Here’s an eye-opener: 99 percent of people who wear contact lenses are guilty of at least one risky behaviour that can set the stage for serious eye infections, finds a recent study from the Centres for Disease Control and Prevention (CDC).

If you wear contacts, you probably already know which sins can damage your eyes. “But the reason these behaviours are so prevalent is because people can get away with them many times before something bad happens,” says Keith Walter, M.D., an ophthalmologist at Wake Forest Baptist Medical Centre.

Contact Crime 1. Sleeping in Your Lenses

The problem: Lenses are barriers that can starve your cornea of oxygen, causing the cells on its surface to break down. When you close your eyes to nod off, “you create a warm, dark, moist environment with very little oxygen, which bacteria and fungus love,” says Dr. Walter.

Yes, it can be a pain to remove and rinse your contacts before you fall asleep every night—especially if you take an unexpected nap. But that’s simply what you have to do to avoid infection. File it under advice you may not like, but that you follow for your own—same as “don’t yell at anyone at work.”

Contact Crime 2. Topping Off Your Solution

When you squirt new liquid into your contacts case without dumping out the stuff that’s already there, you dilute the disinfecting solution. As a result, you don’t get as much cleaning power overnight.

Plus, the longer you leave old solution in the lens case while you’re wearing your contacts, the more time you give gross organisms the opportunity to grow inside.

The fix is a no-brainer: Rinse your case with contact lens solution, empty and wipe it dry with a clean tissue, and add fresh solution every time you put your lenses in there, Dr. Walter says. Replace your case at least every 3 months to keep bacteria at bay.

Contact Crime 3. Rinsing Your Contacts in Tap Water

Ever rub your eyes because they’re itchy, and one of your contacts accidentally falls out? If you don’t have your solution handy, you probably rinse the lens off in the nearest water you can find. We’ve certainly done this in a pinch.

But it’s a bad idea. Tap water can contain an amoeba that has been known to cause Acanthamoeba keratitis, a hard-to-treat eye infection, says Dr. Walter.

This condition inflames your cornea and can lead to scarring and impaired vision. Even filtered water from your sink can be an issue, because bacteria may grow on the faucet, enter into the water, and get on your lenses.

Ultimately, there’s only one liquid you should put on your lenses: disinfecting solution, says Dr. Walter. So if your lens pops out and drops to the ground, you’ll need to toss it in the trash.

There’s an obvious and easy way to avoid all of the cleaning issues associated with contacts: Move to a daily wear product. And then do just that—wear them for one day only, and toss them before bed. It’s ideal because you get a fresh pair of lenses every morning.

The downside, of course, is that daily contacts aren’t as economical as monthly-wear lenses. If you can afford them, consider the option. But if you can’t, just be extra diligent about taking care of your regular pair.

Contact Crime 4: Wearing the Same Lenses Too Long

Whether your contacts call for daily, weekly, or monthly replacements, you need to swap them as often as the package indicates, Dr. Walter says.

Sounds obvious, but half of all lens wearers don’t adhere to their schedule, according to the CDC report.

We get it: Squeezing a couple extra days out of your pair could save you a few bucks, or maybe you simply forget to make the change.

But if you keep your contacts in for too long, you might experience irritation, infections, and corneal ulcers—extremely painful open sores on your eye that can cause long-term vision damage, says Dr. Walter.

And last we checked, your eyes aren’t irreplaceable. So why would you ever put them at risk?