Understanding your contact lens prescription
Your contact lens prescription contains specific information to ensure your contact lenses are safe, comfortable and provide optimum vision.
If you're in the U.S., your contact lens prescription is yours to keep. In fact, by law your eye care practitioner must give you a copy of your prescription at the conclusion of your contact lens exam and fitting — even if you don't ask for it. If you don't have a contact lens prescription, schedule an appointment with an eye doctor near you.
Eye doctors use standard terms, abbreviations and measurements to write contact lens prescriptions. It may look like a secret code, but it's really quite simple to decipher.
Below is an example of a contact lens prescription. Place your cursor over each term or number, and it will be explained on the right:
In addition to the above information, if you wear disposable contact lenses, your prescription may include how often your contact lenses should be replaced (once a month, every two weeks, once a week, daily, etc).
Sometimes the lens brand includes information about the recommended replacement schedule (e.g., Ophtha-Lens One-Week), but the real judge is your eye care practitioner, who knows what's best for your eyes and lifestyle.
It's also important to note that contacts and eyeglass prescriptions are not the same. So even if you already have an eyeglass prescription, you will need a separate contact lens prescription before you can purchase contacts.
Can You Buy Contact Lenses Without A Prescription?
No, under U.S. law the purchase of all contact lenses requires a valid contact lens prescription written by a qualified eye care practitioner.
Your eye care practitioner can only write your contact lens prescription after a thorough contact lens exam and fitting.
Why Do You Need A Prescription?
It is illegal to sell contact lenses without a prescription, and for good reason.
Even if you buy your replacement contacts from another source, you still need to visit your eye doctor for regular eye exams and contact lens fittings.
A contact lens is a medical device, and a poorly fitted lens — or one made from a material not well-suited to your eyes — can cause distorted vision, discomfort, infection, inflammation, swelling and abrasion. In rare cases, permanent eye tissue damage could result.
And it goes without saying that you should never share your contact lenses, including colored contacts and theatrical contacts. Sharing contact lenses can cause potentially sight-threatening eye problems.
When Does Your Prescription Expire?
By law, contact lens prescriptions are valid for a minimum of one year, or the minimum required by state law, whichever is greater.
When your prescription expires, you won't be able to buy more lenses until your eye care practitioner gives you an updated prescription. This will involve an eye exam to check your general eye health and to be certain that contact lenses aren't adversely affecting your eyes.
"Just because your eyes feel good and your contact lenses seem to be working well does not mean your eye health is O.K.," says Charles Slonim, MD, an ophthalmologist in Tampa. "You may be having microscopic problems that can be seen only with a slit lamp [a type of microscope used during an eye exam]."
Dr. Slonim says that about 10 percent of the time when he sees a patient during a follow-up visit, he notices something that could become a problem if not taken care of immediately.
If you are diagnosed with a contact lens-related problem, it's unlikely that you'll have to discontinue wearing contacts permanently. In most cases, a change to a different type of lens or different contact lens solution — or a modification of how often you replace your contacts — will solve the problem.
Where Can You Use Your Contact Lens Prescription?
Once you've been properly fitted by your eye doctor and have a valid contact lens prescription, you have the option of buying contact lenses from a wide variety of sources.
These include your eye care practitioner, optical chains, warehouse clubs, mass merchandisers and online retailers.
Wherever you choose to purchase your contact lenses, always make sure you buy your contacts from a legitimate source. Vendors selling contact lenses without a prescription, such as you might find in a flea market, gas station or novelty shop, are breaking the law.
Aimee Rodrigues also contributed to this article.
Page updated September 2016