1. Taking a shower or a swim in your contacts
It might seem like no big deal, but swimming and showering with your contacts in is a bad idea, says Steinemann. Most water sources – including lakes, pools, hot tubs, and bathroom sinks – contain the microorganism Acanthamoeba. If it finds its way into your eyes, acanthamoeba can cause an extremely painful infection and potentially even lead to blindness. The treatment is long and difficult, Steinemann says.
Contact lens wearers are at greater risk for a number of reasons (the same Journal of Optometry paper says that contact lenses may account for 95 percent of acanthamoeba eye infections). The acanthamoeba is particularly attracted to the contact lens: Contacts cause minor scratches on the cornea, which make it more vulnerable to bacteria and microorganisms of all kinds. In addition, any bacteria living on the surface of the contact serve as a food source for the acanthamoeba, allowing it to survive in your eye.
2. Using water to clean your lenses
Even riskier than swimming while wearing contacts is storing your lenses in tap water. “Even though tap water is pure enough to drink, it’s not sterile,” Steinemann says. Acanthamoeba also lives in tap water, so soaking lenses in water from the sink is an invitation to infection. Instead, you should always store them in solution.
It’s also important to wash your hands before putting your lenses in and taking them out – and never leave old solution from the day before in the case (use all new solution, don’t just top it off). Rub and rinse the contacts with solution after each use.
3. Using a case for too long without replacing it
Steinemann recommends cleaning your lens case thoroughly with solution every day, and replacing the case every month. (The American Optometric Association advises replacing it at least every three months.)
And don’t cut corners by throwing your contacts case in the dishwasher: “There’s food in your dishwasher. It’s not like it’s a sterile place,” says Dr. Anne Sumers, an ophthalmologist and spokesperson for American Academy of Ophthalmology. Steinemann also warns against putting your case in the dishwasher, citing concerns about the residues from dish soap that could end up on the case or lens. Clean the case with solution and let it air dry until the next day.
This may sound complicated, but it’s important. An old case is “a set up for germs growing on the case and on the lens,” Steinemann says. Besides the general griminess of a six-month-old contact case that you can probably see, invisible germs and bacteria are likely living there, too.
And keeping contacts and their cases clean and bacteria-free reduces vulnerability to all types of infection. A 2012 study in the journal Ophthalmology showed that the risk of eye infection was 6.4 times greater in those who didn’t properly clean their contact cases and 5.4 times greater in those who didn’t replace their cases frequently enough.
4. Wearing your contacts way past their expiration date
“Most people will admit that they keep their lenses longer,” Steinemann says, than the recommended period. This is a similar hazard to a worn-out case: Old lenses become coated with germs and the build-up of solution, proteins, and other residues, Steinemann says. This will make the lenses uncomfortable and can lead to infection.
5. Sleeping in your contacts
Although some professionals and contact manufacturers say that it’s okay to sleep in certain types of lenses, Steinemann does not recommend it. Your cornea, the outside layer of your eye that the contact covers, needs oxygen. Wearing contacts deprives the eye of that oxygen, and sleeping in your lenses exacerbates the problem. At best, overnight wear will likely cause irritation and discomfort. At worst, it could lead to a serious infection. According to an overview of surveys by the Journal of Optometry, sleeping in contact lenses seemed to be “the main cause of microbial keratitis,” a type of eye infection.