Reusable Contact Lenses Linked to Rare Eye Infection Causing Blindness
People who wear reusable contact lenses are almost four times more likely to develop rare sight-threatening eye infection than those wearing disposable lenses, according to a study led by UCL and Moorfields researchers.
Reusing lenses, wearing them overnight, or using them while in the shower are just a few of the factors that raise the risk of Acanthamoeba keratitis (AK), according to a case-control study that was published in the journal Ophthalmology.
Acanthamoeba keratitis is one type of microbial keratitis (corneal infection)—a condition that causes inflammation of the cornea.
"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 minimize their risks for developing keratitis,” said Lead author Professor John Dart (UCL Institute of Ophthalmology and Moorfields Eye Hospital NHS Foundation Trust).
Contact lens use is currently the main reason causing microbial keratitis in patients with otherwise healthy eyes in countries in the global north.
Even though Acanthamoeba is a rare cause of keratitis caused by microorganisms, it is one of the most severe and accounts for roughly half of all cases of sight loss experienced by contact lens wearers.
Although the illness is still rare, affecting less than 1 in 20,000 people who wear contact lenses annually in the UK, up to 90% of AK cases are linked to preventable risks.
The study
For the study, the researchers gathered over 200 Moorfields Eye Hospital patients to participate in a survey, including 83 with AK. They then compared these individuals to 122 others who visited eye care clinics with different medical problems and served as the control group.
Reusable soft contact lens wearers (such as monthly wearers) had a 3.8 times higher risk of developing AK compared to daily disposable lens wearers. Wearing lenses overnight increased the risk of AK by 3.9 times, whereas showering with lenses in increased the risk by 3.3 times.
The risk of infection rose when daily disposable lens wearers reused their lenses. The danger was lower if you recently had your contact lenses checked by a medical expert.
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.
AK is becoming more common in the UK
According to a recent study conducted under Professor Dart's direction, AK is becoming more common in the UK. He and his team discovered an increase starting in 2000-2003, when there were eight to ten cases per year, to between 36 and 65 annual cases at the end of the study period by looking at incidence data from Moorfields Eye Hospital from 1985 to 2016.
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."
Professor Dart added, "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."
