OD stands for "oculus dexter" which is Latin for "right eye". The right eye is always listed first on the prescription.

OS stands for "oculus sinister" which is Latin. We'll give you free shipping if you can guess its English translation. It's always listed second on a prescription.

Sometimes abbreviated to PWR, SPH, or something similar, they all mean the same thing: it's the strength of your prescription.

It will have a plus or minus before it depending on if you're nearsighted (-) or farsighted (+).

It's a number between 8 and 10 that measures the curve of the lens. The larger the number, the flatter the lens. The base curve determines how the lens fits on your eye and most brands only produce contacts in a couple of base curve options.

The width of the lens in millimeters. Most brands manufacture contacts in one standard size between 13.5 and 15 mm wide.

This is for people with an astigmatism. This is when one part of the eye needs more correction than the rest of the eye. Cylinder is different than your Power measurement and is written with a minus (-) sign.

The axis measurement is only for people with an astigmatism. The axis is a number between 0 and 180 and determines the orientation of the cylinder within the lens.

The brand is part of the prescription and specifies which kind of contacts you can buy. Each brand is made with a specific material and water content.

If you wear colored contacts, you can order any color that’s available within the brand you were prescribed.

Your prescription is valid for one or two years, depending on which state you live in.