Wearing reusable contact lenses could increase the risk of getting eye infections, including a rare sight-threatening infection, experts have warned.

A group of researchers from University College London (UCL) and Moorfields found that people who wear reusable contact lenses are nearly four times as likely to develop the eye infection as those who wear daily disposable lenses.

The study found a number of factors that increase the risk of developing acanthamoeba keratitis (AK), a type of corneal infection that results in the inflammation of the cornea.

These factors included reusing lenses, wearing them overnight, or wearing them in the shower.

According to lead author, Professor John Dart of the UCL Institute of Opthalmology and Moorfields Eye Hospital, the infection is rare but the fact that around 300m people wear contact lenses, more awareness is needed around the issue.

“In recent years we have seen an increase of AK in the UK and Europe, and while the infection is still rare, it is preventable and warrants a public health response,” he said.

“Contact lenses are generally very safe but are associated with a small risk of microbial keratitis (corneal infection), most commonly caused by bacteria, and which is the only sight threatening complication of their use.

“Given that an estimated 300m people across the globe wear contact lenses, it is important that people know how to minimise their risks for developing keratitis,” he added.

In the UK, AK infections affect fewer than one in 20,000 contact lens wearers per year. However, 90 per cent of cases are avoidable.

Sight loss due to corneal infections is uncommon but AK is one of the most severe eye infections a person could develop.

The study, published in the journal Opthalmology, recruited more than 200 patients from Moorfields Eye Hospital and asked them to complete a survey. Of these, 83 people had AK and were compared to 122 patients who has other conditions, as a control group.

The researchers found that people who wore reusable contact lenses, like monthlies, were 3.8 times more likely to develop AK compared to people who wore disposable lenses.

Wearing contact lenses while showering increased the risk of AK by 3.3 times, while wearing them overnight to sleep increase the risk by 3.9 times.

Of those who wore daily disposable lenses, reusing the lenses also increased their infection risk.

Experts estimated that between 30 to 62 per cent of cases in the UK could be prevented if people switched from reusable to daily disposable lenses.

Associate Professor Nicole Carnt, first author of the study, 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.”

Prof Dart added that contact lens manufacturers should include lens safety and risk avoidance information on the packaging, especially because many people buy contact lenses online.

“Basic contact lens hygiene measures can go a long way in avoiding infections, such as by thoroughly washing and drying your hands before putting in your lenses,” he advised.

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