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Last Updated: Tuesday, 22 March, 2005, 01:39 GMT
Lenses 'could cut infection risk'
Woman inserting contact lens
Lens wearers should listen to their optician's advice
Sleeping in certain contact lenses reduces the risk of developing severe eye infections, eye experts have said.

Silicone hydrogel lens wearers have a five times lower risk of developing keratitis, researchers from the Royal Eye Hospital in Manchester estimate.

Contact lens wearers who attended A&E with infections were assessed for the British Journal of Ophthalmology study.

But a Moorfields Hospital expert said much larger studies were needed to confirm the findings.

There is no evidence of a higher risk compared to the older type of lens
John Dart, Moorfields Eye Hospital

Silicone hydrogel lenses available are CibaVision Focus Night and Day, Bausch and Lomb PureVision and Johnson & Johnson Acuvue.

Anyone who has been prescribed contact lenses and is told they can wear them at night will have been given one of these brands.

It was believed they should minimise infection risk because they transmit more oxygen through to the eye, but reports of some cases of infection among people wearing silicone hydrogel lenses had raised concerns.

In total, almost three million people wear contact lenses in the UK.

In the catchment area of the Royal Eye Hospital, there are 55,000 contact lens wearers, including 30,000 hydrogel lens wearers and 1,700 silicone hydrogel lens wearers.

Day and night

Over the year that the study took place, all contact lens wearers were asked to supply details of lens hygiene, type and pattern of wear, including whether they slept in them.

Four types of lenses were studied - rigid, hydrogel daily disposable, hydrogel and silicone hydrogel.

Eye specialists assessed the patient's condition by looking at damage to their cornea.

Thirty-eight, nine of whom slept in their lenses, were identified as having a severe infection.

Extrapolating out their findings, based on the incidence rate in the population served by the hospital, the researchers estimated rates of 96 cases of severe keratitis per 10,000 wearers a year for hydrogel lenses, compared with almost 20 per 10,000 wearers a year for silicone hydrogel lenses.

Dr Philip Morgan, who led the study, told the BBC News website: "Sleeping does increase the risk of developing eye infections. But silicone hydrogel lenses carry a much lower risk."

He added: "People do need to take the advice of their eye care practitioner and use their lenses as advised."

But John Dart, a consultant ophthalmologist at Moorfields Eye Hospital, said he had some concerns about the way the study had applied its findings to the whole contact lens-wearing population in the UK because there were different patterns of lens-wearing in each area.

He added: "There is a general problem with overnight contact lens- wearing, because there is very little tear turnover under lenses and bacteria can get under the lenses."

Mr Dart said he would like to see more robust research into the area to confirm that wearing silicone hydrogel lenses carried a lower risk of infection.

"But I have no problem with people being told to move to this newer type of lens because there is no evidence of a higher risk compared to the older type of lens."

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