Contact lenses are thin, medical-grade devices placed directly on the surface of the eye to correct vision or change eye color. All contact lenses, even those with no vision correction, require a valid prescription from an eye care professional. This requirement is in place primarily to protect the health of your eyes.
The Legal Requirement for a Prescription
The requirement for a prescription is mandated by federal law because contact lenses are regulated medical devices. In the United States, the Fairness to Contact Lens Consumers Act (FCLCA), signed into law in 2003, dictates the rules for the sale of all contact lenses. This legislation ensures that a valid, unexpired prescription is required for any purchase, whether the lenses are bought in-person or from an online retailer.
This legal mandate applies to all types of lenses, including decorative or “plano” lenses worn solely for cosmetic purposes. Retailers are prohibited from selling lenses without verifying the prescription with the prescribing eye care practitioner. The law also guarantees that a patient receives a copy of their prescription at the end of a fitting.
If a seller attempts to verify the prescription and the prescriber fails to respond within eight business hours, the seller is legally allowed to fill the order. Any advertising that suggests contact lenses can be obtained without a prescription is prohibited under the law.
Why Contact Lenses Are Classified as Medical Devices
Contact lenses are classified as medical devices by the Food and Drug Administration (FDA) because they physically interact with the delicate tissue of the eye. The lenses rest directly on the cornea, which requires a constant supply of oxygen from the air to remain healthy since it lacks its own blood vessels.
An improperly fitted lens can restrict the flow of oxygen to the cornea, a condition known as hypoxia. Hypoxia can lead to corneal swelling, increased susceptibility to infections, and potentially irreversible damage like corneal neovascularization. Lenses that do not fit correctly can also cause mechanical irritation, leading to corneal abrasions or ulcers.
Wearing lenses that are not professionally fitted significantly increases the risk of serious eye infections, such as keratitis, an inflammation of the cornea. These infections may result in severe pain, blurred vision, or permanent scarring or vision loss if not treated promptly. The precise measurements taken during a fitting ensure the lens allows for proper tear exchange and maintains a healthy corneal environment.
Essential Components of a Contact Lens Prescription
A contact lens prescription is fundamentally different from a glasses prescription because it includes specific parameters related to the lens’s physical fit on the eye. These measurements are determined during a professional fitting and are necessary to avoid the safety risks associated with an improper fit. A glasses prescription only specifies the corrective power, which may differ for contacts since they sit directly on the eye’s surface.
The prescription contains several key parameters:
- Power or Sphere (PWR/SPH): This is the corrective strength measured in diopters. A minus sign indicates correction for nearsightedness (myopia), while a plus sign signifies correction for farsightedness (hyperopia).
- Base Curve (BC): This value, typically in millimeters, dictates the curvature of the lens to match the natural curve of the cornea. A lower BC means a more curved fit.
- Diameter (DIA): Measured in millimeters, this determines the overall width of the lens, ensuring it covers the appropriate area of the eye.
- Brand and Material: Specifies the exact lens type, as different materials have varying levels of oxygen permeability and water content.
- Cylinder (CYL) and Axis (AX): These parameters are included for patients with astigmatism to correct for the eye’s irregular shape.
Prescription Validity and Renewal
Contact lens prescriptions are not permanent and have a defined expiration date to ensure ongoing eye health and safety. The Fairness to Contact Lens Consumers Act mandates that prescriptions must be valid for a minimum of one year from the date of the last eye exam and fitting. Some states may allow for longer validity periods, up to two years, but a prescriber can shorten the expiration date if there is a medical reason related to a patient’s ocular health.
Renewal requires a comprehensive eye examination and a new contact lens fitting to assess the health of the cornea and surrounding tissues. Vision can change over time, and continuing to wear an old prescription may lead to eye strain, irritation, or blurry vision. The annual exam allows the eye care professional to check for early signs of corneal issues or changes in vision.
Using an expired prescription is not legally permitted for purchasing new lenses, even if a patient feels their vision has not changed. This mandatory renewal process protects the patient from the long-term risks associated with wearing an ill-fitting or inappropriate lens.