People who wear reusable contact lenses are nearly four times more likely to develop Acanthamoeba keratitis compared to daily disposable users.
New research by University College London (UCL) has identified multiple factors that increase the risk of Acanthamoeba keratitis (AK), including reusing lenses or wearing them overnight or in the shower.
Acanthamoeba keratitis is an infection of the cornea and is one type of microbial keratitis. The infection is caused by a microscopic organism called Acanthamoeba which is commonly found in bodies of water, such as lakes and oceans and domestic tap water, swimming pools, hot tubs, soil and air; however, findings now indicate that reusable contact lenses can also cause this infection.
Lead author, Professor John Dart (UCL Institute of Ophthalmology and Moorfields Eye Hospital NHS Foundation Trust) said: “In recent years, we have seen an increase of Acanthamoeba keratitis in the UK and Europe, and while the infection is still rare, it is preventable and warrants a public health response.
“Contact lenses are generally very safe but are associated with a small risk of microbial keratitis, most commonly caused by bacteria, and which is the only sight-threatening complication of their use. Given that an estimated 300 million people across the globe wear contact lenses, it is important that people know how to minimise their risks for developing keratitis.”
The growing use of contact lenses
Contact lens usage is now the leading cause of microbial keratitis in patients with healthy eyes in countries in the global north. Whilst sight loss resulting from this is uncommon, Acanthamoeba keratitis is responsible for around 50% of contact lens users who develop sight loss after keratitis. Furthermore, 90% of Acanthamoeba keratitis cases are associated with avoidable risks, and the infection affects less than one in 20,000 contact lens wearers yearly in the UK.
Patients with severe Acanthamoeba keratitis can end up with less than 25% of vision or become blind following the disease and face prolonged treatment. Then 25% of people affected require corneal transplants to treat the disease or restore vision.
Studying contact lenses and Acanthamoeba keratitis
The researchers recruited over 200 patients of Moorfields Eye Hospital who completed a survey, including 83 people with Acanthamoeba keratitis, and compared them with 122 participants who came to eyecare clinics with other conditions and acted as a control group.
Individuals who wore reusable contact lenses had 3.8 times the odds of developing Acanthamoeba keratitis compared to people who wore daily disposable lenses. Showering with lenses increased the odds of Acanthamoeba keratitis by 3.3 times, whilst wearing contact lenses overnight increased the odds by 3.9 times. Furthermore, daily disposable users that reuse their lenses increased their infection risk. A recent contact lens check with a health professional reduced the risk.
Further analysis indicates that 30-62% of cases in the UK, and potentially in other countries, could be prevented if people switched from reusable to daily disposable lenses.
First author, Associate Professor Nicole Carnt (UNSW, Sydney, UCL Institute of Ophthalmology and Moorfields Eye Hospital) said: “Previous studies have linked AK to wearing contact lenses in hot tubs, swimming pools or lakes, and here we have added showers to that list, underlining that exposure to any water when wearing lenses should be avoided. Public pools and coastal authorities could help reduce this risk by advising against swimming in contact lenses.”
