London: Here's a word of caution for those who wear contacts -- going to sleep in your lenses can blind you, experts have warned.

According to them, people should make it a point to take out and rinse contact lenses as poor lens hygiene can lead to a range of nasty eye ailments, including microbial keratitis, an infection of the cornea, the clear frontal part of the eye where lenses sit.

Left untreated, it can lead to permanent visual damage and, in extreme cases, blindness, they have warned.

The eye has natural protection against the foreign bodies through a fluid covering the eye that contains protective enzymes and by blinking, which prevents anything sticking to the eye's surface.

Yet minute air and waterborne microbes sometimes break through these defences, penetrating the protective layer of cells on the cornea.

The bacteria pseudomonas is the most common keratitis-causing microbe, while the most dangerous is acanthamoeba, a single-cell organism found in tap water, particularly in hard- water areas, which breeds in dirty lens case, say the experts.

"Pseudomonas and acanthamoeba occur naturally in the environment, but particularly in bathrooms. Rinsing or storing your lenses in tap water really can get you in lot of trouble.

"In fact, bathrooms are not the best places to put in your contact lenses at all. And you should always use sterile lens-cleaning solution," Dr Simon Kilvington, a microbiologist from the University of Leicester was quoted as saying.

Reusing lens cases for more than a month is also dangerous, he added. Parwez Hossain, a senior lecturer in ophthalmology at the
University of Southampton eye unit, says significant numbers of cases could be avoided if people took the time to clean and store their lenses properly.

"Contact lenses are one of the leading causes of corneal infections, most stemming from abuse of the way they should be cared for.

"Wearers may not feel all the features of early infection. The pain will start as the infection takes hold, generally getting worse once the lens, which was affording some protection, is taken out.

"Leave it out for a day or two and sensation returns to the cornea then it really begins to hurt," he added.

Even a Dutch study in 1999 found that soft-lens wearers were three times more likely to get microbial keratitis than those who wore rigid gas-permeable lenses. And people who left their lenses in overnight were almost 20 times more likely to develop the condition.

(Agencies)