These days, it’s safe to say that everyone either wears contact lenses or knows someone who does and understands that it’s important to change your contacts frequently. As if it isn’t annoying enough to have to dig your fingers into your eyeballs each morning and night, you also have to stay on top of keeping the contact solution fresh and the supply of new contacts steady. Regardless of whether someone has one-day-use or another type of contacts that can be left in longer, doctors warn of the importance of switching pairs regularly. But why change them so often? Why not just save money and wear the contacts a little longer, especially if they aren’t scratched? Is it really so bad to have irritated eyes for a few days?
Irritation is not the only effect of leaving contact lenses in too long- it can also lead to the growth of an organism called Pseudomonas aeruginosa. Though P. aeruginosa primarily affects patients in hospitals or with weakened immune systems, it can also cause problems in healthy patients, like rashes on the skin when hot tubs are inadequately chlorinated and eye infections with extended-use contact. Only requiring acetate and ammonia as its source of carbon and nitrogen, P.aeruginosa is an opportunistic pathogen, meaning it can easily adapt to survive in many different environmental conditions and can make use of a wide range of available nutrients. Though it commonly affects plants like lettuce, tomatoes, and tobacco, P.aeruginosa forms slime-enclosed communities called biofilms that allow it to survive and grow within human tissues. These biofilms prevent antimicrobial agents and other antibiotics from entering the community of bacteria within. This form of defense allows the organism to be resistant to antimicrobial agents found in hand creams, and certain cleaning solutions, like those in contact solutions.
Irritation from wearing contact lenses for an extended period of time can lead to inflammation and infection, called microbial keratitis. Though many bacterial organisms’ growth can lead to microbial keratitis, the most common source is P. aeruginosa. Once in the eye, P. aeruginosa has the ability invade and kill corneal cells. It can also activate several pathways in the immune system which are used to alert the body of the source of inflammation and recruit white blood cells. Despite the fact that white blood cells usually fight infection within the body, the buildup of white blood cells can lead to the destruction of healthy corneal cells and other tissues within the eye, ultimately leading to scarring and vision loss.
Pseudomonas aeruginosa is not only responsible for causing eye irritation from the use of old contacts, it also has the ability to withstand varying environmental conditions with minimal nutrients allowing it to grow and multiply in environments practically devoid of nutrients. This includes distilled water and anaerobic environments, as well as those with higher temperatures of up to 42°C (107.2°F). The elevated temperature levels and churning water of hot tubs causes the chlorine levels in the water to drop and allow the resulting higher pH of the water to reduce the antibacterial effect of the halogens in the chlorine. If the chlorine level drops below <1mg/L P. aeruginosa can multiply up to 1,000,000 organisms per milliliter of water in as short a window as 24hours. The organism can enter the body through the gastrointestinal tract due to the accidental ingestion of water and spread to warmer moist areas of the body, like the perineum and armpits, and form a rash.
Laboratories like Gibraltar Laboratories use the antimicrobial effectiveness test to test the antimicrobial properties of hand creams and optic solutions such as contact solutions over time. This helps to prove how strong the antimicrobial agents in these products are in preventing the growth of harmful bacteria like P. aeruginosa. Though there are antibiotics like fluoroquinolone that can be used to combat P. aeruginosa, the organism is known for its ability to resist antibiotics and to even mutate to survive once an antibiotic has already been introduced. That being said, it’s not a pleasant organism to contract.
So the doctors are right- spend the extra money and make sure you and your friends aren’t keeping contacts in for too long and are changing the solutions regularly.
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