"Some radiation therapy patients report seeing flashes of light in front of their eyes during treatment – even when their eyes are closed. Now this long-standing mystery may have been solved, thanks to this weird effect being caught on camera for the first time," according to ScienceAlert.

"What's happening, according to a new study, is that enough light is being produced inside the eye to cause these visual sensations. It's what's known as Cherenkov emissions or Cherenkov radiation, the same effect that causes nuclear reactors to glow blue when they're underwater. ...

...The discovery could help to improve future radiation treatments – and to put patients' minds at ease about those flashing lights.

'Our newest data is exciting because for the first time, light emission from the eye of a patient undergoing radiotherapy was captured,' says biomedical engineer Irwin Tendler, from Dartmouth. 'This data is also the first instance of evidence directly supporting that there is enough light produced inside the eye to cause a visual sensation and that this light resembles Cherenkov emission.'"