Deciphering Your Eyeglass Prescription

eyeglass prescription

When you order glasses online, you will be asked to fill out your eye prescription. But what exactly do these numbers and letters mean? At Optical Plus, we believe in educating our customers and have provided a breakdown of what your eyeglass prescription actually means.

OD/OS/OU: These are short for oculus dexter (OD), oculus sinister (OS) and oculus uterque (OU). These are the Latin terms for the right eye (OD), left eye (OS) and both eyes (OU). These distinctions are especially useful when your eyes have two different prescriptions. If your left eye and right eye have different prescriptions, it’s very important to know which is which.

Sphere (SPH): Sphere is the number directly beside each eye. While each number on your prescription is important, this is the one that denotes the lens power or strength of your prescription, whether you are near or far sighted. If your SPH has a negative symbol that means you are nearsighted. If your SPH has a positive symbol or no symbol at all, it means you are farsighted.

Cylinder (CYL): Cylinder is the lens power that’s included in your prescription if you have astigmatism. Sometimes, nothing can appear in this column, which means you do not have astigmatism in need of correction. When there is a number, it will also be classified into near and farsightedness by a plus (far) or a negative (near).

Axis: The axis is measured on a scale of 1-180. It is used when your prescription also has a Cylinder and it describes the lens meridian used to correct astigmatism. It can often have an “X” written before it.

Add: This is used for multifocal lenses. It is a number that will always be a positive strength, representing the magnifying power to correct presbyopia. The magnifying power is only applied to the bottom of the glasses.

Prism: Prism is used to correct eye alignment problems. You will see 5 different abbreviations representing the following: prism diopters (p.d.), base up (BU), base down (BD), base in (BI) and base out (BO). The measurement for your correction will be denoted in a decimal or fraction in p.d. and the base directions are used to show the direction.

You’ll need all of the above information from your eyeglass prescription in addition to your Pupillary Distance (PD) to order glasses online from Optical Plus.

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