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How to Read Your Glasses Prescription

Here’s a quick rundown of how to read your eyeglasses prescription, so that you can safely create a weaker glasses prescription to support your vision training.

I recommended you downgrade from a pair of full strength glasses now to decrease the near point stress on your eyes. It will also encourage your eyes to work harder and focus properly without an overpowering prescription. For more information on this, see How to Safely Obtain Weaker Glasses.

Making Sense of Your Eyeglass Prescription

Your prescription may appear to be written in mysterious code but actually once you understand the meaning of the symbols, it will all make sense.


Right Eye and Left Eye Abbreviations

OD – This stands for oculus dexter which is the Latin term for right eye. Not so mysterious now, eh?

OS – This is another Latin word, oculus sinister, this one meaning left eye.

OU – Your prescription may or may not contain this one. It stands for oculus uterque which means both eyes.

Note: Some optometrists have updated their prescriptions and done away with these Latin abbreviations. Instead you might see RE (right eye) and LE (left eye).

Lens Powers

Sphere (SPH) – This shows the strength of your glasses, or lens power, measured in diopters (D). A negative (-) sign indicates nearsightedness (in which case you have myopia) while a positive (+) sign or no sign at all indicates farsightedness (hyperopia).

Cylinder (CYL) – This shows the lens power for astigmatism, the condition of having an irregular lens shape caused by both nearsightedness and farsightedness. It is measured in plus and minus diopters as above. If the Cylinder field is empty, you have no astigmatism so there is no correction needed.

Axis – This is a number from 1 to 180 which describes the lens meridian that contains no cylinder power to correct astigmatism. If your eyeglass prescription has a Cylinder power, it must also have an Axis value (sometimes preceded by an x when written in freehand).

Add – This field contains any added magnifying power for people with presbyopia (or aging vision) and is featured in the bottom part of a multifocal lens. As a result, this is always a positive (+) number and is usually the same in both eyes.

Prism – This is for the uncommon occurrence of eye alignment problems. It is measured in Prism Diopters (p.d. or a superscript triangle if written freehand).

Base – This refers to the thickest edge of the Prism, which is also the direction towards which the Prism redirects light (up, down, in, or out).

What To Do With Your Glasses Prescription

When your eye exam is finished, your optometrist is legally obligated to give you a copy of your new glasses prescription. That’s so you have the choice to either purchase eye glasses from them, or take your prescription to another vendor.

This is very valuable if you are doing vision training. First it means you don’t have to buy an expensive pair of glasses from your optometrist (there are so many stores that sell overpriced frames, it is easy to feel ripped off after a visit).

Second, it means that if your optometrist doesn’t support vision training (only about 1 in 10 have the qualifications in this area) then you can still get a weaker prescription elsewhere. I recommend buying glasses online at a good quality supplier like 39 Dollar Glasses so you can save money as you go through multiple pairs of increasingly weaker glasses.

For more advice on creating a weaker prescription to support your natural vision improvement, see my article on Improving Your Vision with Weaker Glasses.

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