Contact lenses are medical devices used globally to correct vision, offering a popular alternative to eyeglasses. The public often raises questions about the overall safety of these devices, specifically concerning whether they pose a chemical or biological health risk. This inquiry into “toxicity” is complex, extending beyond the material itself to include user habits, care products, and the lens’s eventual disposal.
Material Composition and Chemical Safety
Modern soft contact lenses are predominantly manufactured from two types of polymer: hydrogels (water-containing plastics) and silicone hydrogels. Silicone hydrogels incorporate silicone to significantly increase the amount of oxygen that can pass through the lens to the cornea. Due to their direct interaction with ocular tissue, contact lenses are classified and regulated as Class II or Class III medical devices by the FDA, requiring rigorous testing for safety and biocompatibility before market approval.
All tested contact lenses contain organic fluorine, a chemical marker for per- and polyfluoroalkyl substances (PFAS), also called “forever chemicals.” This organic fluorine is present in concentrations ranging from 105 to 20,700 parts per million (ppm) in common brands. These fluoropolymers are included to improve performance, such as water resistance, but the health implications of chronic exposure are currently not fully understood.
Manufacturers design lenses to be bio-inert, meaning the material should not provoke a reaction from the body. In rare instances, individuals can experience an allergic reaction to a specific component, such as silicone. The lens material can also unintentionally absorb chemicals, including preservatives from care solutions, which are then slowly released onto the eye’s surface. Despite the presence of these compounds, the primary health risks associated with contact lens wear are biological and behavioral.
Biological Risks of Wear
The most severe biological risk for contact lens wearers is microbial keratitis, a sight-threatening infection of the cornea. This condition is overwhelmingly linked to user behavior, with poor hygiene and overnight wear being the most significant risk factors. The lens compromises the corneal surface, and contamination from bacteria like Pseudomonas aeruginosa on unwashed hands or dirty lens cases creates a pathway for severe infection.
Another element is corneal hypoxia, or oxygen deprivation to the eye’s surface. The cornea receives oxygen directly from the air, and the lens creates a physical barrier that restricts this supply. Chronic hypoxia forces the cornea into anaerobic respiration, leading to the buildup of lactic acid and carbon dioxide, a process known as corneal acidosis. This metabolic stress can result in corneal edema (swelling) and, in prolonged cases, neovascularization, where blood vessels grow into the normally clear cornea.
Physical irritation and damage also represent a significant biological risk when lenses are misused. A poorly fitted lens, either too tight or too loose, can cause constant friction against the corneal tissue. This mechanical action can cause a corneal abrasion, a small scratch on the eye’s surface that is both painful and a potential entry point for infectious agents.
The Role of Care Products
Adverse reactions often attributed to the contact lens itself are frequently a sensitivity or allergy to the chemical components within the lens care solutions. Modern multipurpose solutions (MPS) contain chemicals like polyhexamethylene biguanide (PHMB) or polyquaternium-1 (PQ-1) as disinfectants and preservatives. These chemicals, though necessary for killing microbes, can be absorbed by the lens material and then slowly released onto the ocular surface during wear.
This process can lead to solution-induced corneal staining (SICS), a form of toxic keratopathy that causes irritation, redness, and discomfort. The prolonged exposure to the preservative, even in small amounts, can disrupt the corneal cells.
For individuals with high sensitivity, the hydrogen peroxide system is often recommended as an alternative. These systems rely on a 3% hydrogen peroxide solution to disinfect the lenses, offering a preservative-free cleaning option. Since hydrogen peroxide is highly toxic to the corneal tissue, the system requires a neutralizing step, usually involving a platinum-coated disk in a specialized case, before the lenses can be safely inserted. Skipping this neutralization process can cause an immediate chemical burn to the eye’s surface.
Environmental Impact of Disposal
The definition of “toxic” can also be extended to the environmental harm caused by improper disposal of contact lenses. A significant number of wearers, estimated at 15 to 20 percent, dispose of their used lenses by flushing them down the toilet or sink. Contact lenses are made from soft plastics that are denser than water and do not biodegrade easily within wastewater treatment facilities.
The mechanical processes at the treatment plants cause the lenses to fragment into smaller pieces, creating microplastics. These microplastics are often discharged with treated water into waterways or remain in the sewage sludge, which is frequently spread on land as fertilizer. This improper disposal introduces plastic pollution into the environment, where it can be ingested by aquatic life and enter the food chain. To mitigate this environmental issue, used lenses should be placed directly in the regular trash, or users can participate in specialized recycling programs.