People who wear reusable contact lenses are at higher risk of contracting a rare but serious eye infection than those who use daily disposable contacts, a new study published in the journal Ophthalmology finds.

Experts say the report is a warning to contact lens wearers to practice good hygiene.

The study from a team of researchers from University College London and Moorfields Eye Hospital reports that reusable contact lens wearers were almost four times as likely to contract Acanthamoeba keratitis (AK) than users of disposable contacts.

“Contact lenses cause microabrasions and disruption of the epithelium of the cornea, the front layer of the front of the eye,” Dr. Yuna Rapoport, an ophthalmologist with Manhattan Eye in New York, told Healthline. “This makes the cornea more susceptible to any pathogens that are opportunistic… Basically, contact lenses change and decrease the integrity of the corneal epithelium and Acantheomeba adheres to an irregular cornea easier as well as a contact lens surface, thus increasing the risk of keratitis in contact lens wearers.”

The study findings were based on a comparison between 83 Moorfields Eye Hospital patients with AK and a control group of 122 people with other eye conditions.

Overall, the risk of developing AK was 3.8 times higher among reusable contact wearers, according to researchers. They estimated that 30 to 62 percent of AK cases could be prevented by switching from reusable to daily disposable lenses.

“If economically feasible switching to daily disposables eliminates some of these risk factors,” Dr. Alexander Solomon, a surgical neuro-ophthalmologist and strabismus surgeon at the Pacific Neuroscience Institute at Providence Saint John’s Health Center in California, told Healthline.

Solomon also advised wearing glasses when possible to minimize the risk of infection from contacts.

“I found that when I stopped using my contact lenses regularly, switching to the daily disposables became more affordable and was by far the safer option,” he said.

AK is a microbial infection of the cornea, the clear protective outer layer of the eye. Infections by Acanthamoeba, can cause corneal cysts.

Symptoms include pain and inflammation of the cornea. About one in four people with AK suffer serious vision loss, defined as retaining less than 25 percent of their vision after infection. A similar number require a corneal transplant to restore or improve their vision.

AK itself is rare, but about 85 percent of cases in the United States occur in people who wear contact lenses.

More than 90 percent of AK cases can be traced to preventable causes, the study researchers noted.

For example, showering with lenses increases the odds of developing AK by 3.3 times, researchers found, while wearing lenses overnight raises the risk by 3.9 times.

“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,” noted Dr. Nicole Carnt, first author of the study and an assistant professor at the University of New South Wales and affiliated with the UCL Institute of Ophthalmology and Moorfields Eye Hospital, in a press statement.

Dr. Benjamin Bert, an ophthalmologist at MemorialCare Orange Coast Medical Center in California, told Healthline that contact lenses “act as a sponge” when in contact with fluids that can potentially contain the pathogen.

“Being stuck to the contact lens and then placed against the cornea gives the acanthamoeba more time in contact with the surface of the eye to begin to allow penetration into the cornea,” he said. “Without a contact lens in place you simply blink away the water and the acanthamoeba with it, greatly reducing the risk of having an infection.”

Using daily disposable lenses, while safer than reusable contacts, is not risk-free.

AK infections were found to be more common among wearers of disposable contacts who reused their lenses instead of discarding them after daily use, for example.

“Storing the lenses incorrectly, mishandling the lenses, and overwearing lenses decreases the oxygen that the cornea receives and makes the infection of acanthamoeba even more possible,” said Rapoport.

“And absolutely do not leave them out to dry and lick them to add moisture before putting them back in your eye — this is more common than you may think,” added Dr. James Dello Russo, an optometrist and ophthalmologist at the New Jersey Eye Care Center.

“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,” said Dr. John Dart, the lead study author and a consultant opthalmologist at the UCL Institute of Ophthalmology and Moorfields Eye Hospital NHS Foundation Trust in London, in a press statement.

“Anyone who wears contact lenses and who experiences decreased vision, eye redness, or eye pain should remove the lenses and seek care with their optometrist or ophthalmologist,” said Dr. Kathryn Colby, chair of the Department of Ophthalmology at NYU’s Grossman School of Medicine, told Healthline.

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