Contact lens wearers have been urged to look after their eyes following an outbreak of a rare infection which can cause blindness.
Moorfields Eye Hospital in London has seen a rise in the number of cases of Acanthamoeba keratitis since 2011.
The preventable infection causes the front surface of the eye, the cornea, to become painful and inflamed and contact lens wearers are most at risk.
What is Acanthamoeba keratitis?
It is an infection of the cornea which is caused by a organism called Acanthamoeba - this is common in many types of water such as rivers and lakes as well as domestic tap water, swimming pools and air.
Are there any signs or symptoms to look out for?
In the early stages, AK and other microbial corneal have similar signs and symptoms which include:
- Sensitivity to light and excessive tearing
- Blurred vision with eye redness and pain
- Sensations of having something in your eye
- Severe headaches
The most severely affected patients are left with less than 25% of their vision or become blind after having the disease.
A study in 2002 estimated the prevalence of Acanthamoeba keratitis in south east England to be 2.5 cases per 100,000 contact lens wearers, but it is currently two to three times higher, researchers from University College London (UCL) and Moorfields Eye Hospital said.
Reusable contact lens wearers with the eye infection are more likely to have used ineffective contact lens solution, have contaminated their lenses with water or to have reported poor hygiene habits, the researchers said.
Showering, swimming and using hot tubs while wearing contact lenses was also a risk factor.
Between 2000 and 2003, eight to 10 cases per year were recorded at the hospital, according to a study published in the British Journal of Ophthalmology.
This rose to between 35 to 65 cases annually from 2011 to 2016.
What have experts said?
Lead author Professor John Dart, from the UCL Institute of Ophthalmology and Moorfields Eye Hospital, said: "This increase in cases highlights the need for contact lens users to be aware of the risks."
Professor Dart said: "People who wear reusable contact lenses need to make sure they thoroughly wash and dry their hands before handling contact lenses, and avoid wearing them while swimming, face washing or bathing.
"Daily disposable lenses, which eliminate the need for contact lens cases or solutions, may be safer and we are currently analysing our data to establish the risk factors for these."
Irenie Ekkeshis, part of Acanthamoeba Keratitis Patient Support Group UK, said: "It is absolutely imperative that regulators and those working in the optical sector take the findings seriously, and use the recommendations to take immediate and urgent action on prevention.
"Contact lenses are medical devices and should be supplied with warnings regarding safe use."