People who regularly wear soft contact lenses are being warned that they are at greatly increased risk of a serious eye condition which can lead to blindness.
The infection, microbial keratitis, is extremely rare in non-lens wearers, affecting just one person in 30,000. But in recent years, doctors have seen a worrying increase in the number of young people and professionals who have fallen victim to it. Some have become partially or totally blind in the affected eye.
The latest study, published today in the Lancet medical journal, found that the type of contact lens people wear makes a big difference to their chances of being infected. Researchers led by Dr Kam Cheng from Rotterdam Eye Hospital studied 1.4million Dutch contact lens wearers. They identified all new cases of microbial keratitis during a three-month period in 1996, and matched these with the use of contact lenses. They found that the incidence of infection in people who wore rigid gas-permeable or hard lenses was low, at about 1.1 cases per 10,000 wearers per year. But for people who wore soft lenses the risk was much higher. It was 3.3 times higher for people who wore daytime lenses, and almost 20 times higher for whose who kept them in overnight.
Dr Cheng said: 'Use of contact lenses can lead to profound and permanent visual loss in otherwise healthy eyes. The main risk factor for corneal infection is overnight wear, which should be discouraged.' A ban on extended-wear soft lenses imposed on health grounds in the UK in 1990 has recently been lifted, following the introduction of disposable products made from new materials. In the European Union they are approved for up to 30 days extended wear.
John Dart, a consultant eye surgeon from Moorfields Eye Hospital, London, last night warned that the lifting of restrictions might be premature. He pointed out that, based on the Dutch research, 1,650 more cases of microbial keratitis might be expected each year if half of Britain's contact lens wearers switched to extended-wear lenses. 'This is a particularly devastating condition,' he added, 'and it may be prudent for people to cut the risk by not sleeping in their lenses overnight, and ensuring that they follow good hygiene in storing and cleaning their lenses.'