Misuse of contact lenses (wearing them too long, not cleaning them properly) causes 1 million eye infections/yr in US. "Contact lenses offer many benefits, but they are not risk-free. Keratitis can be a scary infection, but it is preventable if people follow healthy habits and take care of their eyes and their lenses". Some bad habits, such as sleeping with contact lenses, failing to clean and replace lens solution frequently, and letting contact lenses get wet while swimming or in the shower, greatly raises the risk for keratitis. People who wear their contact lenses overnight are more than 20 times more likely to get keratitis. http://buff.ly/1xw4iSn

A few basic 'contact lens hygiene' measures can keep patients free of keratitis -- Keratitis and Contact Lens Use - CDC, YouTube: