If you've ever tried using eye drops, then you'll know that a great deal of the medication simply ends up being flushed from your eye by flowing tears, in a process that naturally keeps foreign objects out. Drug-dispensing contact lenses are an alternative, with an experimental new one changing color to verify that it's done its job.

The prototype dye-free lens was made via a process known as molecular imprinting – this involves creating tiny cavities within a material that match the size and shape of the molecules of a specific compound. In this case, the material was a polymer, and the compound was timolol, which is a drug that's used to treat glaucoma.

After those cavities were "loaded" with the drug, the lens (pictured above, in a flask) was subjected to a solution of artificial tears, simulating conditions in the eye. As the timolol was gradually released, the structure of the cavities became altered, causing the iris area of the lens to turn blue. This color-change was visible to the naked eye, and could be quantified using a fiber optic spectrometer.

It is now hoped that one day such contact lenses could be loaded with other medications to treat a variety of conditions. The research, which is being led by China Pharmaceutical University's Dawei Deng and Southeast University (China)'s Zhouying Xie, is described in a paper that was recently published in the journal ACS Applied Materials and Interfaces.

As a side note, scientists at Canada's Western University have previously created contacts that change color to indicate when their wearer's blood glucose levels change.

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