of these numbers corresponds with a particular part of your prescription specifications.


Though it may seem strange, OS and OD determine which eye the prescription is for. OD means right eye and OS means left eye. OU means both eyes.

ADD and Distance

The ADD and the distance help explain the kind of vision that you have. Minus means you are nearsighted, while plus means you are farsighted. For example, a prescription that is -1.50 means you are nearsighted. A prescription that is +2.50 means you are farsighted.

The ADD lets the lens maker know how much magnification you require. The higher the prescription, the more magnification is needed to help you see clearly.


The amount of cylinder power required changes depending on the level of astigmatism. This number is usually a minus such as -3.50. The cylinder helps bring objects into focus and helps the eyes work together to create a perfect image.


The sphere indicates the amount of lens power required to help you see better. As noted earlier, these can be plus or minus numbers that help determine how much assistance you need to see clearly. If you are having a lot of difficulties seeing, then this number can be quite high such as a +6.50 or -4.00.

PD Measurement

The pupillary distance or PD measurement is the distance between the pupils of your eyes. This helps your eye doctor determine where your line of sight falls to ensure your glasses are aligned properly. It is measured between the center of your pupils to get the most accurate reading.

Seg Height

The seg height measurement is important when fitting bifocals. This measurement is taken from the bottom of the lens of your frames to the point where the progressive addition begins.


The axis determines the angle between the meridians of the eye with astigmatism. This number falls between 1 and 180.

How to Order Prescription Glasses Online

Now that you have a better idea of what the information on your prescription means, you can enter the information online with confidence. Simply select the kind of lenses you require based on your eye doctor’s suggestion after choosing a pair of stylish frames from our wide range. Then, upload your prescription and place your order so our team can begin making your glasses. If your eye doctor hasn’t provided you with your PD, we have a simple and useful tool once you choose your lenses to help you measure this yourself.

Right now, Specs for Vets customers can enjoy 25% off all frames when using the promo code FRAMES25 or discounted sunglasses using the code SUN25 at checkout.

Have a question about your order? Give us a call at 888-501-5011 or contact us here.

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