How is a Contact Lens Number Different From a Glasses Prescription?

If you wear contact lenses, or are thinking about switching from glasses to contacts, you may notice that your contact lens prescription looks different than the one you have for eyeglasses. This is because your contact lens prescription includes extra abbreviations and numbers that don’t appear on glasses prescriptions, as well as specific information about how the lenses should fit your eyes.

The most obvious difference between a contact lens prescription and a glasses prescription is that the contact lens prescription will include abbreviations for your eyes, as well as numbers that correspond to them. You will see OD (oculus) and OS(oculus sinister), abbreviations for your eyes, along with a numerical value that represents the strength of the correction. The number will either be a plus (+), or minus (-),, depending on whether or not you are farsighted or nearsighted.

CYL is often included in your contact lens prescription. This is shorthand for cylinder. It refers to how much astigmatism you may have. If you have astigmatism, your prescription will require a contact lens with a cylinder correction in addition to the spherical correction required for normal vision.

You may also see the abbreviation OU in your contact lens prescription. This stands for “unilateral.” It means that you suffer from monocular astigmatism. This is when you have astigmatism on both sides of your eyes, but not as much in one as the other. Your doctor will usually recommend that you wear contact lenses with a CYL correction if you have monocular astigmatism, as this will make your prescription easier to manage and read.

Lastly, your contact lens prescription may also include a value for base curve, which is another factor that your glasses prescription doesn’t usually have. This value is important for contact lenses, because it refers to how the curve of your cornea matches the shape of the contact lens you’re wearing. This is essential for ensuring your lens fits properly. It also determines how comfortable and transparent your contact lenses are.

While there are some websites that claim to be able to convert your glasses prescription to a contact lens prescription, these tools are not always accurate. In many cases, results will be inaccurate due to extra specifications included in a prescription for contact lenses. Only by visiting your eye doctor for a fitting and contact lens examination can you get a complete and accurate conversion.

Please don’t hesitate if you have any questions regarding the reading of your contact lens prescription. Our friendly team of experts will be happy to help. You can reach us at 888-576-3937. We look forward to hearing from you!