Tiny, glowing robots could soon be injected into the eye to alert doctors of low oxygen levels that can lead to blindness.

Led by Bradley Nelson, a professor of robotics and intelligent systems at ETH-Zurich, researchers created devices 1 millimeter in length and one third of a millimeter in width that, once injected, can be steered through the eye’s vitreous fluid via external magnetic fields.

Researchers coated the micro-robots with nanospheres made of a special dye that turn the devices into oxygen sensors. When exposed to a certain wavelength of light, the dye glows. Fluorescence that fades quickly indicates a high amount of oxygen surrounding the dye; slow fading indicates low amounts of oxygen.

While the miniature robots have been successfully tested to measure oxygen levels in water, the next step is to do tests on an eye. Researchers plan to inject the robots into the vitreous fluid and direct them towards the surface of the retina. Here a pulse of light would be applied and the robots’ fluorescence would be microscopically observed. To remove them, a needle would be re-inserted into the eye and the robots would be magnetically drawn to it.

The researchers have already created micro-robots that could deliver medicine or remove scar tissue from the eye, but their new oxygen-sensing robots indicate when blood flow to the eye is restricted, which can result in vision loss. Methods for gauging oxygen levels within the eye already exist, but ETH researchers claim they aren’t sensitive enough.