People who wear reusable contact lenses are almost four times more likely to develop a rare sight-threatening eye infection than those who wear daily disposable lenses, according to a study led by UCL and Moorfields researchers.
The case-control study, published in Ophthalmology , identifies multiple factors that increase the risk of Acanthamoeba keratitis (AK), including reusing lenses or wearing them overnight or in the shower.
AK is a type of microbial keratitis (corneal infection), a condition that causes inflammation of the cornea (the clear, protective outer layer of the eye).
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 in Acanthamoeba keratitis in the UK and Europe, and although 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, which is the only sight-threatening complication of their use. With approximately 300 million people worldwide wearing contact lenses, it is important that people know how to minimize the risks of developing keratitis.”
Contact lens wear is now the leading cause of microbial keratitis in patients with otherwise healthy eyes in countries of the global north. Vision loss as a result of microbial keratitis is rare, but Acanthamoeba, although a rare cause, is one of the most serious and is responsible for approximately half of contact lens wearers who develop vision loss after keratitis. 90% of AK cases are associated with avoidable risks, although the infection remains rare, affecting less than 1 in 20,000 contact lens wearers per year in the UK.
AK causes the front surface of the eye, the cornea, to become painful and inflamed due to infection by Acanthamoeba, a cyst-forming microorganism. The most severely affected patients (a quarter of the total) end up with less than 25% vision or go blind after the disease and face prolonged treatments.
Overall, 25% of affected people require corneal transplants to treat the disease or restore vision.
For the study, researchers recruited more than 200 Moorfields Eye Hospital patients who completed a survey, including 83 people with AK, and compared them to 122 participants who attended eye care clinics with other conditions, who acted as a control group. .
People who wore reusable soft contact lenses (such as monthly lenses) were 3.8 times more likely to develop 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 the risk of infection. Having a recent contact lens checkup with a healthcare professional reduced the risk.
With further analysis, the researchers estimated that between 30% and 62% of cases in the UK, and potentially many other countries, could be prevented if people switched from reusable lenses to daily disposables.
A recent study led by Professor Dart found that AK is increasing in prevalence in the UK. Reviewing incidence data from Moorfields Eye Hospital from 1985 to 2016, he and his team found an increase from 2000-2003, when there were eight to 10 cases per year, to between 36 and 65 cases annually at the end. of the study period. .
First author Associate Professor Nicole Carnt (UNSW, Sydney, UCL Institute of Ophthalmology and Moorfields Eye Hospital) said: "Previous studies have linked AK to contact lens use in hot tubs, swimming pools or lakes, and here we have added showers to that." she lists, stressing that exposure to water should be avoided when wearing lenses. “Public swimming pools and coastal authorities could help reduce this risk by discouraging swimming with contact lenses.”
Professor Dart added: "Contact lens packaging should include information about lens safety and risk prevention, 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 toward preventing infection, such as washing and drying your hands thoroughly before inserting lenses.”
The study was funded by Fight for Sight, the NIHR Moorfields Biomedical Research Center and Moorfields Eye Charity. https://www.aaojournal.org/article/S0161-6420(22)00594-2/fulltext
