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Your Eyeglasses Prescription - What Does it Really Mean?


Have you ever really know what your optical prescription (Rx) means? Many people have been wearing eyeglasses since early in life and have little to no idea. How do you know which is for the right eye versus the left eye? Why does your prescription have one set of numbers, but your friend's has three? The answers to these questions and more are easily explained.

In the example below, let's start with the terms "OD" and "OS". These are abbreviations taken from the latin words oculus dextrus, meaning "right eye", and oculus sinister, meaning "left eye". Optometrists and ophthalmologists have used these terms within the optical community for years. You may see another term, "OU", which means oculus utro and refers to an Rx or condition involving both eyes.

Sample prescription from Clarkson EyecareNow on to the numbers themselves. A good rule of thumb when reading a prescription is this: the further from zero each number is, the worse your eyesight. This could mean a number of things, from needing higher quality eyeglass lenses to requiring toric contact lenses for an astigmatism.

The first number represents the diopter, which is the unit measuring the correction needed for the eye to properly focus. A plus sign means you're farsighted, or hyperopic. A minus sign means you are nearsighted, or myopic. If there are three numbers in your prescription you have an astigmatism, or an irregularly shaped cornea requiring further vision correction. The second and third numbers in the line refer to the "cylinder", or astigmatism itself, and the "axis", the orientation of the astigmatism on the cornea.

The sample prescription above has four numbers total, because this is for a bifocal or progressive lens prescription. The final number corrects for presbyopia, a condition that typically develops in the early 40s requiring an Rx for reading up close.



Hi , 
Your post really helped me to understand optical prescription. It has great details and yet it is easy to understand. 
That's what i was looking for. I will definitely share it with others. 
Thanks for sharing.
Posted @ Tuesday, March 04, 2014 5:21 AM by Prescription Eyeglasses
It is very can do something that most people can not.Your article can inspire someone to do such as something.It will be beneficial for many people.Thank you.
Posted @ Wednesday, March 19, 2014 1:15 AM by Prescription Reading Glasses
Great blog post. It’s useful information. What to do when we havva buy Reading Glasses Online?
Posted @ Wednesday, March 19, 2014 6:28 AM by Kim
Oh i really never knew about what optical prescription (Rx) means. This is a really good site post, im delighted I came across it.
Posted @ Monday, May 26, 2014 1:17 AM by RX Eyeglasses
Yes agree with your post that we must have an idea about eyeglasses and specially Prescription Eyeglasses before wearing eyeglasses...true that many people don't know more about it...
Posted @ Monday, May 26, 2014 1:45 AM by Joseph
Do i need to get a prescription for my reading glasses after a cataract operation?
Posted @ Wednesday, July 30, 2014 6:47 AM by eye care dubai
excellent & useful article. Thanks. If you could tell what does cylinder power related to this it would be more useful. Thanks again.
Posted @ Thursday, August 28, 2014 3:01 AM by Vanessa Bire
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