Tapetum Lucidum: 3D Eyeshine Ray Model

A full 3D ray-traced model of the real optics behind eyeshine: a draggable flashlight sends a chief ray into a schematic eye, where it is bent toward the optical axis by the lens, partially absorbed by the photoreceptor layer, reflected off the curved tapetum lucidum mirror using the true law of reflection, and traced back out through the eye. Because the tapetum is curved, the reflected ray only heads back toward the camera when the flashlight and the viewing angle are nearly aligned — real retroreflection, the mechanism behind why animal eyes glow in headlights but not diffuse room light.