reflection of light from the inner surface of an eye through the pupil so that the eye has a luminous appearance (as in a cat)
At the edge of the road, the eyeshine of deer flashed in our headlights.
About the Word:
It's easy to see how eyeshine got that name, but how does it work? Eyeshine is an effect of the tapetum lucidum ("bright tapestry," in Latin), a layer of tissue found immediately behind or sometimes within the retina. It's this tissue that reflects visible light back through the retina. Despite what horror movies may suggest, humans do not have eyeshine.