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A coating that mimics the body’s natural mechanism for killing bacteria could allow contact lenses to be worn constantly for several months at a time.

Researchers at the Texas Tech University Health Sciences Centre in Lubbock applied a thin coating of selenium to normal silicone hydrogel lenses and succeeded in preventing bacterial growth during long-term wear.

During use, bacteria can form around items within the eye. The longer lenses are worn, the greater the possibility of infection.

‘Some of these organisms can eat through the cornea in as little as a day,’ said project leader Dr Ted Reid. ‘Bacteria formation is the last major problem facing lens wearers.’

The coating, which is just one molecule thick, is formed by dipping a lens into a solution of an organo-selenium compound containing selenium and an amino group, before allowing it to set for a couple of minutes.

During the process, the organo-selenium forms a bond with carboxyl groups present on the surface of the lens, forming clusters with gaps in between that allow the lens to remain porous.

Selenium, a naturally occurring element found in soil, plants and some foods, then kills bacteria by forming superoxide radicals, exactly as the white blood cells of the body do when faced with disease.

The coating does not interfere with the prescription or colour of the lens, and tests have shown that the solution stays in place for at least two years.

In tests on rabbits, electron micrographs showed that the animals’ eyes remained healthy and free of bacteria after two consecutive months of wearing the lenses.Though the coating still requires government approval and may not be commercially available for up to two years, Reid is carrying out his own trial by wearing a pair of lenses himself and measuring their endurance before bacteria forms.

Experiments are also being carried out into the possible use of the coating to prevent secondary cataract formation, following the implanting of replacement plastic lenses after cataracts are removed.

However, Dan Ehrlich, senior optometrist at London’s Moorfields Eye Hospital was cautious about the findings.

‘This research seems to be at an extremely early stage and as such it would be very difficult to tell whether this technique could be used for contact lens wear at any point in the future,’ he said.

‘Further research will need to be carried out into the efficacy of selenium in killing bacteria and the other microbes that can adhere to the contact lens and pose a threat to the health of the eye.’