Cases of eye infection with a type of amoeba called Acanthamoeba – which can irreparably damage the corneas – have doubled since 2010, said Professor John Dart, of Moorfields Eye Hospital in London.
He said the trend towards internet purchasing had contributed to the rise, because people do not undergo ‘vital’ eye checks so frequently.
These are essential for spotting early signs of infection and to make sure people know about contact lens hygiene, explained Prof Dart.
He said: ‘People will want to save money. So a student or a young person may try to cut corners to save money. They will get their eyes tested for lenses in the high street, but then get new supplies of lenses on the net.
‘They will decide to save money by avoiding contact lens checks. But these checks are vital, not just to see if the prescription needs changing, but to check eye health.
'You are putting a foreign object in your eye, and it is important your eyes are checked to make sure your contact lenses aren’t harming your eyes.’
Infection starts when contact lenses are exposed to the amoeba because, for example, the wearer stores them in water rather than sterile saline solution, or has worn them in the shower.
If spotted early it can be treated with drugs, but if left untreated the infection can badly scar the eye. In a third of cases the cornea is so badly scarred it needs to be taken out and replaced with a donor one.
Prof Dart has seen a seven-fold increase in cases of the infection – officially called Acanthamoeba Keratitis – at his Moorfields clinic since 2010, up from 11 a year to about 80.
Nationwide, the number of known cases has risen from around 100 to more than 200 a year, although Prof Dart believes that is just a fraction of the true number, as many people fail to seek treatment.
Optometrist Dr Nigel Best, from Specsavers, said the real threat came from ordering lenses online from foreign-based websites, rather than UK-based firms which required a prescription.
He explained: ‘Once the prescription expires, you cannot re-order online from a reputable UK website, so you have to go back for a test.
‘However, there are an awful lot of foreign websites [selling to UK customers] and these don’t require a prescription. Because they are based outside the UK, the General Optical Council is powerless to act.’
Art student Saira Hussain, 21, from Southend, Essex, developed the infection in her first year at university.
‘I used to do things that put you at risk like wearing throwaway daily contact lenses more than once and sleeping in them if I stayed over at a party. And I showered in them, but I didn’t know I was doing anything wrong,’ she said.
‘I developed a sore red eye and blurry vision and after a number of weeks ended up as an inpatient at Moorfields. My vision in one eye has been damaged. My other eye compensates, but it has been a shock.’
Other risky contact lens behaviour includes licking lenses to moisten them if they fall out, swimming in them, touching them with dirty hands, reusing solution, and even making a ‘DIY’ solution from tap water and salt.