People sometimes clean their lenses with public water or get water in their lenses when they swim—but this increases the risk of an infection of Acanthamoeba Keratitis.
Researchers at University College London say they have seen a threefold increase in cases since 2011 and contact lens wearers are more likely to get infected, usually because of poor hygiene.
People who don't follow good hygiene practices—such as not using a good cleaning solution, or showering, washing or swimming while wearing the lenses—are three times more likely to get infected, the researchers say. Although the risk is greater for those who use reusable contacts, it's still there for those who use daily disposables.
Trying to understand why some became infected, the researchers discovered that hygiene was the key factor. "People who wear reusable contact lenses need to make sure they thoroughly wash and dry their hands before handling contact lenses and avoid wearing them while swimming, face washing or bathing," said Prof John Dart, one of the researchers.
Cases are rare, although they have increased from 10 to up to 65 a year in the UK in the past few years. It affects just 2.5 people in every 100,000 contact lens wearers, and around a quarter of those infected could go blind. In some cases, a corneal transplant is possible.