Scientists have developed a drug-delivering contact lens (CL) that changes colour as medicines are released to help eye doctors and patients see whether eye medications are being delivered accurately.

A study in ACS Applied Materials & Interfaces says Chinese researchers Dawei Deng and Zhouying Xie made a colour-sensitive contact lens using molecular imprinting, a technique that creates molecular cavities in a polymer structure that match the size and shape of a specific compound, such as a medicine.

In laboratory experiments, the molecularly-imprinted contact lenses were loaded with timolol, a drug used to treat glaucoma. The team exposed the lenses to a solution of artificial tears, as a stand-in for the eye. As the drug was released from the contacts, the architecture of the molecules near the drug changed, which also changed the colour in the iris area of the lenses. No dye was involved in the process, reducing possible side effects, and the researchers could see this shift with the naked eye and with a fiber optic spectrometer. They say this new lens could control and indicate the sustained release of many ophthalmic drugs.