One potential way round this is to use soft contact lenses steeped in a solution of drug that leach it into the eye. However, it is hard to cram a dose large enough to be clinically significant into lenses, which also tend to leak the drugs away too quickly. So Mark Byrne, a chemical engineer at Auburn University in Alabama, has a developed a contact-lens material that can hold much greater concentrations of drugs and release them more slowly.

The trick is to design the molecular structure of the lens material to mimic tissue-receptor sites that the drug will target within the body. The goal is to make the dummy receptors strike a balance, not holding the drug too tight, but also only releasing it slowly into the eye. Byrne has set up a company – OcuMedic – to commercialise the idea and is already developing anti-fungal contact lenses for treating eye infections in horses.