Contact lenses are classified as medical devices by the Food and Drug Administration (FDA), not merely cosmetic items. Because they sit directly on the sensitive corneal tissue, their sale is strictly regulated to protect public health. This medical classification means a valid, non-expired prescription is mandatory for purchasing contact lenses, even those worn for color or cosmetic purposes. The prescription can only be issued after a comprehensive fitting process is completed by an eye care professional.
The Legal and Health Requirement for Professional Contact Lens Fitting
The necessity of a fitting is rooted in both patient safety and federal law. In the United States, the Fairness to Contact Lens Consumers Act mandates that prescribers must release a copy of the patient’s complete contact lens prescription upon the conclusion of a successful fitting. This ensures consumers can purchase lenses from any authorized seller, but only after the fitting process is complete.
This requirement protects the eye from complications that can arise from an improper fit. An ill-fitting lens can restrict oxygen flow to the cornea, potentially leading to swelling, inflammation, or the growth of new blood vessels into the corneal tissue. It can also cause discomfort, blurry vision, and corneal abrasions. The fitting process serves as a health safeguard, ensuring the lens interacts safely with the unique biology of the eye.
Essential Measurements Taken During the Fitting
A standard glasses prescription measures only the refractive power needed to correct vision. A contact lens prescription requires additional specifications that dictate the physical interaction between the lens and the eye’s surface. The fitting determines these physiological parameters, including the Base Curve (BC) and the Diameter (DIA) of the lens.
The Base Curve measures the curvature of the back surface of the contact lens, typically ranging from 8.0 to 9.5 millimeters for soft lenses. This measurement is determined using a keratometer or corneal topographer to map the curvature of the patient’s cornea. A smaller BC number indicates a steeper curve, necessary for a more rounded cornea, while a larger number signifies a flatter curve.
The Diameter is the width of the lens from edge to edge, usually falling between 13.0 and 14.5 millimeters for soft lenses. This measurement ensures the lens fully covers the cornea and sits in a stable position. If the diameter is too small, the lens may not cover the cornea adequately, leading to discomfort or vision distortion.
In addition to these measurements, the eye care professional assesses the overall health of the cornea and the quality of the tear film. Tear film evaluation, which may include measuring the tear meniscus or tear break-up time, is essential because poor tear quality can lead to dryness and discomfort with lens wear. This assessment ensures the chosen lens material and design are compatible with the eye’s surface environment.
Navigating the Contact Lens Examination Process
The fitting process involves a series of steps after the initial measurements are taken. Based on the corneal curvature and tear film assessment, the doctor selects trial lenses that are placed on the eye. The fit is then evaluated under a slit lamp microscope to check for proper movement, centration, and coverage. A lens that moves too much can cause blurry vision, while one that is too tight can impede tear exchange and oxygen delivery.
For new wearers, the appointment includes mandatory training on the safe handling of the lenses. This instruction covers the correct technique for insertion and removal, emphasizing washing hands with a non-lotion soap to prevent contamination. Patients are also educated on proper cleaning, disinfection, and replacement schedules to maintain eye health.
The trial wear period is a component of the fitting where the patient wears the lenses at home for a specified time, typically one to two weeks, to test comfort and vision. The patient then returns for a follow-up appointment while wearing the trial lenses. During this final check, the doctor confirms the lens fit is stable, the vision correction is optimal, and the eye tissue shows no negative reaction. Only after this assessment is completed can the eye care professional finalize and release the contact lens prescription.