OD Eye vs. OS Eye: How To Read Your Contact Lens Prescription (Updated)

When you take a comprehensive eye exam, an eye care professional (ECP) will assess the health of your eyes and check for any eye conditions. Your ECP will also assess your vision and, if necessary, give you a prescription for contact lenses.

A typical contact lens prescription contains many abbreviations and numbers, which is why it can look incredibly complex to the uninitiated. But don’t fret. The truth is reading a contact lens prescription isn’t that hard once you know what those abbreviations and numbers mean.

Lens.com is here to help you do just that. In this article, we break down the parts of a typical contact lens prescription so that you can better understand yours.

What do the abbreviations on my contact lens prescription mean?

Profile of a contact lens box showing DIA, axis, and other information.

A typical contact lens prescription will include the following abbreviations:

  • OD – This stands for Oculus Dexter, which is Latin for “right eye”. All the values listed alongside OD pertain to your right eye.
  • OS – This stands for Oculus Sinister, which is Latin for “left eye”. All the values listed alongside OS pertain to your left eye.
  • OU – This stands for Oculus Uterque, which is Latin for “both eyes”. If there are values listed alongside OU, that means both of your eyes have the same prescription.
  • PWR or SPH – PWR stands for “power” and SPH stands for “sphere”. The value listed under PWR or SPH is the refractive power (measured in diopters) that the eye will need to be able to see in 20/20 vision. The higher the PWR or SPH value, the stronger the vision correction you need. Some contact lens prescriptions might contain PWR, while some may contain SPH. PWR or SPH may also appear as “D,” which stands for “diopter.”
  • Negative PWR (- PWR) – A negative value under PWR on your contact lens prescription means you have myopia (nearsightedness).
  • Positive PWR (+ PWR) – A positive value under PWR on your contact lens prescription means you have hyperopia (farsightedness).
  • BC – This stands for “base curve”, which is the curvature of your cornea measured in millimeters. BC is important because its value determines how well the contact lens fits your eye. Having an incorrect value listed under BC will mean that the contact lens doesn’t fit your eye well.
  • DIA – This stands for “diameter”, which is the width of the contact lens from edge to edge measured in millimeters. DIA determines the width of the contact lens that best fits your cornea.
  • BRAND – This refers to the brand of contact lenses that your ECP recommends for you. In case you have a bad experience with a specific contact lens brand, consult your ECP about using a different brand.

If you’ve been prescribed toric lenses for astigmatism or multifocal lenses for presbyopia, your prescription will contain these additional abbreviations:

  • CYL – This stands for “cylinder”. A negative CYL value indicates myopic astigmatism while a positive CYL value indicates hyperopic astigmatism.
  • AX – This stands for “axis.” It refers to the direction where another power is added to the contact lens to correct astigmatism. Axis is measured in degrees.
  • ADD – This stands for “additional power.” It refers to the magnifying power added to multifocal lenses to correct presbyopia and help with close-up tasks (e.g., reading). The value listed under ADD is always positive (+). It may also appear as “high,” “medium,” or “low.”

If you’ve been prescribed colored contact lenses, your prescription will also contain “COLOR.” This simply refers to the color of the contact lenses prescribed to you. Even if you don’t need vision correction, your ECP will recommend a brand of contact lenses and note that on your prescription.

Note that your prescription will also include an expiration date. Once it expires, make an appointment with your ECP to obtain an updated one or use our online vision exam at Lens.com to easily renew your prescription from the comfort of your home.

What do the numbers on my contact lens prescription mean?

Most of the abbreviations on a contact lens prescription are followed by numbers. Here’s what those numbers mean:

  • Positive (+) number – If a number has a plus sign before it, that means you’re farsighted.
  • Negative (-) number – If a number has a minus sign before it, that means you’re nearsighted.

For example, take a prescription with a PWR value of -2.25. This means you need 2.25 diopters of strength to correct nearsightedness. If that value were +2.25, that means you would need 2.25 diopters of strength to correct farsightedness.


Just because your prescription is hard to read doesn’t mean it’s impossible to understand. With this article as your reference, you’ll be able to understand any contact lens prescription moving forward.

Note that your contact lens prescription isn’t a one-and-done thing. Your vision may change over time, so it’s important to see your ECP regularly.

FAQs About Contact Lens Prescriptions

  • What if my prescription is expired?

You can use our fast and convenient online vision exam to renew your prescription. The exam itself takes about 10 minutes, and a board-certified ophthalmologist will review your results within 24 hours. Once approved, you’ll get a copy of your renewed prescription.

  • Do I need a copy of my prescription to order contact lenses from Lens.com?

No, you don’t need to send us a copy of your prescription to order contact lenses from us. You can send it to us if you want to as it will help us ship your order faster, but it’s not required. You only need to provide us with your ECP’s name and contact information, and we’ll verify your prescription for you.

For your information, federal law requires your ECP to give you a copy of your prescription whether or not you ask for it. Moreover, ECPs may not condition the release of your prescription on your agreement to buy contact lenses from them. They also can’t charge you an extra fee to release your prescription.

  • Do I have to order the brand on my prescription?

Yes, the brand is part of the prescription, so you have to order what your ECP prescribed. Different contact lens brands are made with different base curves and diameters, which is why your ECP chooses one for you during a contact lens fitting.

As a replacement center, we can only sell you contact lenses that you are already using. Consult with your ECP if you’d like to change the brand of contact lens that you’re wearing.

  • Can I use my eyeglasses prescription to order contact lenses?

No, you can’t and shouldn’t use your eyeglasses prescription to order contact lenses because a prescription for eyeglasses isn’t the same as a prescription for contact lenses. Eyeglasses sit slightly away from the eyes, while contact lenses sit directly over the eyes. Therefore, the parameters specified on your eyeglasses prescription may be significantly different from those on your contact lenses prescription.

It’s also worth noting that not everyone who wears eyeglasses can also wear contact lenses. If you’re already wearing eyeglasses and you want to switch to contact lenses, schedule a visit with your ECP.

  • Can I get colored contact lenses without a prescription?

No, colored contact lenses are still considered medical devices even if they have zero power, so they must be properly fitted and prescribed by an ECP. Consult with your ECP if you want to try colored contact lenses.

Already have a prescription? Shop Lens.com today and enjoy hassle-free returns, quick shipping, and a 100% money-back satisfaction guarantee. We stock several popular brands from leading contact lens manufacturers, including Johnson & Johnson, Bausch + Lomb, and Alcon.