Scientists have developed colour-changing contact lenses that can deliver drugs and monitor eye treatments.

Researchers from China Pharmaceutical University and Southeast University in China sought to create a drug-delivering contact lens that would change colour as the medication is released into the eye.

According to the study published in the journal ACS Applied Materials & Interfaces, the lens could control and indicate the sustained release of many ophthalmic drugs.

It is difficult to known how much medication is actually getting to the eye, when eye drops and ointments are administered.

This is because the eyes tend to reject foreign elements, and tears start rapidly start flowing when something goes into the eye.

While this process is usually helpful for avoiding infection and damage from foreign objects, it can hinder the uptake of much-needed medications.

Contact lenses may be a more effective way to deliver drugs directly to the eye, but real-time monitoring of drug release is still a challenge.

The researchers fabricated 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.

Then, the team exposed the lenses to a solution of artificial tears, which was used 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, researchers said. They could see this shift with the naked eye and with a fibre optic spectrometer.