People who wear reusable contact lenses are nearly four times more likely to develop a rare eye infection that could rob them of their sight, a study has found.
The British scientists behind the research also warned that wearing lenses in the shower, swimming pools and while sleeping raised the risk too.
In the study, they looked at more than 200 daily or reusable contact lens users who came to clinics with either an eye infection or another illness.
They found Acanthamoeba keratitis (AK) — which inflames the surface of the eye and can lead to blindness — was far more common among those who popped the same lenses into and out of their eyes.
The infection is triggered when the micro-organisms get onto contact lenses via a contaminated solution or dirty hands, and then enter the eye through tiny tears.
Patients suffer eye pain, redness, blurred vision, a cloudy look to the eye and, in severe cases, may end up losing their sight. Treatment includes antiseptics that must be placed directly onto the surface of the eye, possibly for six months to a year.
Pictured above is the cloudy looking eye that can be triggered by an Acanthamoeba keratitis (AK) infection. About 85 percent of cases are among contact lens users (stock image)
Acanthamoeba keratitis: The eye infection that could leave you blind
What is Acanthamoeba keratitis (AK)?
This is an infection of the cornea, or surface of the eye, caused by a micro-organism.
How do I catch the disease?
It is most common among contact lens wearers, but can infect anyone.
The illness is triggered when the micro-organism gets into your eye either via placing contact lenses into your eye with dirty hands, or when in the shower or swimming pool while wearing the lenses.
It then gets into the eye via tiny tears in the surface, and triggers the infection.
What are the symptoms?
Symptoms include blurred vision, a cloudy or dirty looking cornea, eye pain, eye redness, and watery eyes.
These can take several days to weeks to appear following infection.
Does it risk my vision?
If left untreated, the infection can lead to permanent vision loss and total blindness, the CDC says.
Other complications include inflammation of the eye that is painful, and partialy vision loss.
What is the treatment?
Patients are normally offered an antiseptic to help clear the infection from the eye, which is applied directly to its surface.
This may have to be taken for six months to a year.
Patients may also be prescribed antibiotics and, in some cases, could need surgery.
Professor John Dart, an ophthalmologist at the Moorfields Eye Hospital in London, UK, and who led the study, said: ‘In recent years we have seen an increase in Acanthamoeba keratitis (AK).
‘[But] while the infection is still rare, it is preventable and warrants a public health response.’
He added: ‘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.
‘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.’
In the study — pulished in the journal Ophthalmology —, scientists combed through hospital records for an ER department in south-east England for patients with daily or reusable contact lenses.
They found 83 cases of AK that were seen at the unit between January 2011 and August 2014.
They then checked the records for the following year for contact lens users that came in for another illness, unrelated to the infection, and found 122 cases.
Each had also completed a questionnaire on their contact lens type and daily activities.
Results showed that among the 83 AK cases only 20 (24 percent) were daily disposable lens users.
But the other 63 (76 percent) were people that used either soft or rigid reusable lenses.
Statistics showed the risk of developing AK was 284 percent higher among those who used reusable lenses compared to daily lenses.
The scientists also examined whether certain activities made the infection more likely.
Of the 20 AK cases who answered the question on whether they wore lenses in the shower, 12 (60 percent) admitted to this.
For comparison, in the other group it was 25 out of 66 (37 percent)
In the paper, scientists said reusable contact lens users were at greater risk because they were more likely to contaminate their lenses.
On how to reduce the risk, they said lenses should not be worn overnight and contamination of the solution they are stored in should be avoided.
Less than 100 Americans suffer an AK infection every year.
But scientists warn that rates are rising, with more than 85 percent of cases detected exclusively among contact lens users.
Symptoms of the infection take several days to weeks to appear, but include blurred vision, eye pain and eye redness.
The eye may also start to appear cloudy to others, or even feel like there is something inside it.
Patients are normally offered antiseptics that must be applied to the surface of the eye to treat it.
But they can also be prescribed antibiotics or even offered surgery to help handle the infection.
An estimated 45million people in the United States alone wear contact lenses.