- How to read your prescription
- Contact lens prescription checklist
When considering purchasing contact lenses online, the first step is a visit to an optometrist or an ophthalmologist. Here’s what to expect.
Before the Exam
Generally, a visit to the eye doctor includes an eye exam, a fitting, and a prescription. When you intend to use your prescription to shop elsewhere, there are a few questions and concerns you should address in advance. Before your exam, ask the doctor if they will prescribe a national brand. Some doctors will only prescribe private label lenses that are not available anywhere but from them.
Contact lens prescriptions are brand specific and cannot be substituted. National brands are available to be purchased anywhere, so requesting this in advance will make it easier to fill your prescription later. Doctors are legally required to provide a written copy of your prescription upon request. Be sure to ask for a copy each time you have an eye exam.
Once you have established that your doctor will prescribe a well-known brand, you will need an eye exam and a contact lens fitting. Contacts come in a variety of sizes, and the doctor will need to measure your eyes to get the right fit. The size will also depend on the type of lenses you want. The most common are soft lenses and RGP,or Rigid Gas Permeable lenses (read our RGP article here). Your doctor should go over your lens options with you and help you determine which will best meet your needs. If you already wear contacts, but would like to try a different brand, it is best to have a new eye exam so you can be fitted for that brand.
Contact lenses are prescription medical devices. Even if you just want to purchase cosmetic contact lenses that change your eye color, you will still need an eye exam and a prescription from an eye doctor. The same applies to costume or theatrical contact lenses. However, you may not need a vision test to get a prescription for this type of lens – ask your eye care provider about their policy.
Can I Use My Eyeglass Prescription?
Contact lens and eyeglass prescriptions are quite different. Again, a contact lens must match the size and shape of your eye. Therefore, a prescription for contact lenses contains information like base curve and diameter, as well as brand. Also, glasses rest about 12 millimeters from your eyes, while contacts sit directly on the eye. Contact lenses made to conform to an eyeglass prescription would be stronger than necessary, which could cause vision problems. Finally, your glasses are shaped to correct for astigmatism (irregular curve in the cornea or lens). However, contacts must be designed to fit the astigmatism, if there is one. If you have a prescription for glasses and would like to try contacts, visit your eye doctor for a new exam and contact lens fitting. Don’t forget to mention you will need a copy of your prescription.
A typical contact lens prescription looks like this:
|1. Eye||2. Brand||3. BC||4. DIA||5. SPH/PWR||6. CYL||7. AXIS||8. ADD||9. Color|
|OD (Right)||Acuvue Oasys for Astigmatism||8.8||14.0||-2.25||-1.25||160||Blue|
|OS (Left)||Acuvue Oasys for Astigmatism||8.8||14.0||-3.00||-1.75||180||Blue|
- Eye – Refers to which eye the prescription line item is for. The OD (oculus dexter) means Right Eye, while OS (oculus sinister) refers to Left Eye.
- Brand – The specific brand or type of contact lens that your eye doctor has fitted you for.
- BC – This stands for Base Curve, and is the diopter measurement, in millimeters, of the inside curve of your contact lenses. It is usually a number between 8 and 10 and is sized to match or correct the curvature of your eye.
- DIA – Short for Diameter, this measurement refers to the size, in millimeters, from edge to edge of the contact lens. Soft contact lenses are larger than RGP lenses, but either way, the diameter usually falls between 13 and 15.
- SPH – Also referred to as Power or PWR, this field references the corrective factor of the contact lenses. A negative number, such as -2.25, in this field indicates myopia, (nearsightedness), while a positive number like +2.25 indicates hyperopia (farsightedness). If your prescription shows the letters PL, which stands for Plano, it means the no correction is needed.
- CYL – This measurement, which stands for Cylinder, shows how much astigmatism, if any, you have. It is measured in diopters.
- AX – Short for Axis. Measured in degrees, the axis references the placement of the power in the lens, to compensate for the cornea’s shape when there is astigmatism.
- ADD – Used for bifocal contact lenses, the number here, measured in diopters, adds a degree of magnification to certain portions of the lens.
- Color – The customer’s requested tint, if any.
Your prescription will also have an expiration date, usually one to two years from the date of the day it was given to you. Note that once your prescription has expired, you can no longer use it to buy contacts.
Contact Lens Prescription Rights
You are legally entitled to a copy of your contact lens prescription, even if you forget to ask for one at the time of your visit. You may request a copy at any time after the prescription has been finalized. Make sure that the prescription is good for at least one year after the date it was requested – that’s the minimum, not the maximum, required by law. You do not have to sign a waiver or pay a fee to get your contact lens prescription. If your eye care provider tries to insist that you to do either of these, refuse; these practices are illegal. You are also not obligated to purchase your lenses from the outlet where your prescription was issued. You have the right to get your prescription filled whenever and wherever you choose.
Now that you’ve had your exam and fitting and have been given your prescription, double check to make sure everything is in order.
- Make sure that you have been given a prescription for contact lenses and not for eyeglasses. A prescription for disposable contact lenses will always include a contact lens brand name.
- Also, verify that the prescription is filled out completely and accurately, with all the relevant information. A soft lens prescription usually includes a lens material name, design, power, base curve, and diameter. RGP prescriptions may also include peripheral curve radii, center thickness, a special peripheral design and an optical zone diameter.
- Once you’ve verified that all the information is correct, you are ready to make a contact lens purchase from the outlet of your choice.