UNSW’s Scientia Associate Professor Nicole Carnt is the first-author of a new study showing reusable contact lens wearers are nearly four times as likely to develop a rare sight-threatening eye infection than those wearing daily disposables.
The case control study, published in Ophthalmology and involving UCL and Moorfields researchers in London, also identified multiple factors that increase the risk of Acanthamoeba keratitis (AK) – including reusing lenses, wearing them overnight or in the shower – and highlighted “regulatory deficiencies” that mean online contact lens purchasers may not receive important educational information.
AK is one type of microbial keratitis (MK) that causes the cornea to become painful and inflamed due to infection by Acanthamoeba, a cyst-forming microorganism.
According to the study, contact lens use is now the leading cause of MK in patients with otherwise healthy eyes in countries in the global north. MK-related sight loss is uncommon but Acanthamoeba, although a rare cause, is one of the most severe and is responsible for about half of those contact lens users who develop sight loss after keratitis. In total, 90% of AK cases are associated with avoidable risks, affecting fewer than 1 in 20,000 contact lens wearers per year in the UK.
The most severely affected patients (a quarter of the total) end up with less than 25% of vision or become blind following the disease and face prolonged treatment. Overall, 25% of people affected require corneal transplants to treat the disease or restore vision.
For the study, the researchers recruited more than 200 Moorfields Eye Hospital patients who completed a survey, including 83 people with AK, and compared them with 122 participants who came to eyecare clinics with other conditions, who acted as a control group.
People who wore reusable soft contact lenses (such as monthlies) had 3.8 times the odds of developing AK, compared to people who wore daily disposable lenses.
Showering with lenses increased the odds of AK by 3.3 times, while wearing lenses overnight increased the odds by 3.9 times. Among daily disposable wearers, reusing their lenses increased their infection risk. Having had a recent contact lens check with a health professional reduced the risk.
With further analysis, the researchers estimated that 30-62% of cases in the UK, and potentially in many other countries, could be prevented if people switched from reusable to daily disposable lenses.
Lead author, Professor John Dart from UCL Institute of Ophthalmology and Moorfields Eye Hospital NHS Foundation Trust, said in recent years there has been 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.
“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.”
Carnt, from the UNSW School of Optometry and Vision Science in Sydney, UCL Institute of Ophthalmology and Moorfields Eye Hospital), said previous studies had 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,” she said.
Regulatory deficiencies
The study also highlighted the work regulators and contact lens manufacturers could do to help consumers with safe contact lens practices.
According to the researchers, contact lenses are designated class IIa (low to medium risk) medical devices in the UK and European Union and class II in the US (for reusable daily wear lenses), requiring manufacturers to include essential information on safe use and risks.
However, manufacturers in the UK and European Union are reportedly currently using “an exception to this requirement”, reasoning wearers will have received this information and training from the practitioner who prescribes their lens.
“Now that lenses are available to consumers on the internet without professional involvement (20/85 in this study) in the UK and European Union – but not in the United States – many users may have no training or ongoing education in safe contact lens use.
“In the United Kingdom and European Union, and for soft lenses in the US, information on lens safety and risk avoidance recommendations is absent in lens packaging where the ‘do’s and don’t’s’ needed to reduce the risk of keratitis might be reinforced at each purchase. Instead, users are directed to access ‘Patient information/instruction for use’ guides on contact lens company websites or from their practitioner; these provide variable information about MK risks and risk avoidance.”
Dart said contact lens packaging should include information on lens safety and risk avoidance, even as simple as ‘no water’ stickers on each case, particularly given that many people buy their lenses online without speaking to a health professional.
“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 said.
The study was funded by Fight for Sight, the NIHR Moorfields Biomedical Research Centre and Moorfields Eye Charity.
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