Contact Lens Prescriptions Explained

It may seem like gibberish but those numbers and abbreviations on your contact lens prescription are important. When ordering contact lenses online, you’ll need to have your prescription handy to ensure you’re getting the right lenses. Not only will the correct contact lens prescription enable you to see clearly, it will also mean the lenses you order actually fit your eyes for optimal comfort and safety. Confused by the jargon? Have no fear. Fresh Lens is here with our guide to understanding your contact lens prescription.

Breaking Down Your Contact Lens Rx

Most contact lens prescriptions contain the following abbreviations:

• OD, OS and OU: OD is the right eye and OS is the left eye. OU means each eye and might be used if the measurement is the same for both peepers.

• SPH (or Power or PWR): The sphere or power is the measure of nearsightedness or farsightedness and tells the amount of correction needed in diopters. If there is a minus sign before the number, you’re nearsighted. A plus sign would mean you’re farsighted. The larger the number, the more correction needed.

• BC: BC stands for base curve and is typically a number between 8 and 10. This refers to the curvature of the lens, which should complement the curvature of your cornea for comfort.

• DIA: DIA or diameter is a number between 13 and 15 and is a measurement in millimeters of the lens width. This number is super important because the edge of the lens needs to rest in the correct place for comfort and to avoid irritation or abrasions.

• Brand: This indicates the brand the optometrist fitted you for.

If you have astigmatism, your prescription will also contain the following:

• Axis: The axis is shown in degrees between 0 and 180 and indicates the position of the astigmatism correction.

• CYL: CYL stands for cylinder and measures the degree of correction needed for your astigmatism.

If you need bifocal or multifocal lens your prescription will note:

• ADD – This means “add power” or “extra strength” and indicates the additional strength you’ll need to see up close.

Your prescription may also note the color of the lenses if you’re going for fancy colored contacts as well as an expiration date, which is usually one to two years after the fitting.

Can I Buy Contact Lenses Without a Prescription?

While it may seem convenient to forgo the trip to the eye doctor to get a prescription, it’s ill advised. By law, to purchase contact lenses in the U.S. you need a valid prescription from an eye care practitioner (either an optometrist of ophthalmologist). Why? Because contact lenses are considered medical devices and if they don’t fit right or aren’t made from approved materials, you won’t be able to see clearly and you run the risk of infection, abrasions or in rare cases, permanent damage to the eyes. When people buy contact lenses in Canada or the U.S. from Fresh Lens, we require a valid prescription. You can be rest assured your vision will be on point, the lenses will fit and your eyes will be comfortable.

What is a Contact Lens Fitting?

So now that we’ve explained the ins and outs of your contact lens prescription, are you ready to go get your eyes examined so you can order a batch of contacts online? Well, it’s important to note that the eye exam for contact lenses includes a few extra steps and your eyeglasses and contact lens prescriptions are different. So when you see your ophthalmologist or optometrist be sure to indicate you want a contact lens fitting as well.

After you navigate your way through the usual, “Which one is clearer? A or B?” and stare down that eye chart, the eye care professional will measure your cornea using an instrument called a keratometer and might break out the corneal topographer for an even more precise evaluation. The size of the pupil and iris may be measured too. They’ll then take a look at the surface of your eye and check out the contact lens’s fit with a trial pair and a biomicroscope. Once they’ve nailed down which contact lenses will work best for you, you’ll be given your prescription. Then you’ll be ready to take advantage of the ease of ordering contact lenses online in the U.S. and Canada, at Fresh Lens, of course.

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