Contact lenses are small, dome-shaped medical devices placed directly on the eye’s surface to correct vision problems such as nearsightedness, farsightedness, and astigmatism. They offer vision correction without frames and are used by millions globally. While the convenience and visual freedom are attractive, not everyone is a suitable candidate. Contact lenses are highly regulated medical devices, and successful use depends on legal requirements, adequate personal hygiene, and underlying eye health. Certain eye conditions, environmental factors, and personal circumstances can prevent their use entirely or limit the available options.
General Prerequisites for Contact Lens Use
Contact lenses are classified as medical devices, and their regulation mandates a current, valid prescription before they can be purchased. This prescription must be specific to contact lenses and cannot be substituted with a regular eyeglass prescription, as the two require different measurements.
A contact lens prescription includes details like the brand, material, base curve, diameter, and the refractive power needed to correct vision. Federal regulations, such as the Contact Lens Rule in the United States, ensure patients receive a copy after a fitting, allowing them to purchase lenses from any seller. The prescription typically expires after one year, requiring a new eye examination to ensure eye health has not changed.
Beyond legal requirements, candidates must demonstrate the maturity and commitment necessary for safe lens handling and maintenance. This includes maintaining excellent hand hygiene, properly cleaning and disinfecting reusable lenses, and adhering strictly to the prescribed wearing and replacement schedule. While there is no specific legal minimum age, eye care professionals assess a younger patient’s responsibility level to minimize the risk of infection from poor compliance.
Medical Conditions That Preclude Contact Lens Wear
Specific chronic or acute eye health issues can make contact lens wear unsafe or impossible. Severe chronic dry eye syndrome is a common contraindication, occurring when the eyes do not produce enough tears or tears evaporate too quickly. Contact lenses float on the tear film and can exacerbate dryness, leading to discomfort, foreign body sensation, and corneal damage.
Active eye infections, such as bacterial or viral conjunctivitis or corneal inflammation like keratitis, immediately disqualify a person from wearing lenses until resolved. Wearing lenses during an infection traps microorganisms against the cornea, worsening the infection and increasing the risk of permanent corneal scarring or vision loss. Severe seasonal or chronic ocular allergies can also cause excessive inflammation and itching, making lens wear irritating and promoting protein and debris deposition on the lens surface.
Anatomical irregularities of the cornea can prevent the successful wearing of standard lenses. Conditions like advanced keratoconus, where the cornea thins and bulges outward into a cone shape, create an irregular surface that standard soft lenses cannot conform to properly. While specialty lenses, such as rigid gas permeable or scleral lenses, can manage these complex cases by vaulting over the irregular cornea, the condition precludes conventional options and requires specialized oversight. Eyelid conditions, like untreated blepharitis, which causes inflammation and bacterial buildup along the lash line, can introduce harmful pathogens to the lens surface and increase the risk of complications.
The Essential Role of Professional Fitting and Follow-Up
Qualification for contact lens wear extends beyond simply having a prescription for refractive error. The required comprehensive eye examination includes a specific contact lens fitting process performed by an eye care professional. This fitting involves precise measurements of the eye’s front surface to ensure the lens rests correctly and comfortably.
A keratometer or corneal topographer measures the cornea’s curvature, determining the necessary base curve. If the lens is too flat, it moves excessively and causes discomfort; if too steep, it restricts oxygen flow and tear exchange, leading to corneal swelling and potential infection. The professional also assesses tear film quality and quantity, which influences the selection of lens material (e.g., hydrogel or silicone hydrogel) to maximize oxygen permeability and hydration.
Following the initial fitting, mandatory training is provided on the proper insertion, removal, cleaning, and disinfection of the lenses. This instructional phase is paramount because improper handling is the leading cause of lens-related eye infections. Regular follow-up appointments are required to monitor the long-term health of the cornea and conjunctiva. These check-ups allow the practitioner to detect early signs of complications, such as corneal neovascularization (the growth of new blood vessels into the cornea due to chronic oxygen deprivation) or giant papillary conjunctivitis (an allergic reaction to lens material or deposits).