Contact lens prescription is the first document you need to have before you can order contact lenses. The prescription is both medical and legal document for buying contact lenses.
Just like medicines, contact lenses are a prescription item. If they aren’t properly prescribed, besides you can’t see well, they could result in discomfort, or even eye infection.
However, it’s also a legal matter because your eye doctor is required by the law to give a copy of the prescription to you at the end of lens fitting. Or, if you buy lenses from suppliers other than your doctor, they aren’t allowed to deliver your lenses before verifying the lens prescription to your eye doctor.
Contact Lens Prescription and Prescription Expiration
The minimum elements of a lens prescription include your name, your doctor name and the lens brand and material. It also contains power, cylinder, axis, diameter, base curve, peripheral curves, color, and add information.
A more detailed prescription will include wearing schedule, allowed material substitutions, and an expiration date. Each item is abbreviated to fit to a prescription form.
If you’ve been wearing eyeglasses you might notice a glasses prescription. But a prescription for contact lens contains additional lens information, such as brand, diameter, base curve and possibly additional curves lens material. Here the power of contact lens is different as that of a glasses prescription because a contact lens is closer to the eye.
The U.S. law allows eye doctors to set prescription expiration dates. It is usually valid for a minimum of one year, or the minimum required by state law, whichever is greater.
An eye doctor may set an earlier than one year expiration date only if he or she has a medical judgment for your eye health. The doctor must document the detail medical reason for shorter expiration date so that it can be reviewed by a qualified medical professional.
When your prescription expires, you aren’t allowed to buy lenses until you get a new, updated prescription. This will involve a follow up eye examination to make sure that contact lenses aren’t adversely affecting your eyes.
Reading Your Contacts Prescription
Eye doctors use abbreviations and numbers on your contact lens prescription. Here’s a guide to decipher common terms used in your contact lens prescription:
- OD — right eye
- OS — left eye
- Power (pwr) — the strength of correction, in diopters, your lenses must provide for an acceptable distance vision correction (-20 to +20). A diopter is a unit of measurement that helps determines how much a lens should be altered to bend light rays to achieve correct focus. Farsightedness is designated by a plus sign and nearsightedness by a negative sign.
- Base Curve (BC) — Base curve describes the curvature of contact lens’ back surface, measured in millimeter. For best fit, it’s prescribed to match the curvature of your cornea.
- Diameter (diam) — size of the contact lens, measured from edge to edge. This info is useful to determine where on the eye the lens edges will rest.
- Add power (add) — expressed in diopters, it is used to show additional power for close-up viewing of bifocal contact lens.
- Brand — the brand name of the contact lens.
- Color — it is included if the contact lens change or enhance your eye color (colored contact lens only).
- Cylinder (cyl) — measured in diopters, it shows the extend of your astigmatism (toric lens only).
- Axis — expressed in degrees, it indicates the orientation of the cylinder in the lens to compensate for astigmatism (toric lens only).
Getting a Contact Lens Prescription
To get a lens prescription, you need to see an ophthalmologist or optometrist for a contact lens fitting. The eye doctor will write it for you once you’ve satisfied with fitted, trial contact lenses.
Only after you’ve been fitted and given a contact lens prescription you can legally buy replacement contact lenses. You don’t have to purchase the lenses from the eye care practitioner. But once you wear contacts, the need for regular eye exams and contact lens fittings become more important than before.