How to read an Eye Prescription


The idea of reading an eyeglasses prescription may sound about as appealing as bathing with snakes, but isn’t it important to know all the facts when it comes to your health? That little piece of paper you absentmindedly take from the optician actually holds the key to knowing exactly what is wrong with your eyes. Plus you can use the information to save a lot of money by buying your prescription glasses and sunglasses online, perhaps at VisionDirect.

The numbers on your prescription are usually measured in diopters, D, and the further from zero the numbers are, the worse your eyesight is. It’s important to have regular check-ups to make sure that if your eyesight changes, then you can change your lenses accordingly. Adults should have an eye exam once every two years and children once a year (sorry for sounding like your mum, but this stuff’s important).

Eye Prescription Explained

Prescription Blank copy

Eyeglasses Prescriptions have many abbreviations and differing terms. We’ve listed below some of the most common items that will appear on a prescription.

OD – The first line of your prescription is always for your right eye. Referred to as OD, this is just Latin for right eye (because it wan’t already complicated enough). Can also be written as R.

OS – The second line of your prescription is for your left eye. Referred to as OS, you guessed it, this is Latin for left eye. Can also be written as L.

Axis – This number, expressed in degrees, refers to the direction of the astigmatism.

ADD – The ADD or additional value, expressed in D, is present for people who need reading glasses, bifocal or multi-focal glasses. It indicates the power added to your Sphere value for reading or close up work. If there is only one ADD power, it means you need the same ADD for both eyes.

Prism/Base – This shows how the glasses will compensate for eye alignment problems. If the number is present, it will be written with; BU, BD, BI or BO. This indicates which direction it is from the base.

Pupillary Distance (PD) – This is the distance between your pupils, measured in mm. A single PD value is measured between the centers of the pupils of the right and left eye. Sometimes, you may be given a dual PD value; Right eye PD and Left eye PD. This is the distance from the center of pupil of each eye to the center of the bridge. This information is essential when fitting prescription lenses, if not written down, be sure to ask your optometrist for the measurement.

Buy Prescription Glasses Online

Congratulations if you managed to get through all that. If you’ve still got questions, feel free to leave a comment and we’ll get back to you. In the mean time, why not use your new found knowledge to save that money we talked about? We have a great selection of designer glasses and sunglasses and we can even fit your prescription for you. Happy hunting eye wear genii.


  1. I’ve seen optometrists throughout my life, but I never understood how to read the prescription. It’s good to know that OD is for my right eye and OS is for my left eye. The next time I see an optometrist for new lenses, I will be able to read my prescription. Thanks!

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