By Michael Hutton 

Sleeping in contact lenses  has generally been discouraged by eyecare professionals because of the long-held view that the risks of bacterial infection are greater when less oxygen can reach the cornea as is normally the case when people go to bed with their lenses in. However, the new overnight ortho-k or OK lenses for correcting short-sightedness are specially designed to be worn while sleeping and are manufactured from a base material with very high oxygen permeability. Under the slight pressure of the closed eyelids during sleep, the custom-designed ortho-k lenses gently flatten the surface of the eye to ensure that light enters at the correct angle and focuses directly on the retina rather than in front of it.

When the lenses are removed in the morning, the wearer enjoys perfect natural vision all day long until reinserting the lenses at night. More importantly, given that lens wear is only for the duration of a night's sleep - that is six to eight hours - sleeping in contact lenses  when they are ortho-k designs which allow high oxygen transmission means that infection risks become negligible. This compares with the problems traditionally associated with older hydrogel contact lenses which various clinical studies identified as being higher risk if not removed at night. Even with the newer silicon hydrogel contact lenses which have greater oxygen permeability, a perception remains that sleeping in them gives rise to increased infection risk.

This perception probably explains why extended wear contact lenses - designed to be worn for between two and four weeks without removal - have declined in popularity despite the introduction of silicon hydrogel technology. A recent study in Optometry and Vision Science highlighted that extended wear contact lenses now represent less than 8 per cent of the total world contact lens market, a reduction of one-third from the peak of 12 per cent in 2006. However, a further issue about extended wear lenses is the fact that they effectively stop the cornea from being exposed to the air for lengthy periods which is inconsistent with optimal eye health. By contrast, sleeping in contact lenses  which are ortho-k designs is not an issue since the eyes are fully exposed to fresh air after removal each morning.

Check if you are suitable for overnight ortho-k corrective contact lenses .