It's that time of year when you can finally start swimming outside, but doctors are warning people to protect their eyes when they're swimming because they could get an infection that can lead to blindness in some cases.The infection is from a type of amoeba called Acanthamoeba keratitis, or AK, which is the subject of a recent study by the University of Iowa Hospitals and Clinics. According to the study, AK is difficult to kill.The study found that, while AK is still rare, the chances that someone becomes infected with it in Iowa are much greater than researchers initially thought.This is especially true for people who wear contact lenses.The amoeba lives in dirt and water, so people can come into contact with it, especially in open bodies of water such as lakes and rivers.Eye doctors recommend that people remove contact lenses before swimming or showering, and never rinse lenses with tap water."The biggest symptom is pain, just lots of eye pain," said Dr. Kacie Monro, an optometrist with Dr. D.M. Fitzgerald and Associates in Cedar Rapids. "The eye will be red. The vision will be blurry. The eye might be a little bit goopy."