context: Contact lenses are a convenient and comfortable alternative to eyeglasses for many people. But you can't wear them all the time. And if you don't clean and care for them correctly, you're more likely to get eye infections. People who wear contact lenses have a higher risk for keratitis, an infection of the cornea, the clear outer covering of your eye. They're also called corneal ulcers. Viruses, bacteria, fungi, and a rare but serious eye parasite can cause keratitis. It's also easier for you to catch pinkeye, or conjunctivitis, when you wear contacts. These infections come from a bacteria or virus in the thin membrane covering the white part of your eye and the inside of your eyelids. Stop wearing your contact lenses immediately if you have these symptoms: Redness Swelling Extra tears or sticky, gooey stuff from your eye Blurry vision Light sensitivity Itching, burning, or a feeling that something's in your eye Eye pain Call your eye doctor as soon as possible. Some problems can be quite serious and need treatment right away to save your sight. Don't throw your lenses away. Put them in the case, and bring them when you see your eye doctor. They may give him or her a clue about what's wrong since cultures are sometimes taken off contact lenses to determine what is causing the infection. These symptoms could also be an allergic reaction to the lenses themselves or to another irritation in your eyes, like pollen. The "normal" bacteria on our skin, mouth, and nose usually don't cause any harm. But the combination of a lot of them on your contact lenses and any small scrape on your eye can be very dangerous. About a third of people have Staphylococcus aureus in their nose. It's easily spread to your eyes by your hands, and it's stubborn and hard to treat. Wash your hands and keep your contacts sterile to avoid an eye infection from it. Pseudomonas aeruginosa is a bacteria that can cause a fast-moving infection of your cornea and leave a hole in your eye. You could lose your vision permanently. Make sure you clean and disinfect your lenses and lens case correctly, and don't keep either longer than you should. Mild bacterial infections of the eye surface usually clear up after treatment with antibiotic eyedrops. The herpes simplex virus -- both the kind that causes cold sores and the kind responsible for the STD -- can cause keratitis. You can transfer it if you touch an active herpes sore and then touch your eye. Viruses that cause upper respiratory infections and the chickenpox virus can also infect your cornea. Pinkeye most often comes from the common cold virus. A virus can easily spread to your other eye or to someone else. You'll probably have to wait out a viral infection, but you can ease your symptoms with a cool compress and artificial tears. Your doctor may recommend steroid eyedrops to ease swelling, too. Tiny one-celled animals called acanthamoeba live in water, including tap water, swimming pools, and hot tubs. They can infect your eye more easily if you're wearing contacts while you're in the water. If you wear contacts, avoid opening your eyes in a hot tub where this parasite is typically found. They're also the reason you shouldn't use water -- even distilled or bottled water -- to clean and store your contacts. Keratitis caused by these parasites is very hard to treat. You may need a cornea transplant. It doesn't happen often, but you can get fungal infections in your eye. These can lead to blindness. They're usually treated with antifungal eyedrops or pills. Lower your risk of an eye infection by following these guidelines: Don't reuse or "top off" cleaning solution. Use fresh solution every day. Keep your lens case clean. Replace it every couple of months. Wash your hands often, especially before you handle your contacts. Take out your lenses, even extended-wear ones, before you go to sleep. Don't wear your contacts in the shower, bath, or hot tub. Take them out before you go swimming. Read the labels and follow directions on your lenses and contact cleaning solution. Don't sleep in your contact lenses.