Coating may make contact lenses safer

A NEW plastic coating could help make extended-wear contact lenses safer. The developers claim the coating will let people keep their lenses in for up to a week without having to remove them for cleaning.

The coating, developed by a small British company, is added on top of a conventional lens surface. It forms a chemical bond with the lens, and can be used on both hard and soft varieties.

The structure of the synthetic coating is irregular. It is in constant motion once immersed in the fluids of the eye, behaving rather like seaweed in an ocean current. This movement on the surface fools the eye into thinking the lens is living tissue, so avoiding the normal process of rejection, part of which is the build up of proteins seen on all contact lenses.

Daily-wear contact lenses must be cleaned regularly to keep this build up at bay, since it increases the risk of infection and can make lenses less effective. The structure of the new polymer also helps keep the eye healthy by letting oxygen pass through the lens in both directions.

The company that developed the coating, BioInteractions of Reading, has won two recent technology awards worth pounds 10,000 for its work, and is talking to contact lens manufacturers about developing the idea. A world-wide patent search has found no other similar inventions.

Dr Ajay Luthra, managing director of the company, said he hopes to explore the possibility of using the coating for other implants - such as heart valves and artificial blood vessels, and for surgical equipment such as catheters. The aim is to prevent blood clots forming around medical devices, which can put patients at risk. Leading transplant specialists have shown an interest.

Nigel Burnett Hodd, a former chairman of the Association of Optometrists and a contact lens specialist, welcomed the development but sounded a note of caution, saying he would want to see the results of full clinical trials before giving a conclusive response. 'We have seen a lot of claims about new materials for contact lenses, but many of these have proved unstable eventually.'

Contact lenses, particularly disposable varieties, are becoming more popular as the manufacturing process gets cheaper. Recently, the British Technology Group said it was backing a new process that produces lenses so cheaply that disposable versions worn for just one day, then thrown away, are now feasible.

But Mr Burnett Hodd said throwaway lenses can be of inferior quality because they are mass produced rather than being tailored to individual patients. He also pointed out that only a small percentage of contact lens wearers suffer problems because of protein deposits, and said the best solution to this was a rigorous cleaning regime.

He did not expect the new polymer to be available commercially for at least five years.