This is the dream of many: perfect vision without glasses. You wear lenses while sleeping and wake up with perfect vision throughout the day.

The technique, called Ortho-K (Orthokeratology), involves wearing special contact lenses while you sleep to fix the curvature of the eye.

"Ortho-K is similar to an orthodontist using a brace to straighten teeth. We take extremely accurate and detailed measurements of your eyes. We then have a pair of hard contact lenses made up with a curvature calculated to squeeze each eye gently in the right places to correct a range of short-sighted and astigmatic prescriptions." said Dr. David Thomas, an optician with over 30 years of experience from Cambridge.

People with myopia have too powerful eyes, focusing on light before it reaches the retina.

Ortho-K flattens the cornea, making it a less powerful lens. When the Ortho-K lenses are removed in the morning, the eye slowly turns back to its myopic state, but in 1-2 days and the lenses can even slow down the deterioration of vision, including in children.

"Ortho-K lenses are gas permeable, so oxygen can get through to keep eyes in good order. And wearing them at night cuts down the risk of getting dust between the contact lens and the eye, which can cause irritation with standard lenses."

The effects of Ortho-K, unlike those of laser surgery, are totally reversible.

Ortho-K is popular in the Netherlands, Switzerland, Germany, UK and the US and was originally developed by the Dutch company Procornea.

Chinese technique prescribes to myopia patients to sleep with small bags of sand on their eyes. As myopia is induced by the eyeball lengthening, the weight of the sandbags would flatten for a while the eye.

Ortho-K was first discovered 40 years ago, when researchers observed that some patients could see better after the removal of their contact lenses. These lenses are also ideal for contact sports and swimming, when standard lenses cannot be worn.