Contact lenses (CLs) offer a convenient alternative to traditional eyeglasses for correcting vision. While these medical devices are widely used and generally effective, they are not without risks, particularly if wearers do not follow proper care instructions. Misuse can expose the eye to complications, some of which may lead to vision loss.
The Primary Danger: Infection Risk
The most severe and vision-threatening complication associated with contact lens wear is microbial keratitis, which is an infection of the cornea. Wearing a contact lens can alter the ocular surface environment, creating a space between the lens and the cornea where pathogens can become trapped and multiply. This effect, combined with micro-abrasions that may occur during lens insertion or removal, provides a pathway for bacteria and other microbes to invade the corneal tissue.
Bacteria, especially Pseudomonas aeruginosa and Staphylococcus aureus, are the most common cause of contact lens-related keratitis, often leading to rapid and painful infections. Less frequent, but often more severe, infections are caused by fungi, such as Fusarium, and the microscopic parasite, Acanthamoeba. These pathogens typically gain access to the lens surface from external sources, with poor hygiene practices being the primary culprit.
Exposure to non-sterile water is a major risk factor, as tap water and hot tubs can harbor Acanthamoeba and other harmful microorganisms. Failing to clean the case regularly or “topping off” old solution allows bacteria to form a biofilm on the case and lens surface. Once an infection takes hold, it can cause corneal scarring, potentially resulting in permanent vision impairment or the need for a corneal transplant.
Non-Infectious Physical Stress on the Cornea
Beyond the risk of microbial invasion, the physical presence of a contact lens can induce non-infectious stress on the corneal tissue. The cornea lacks blood vessels, receiving most of its oxygen directly from the air. When a contact lens covers the cornea, it acts as a barrier, reducing the oxygen supply and leading to corneal hypoxia.
Corneal hypoxia causes the tissue to swell, known as edema, and can trigger the development of tiny fluid-filled pockets called microcysts within the cornea. Over time, persistent oxygen deprivation can stimulate the growth of new blood vessels, a condition called neovascularization, which grow into the clear cornea in an attempt to restore the oxygen supply. This abnormal vascularization can compromise vision.
Deposits that accumulate on the lens surface can cause mechanical and inflammatory issues. Poorly fitting or dirty lenses can lead to corneal abrasions or erosions—physical scratches on the outermost layer of the cornea. Some wearers develop Giant Papillary Conjunctivitis (GPC), an inflammatory allergic reaction to protein deposits that results in large, raised bumps on the inner surface of the eyelid.
Essential Practices for Safe Contact Lens Use
Mitigating the risks of infection and physical stress requires strict adherence to a prescribed care routine and wearing schedule. Always wash hands thoroughly with soap and water and dry them with a lint-free towel before handling lenses to prevent the transfer of pathogens. Never use tap water, saliva, or any non-sterile liquid to clean or store contact lenses, as water is a known source of dangerous microorganisms like Acanthamoeba.
Lenses must be cleaned using a “rub and rinse” technique with fresh, prescribed disinfecting solution, even if the solution claims to be a “no-rub” formula. The lens case should be emptied, rinsed with fresh solution, air-dried upside down after each use, and replaced every three months. Wearers must follow the schedule given by their eye care professional, never sleeping in lenses unless approved for extended wear, and never wearing them past the recommended replacement date.
Regular eye examinations are necessary to ensure the lenses fit correctly and to monitor the cornea for early signs of hypoxia or inflammation. If any symptoms occur, such as unusual redness, pain, blurred vision, or sensitivity to light, the lenses must be removed immediately. If symptoms persist, the wearer should seek prompt medical attention, as these symptoms can indicate a developing infection or serious corneal complication.