Eye shine in nocturnal mammals is different from the red eye seen in some flash photographs. eye shine is the reflection of light off the tapetum lucidum. what visual mechanism might explain red eye ?

Red-eye effect on photographs happens because too much of the very bright light from the flash passes into the eye through the pupil (flash is too fast so the pupil wan disable to close). The camera records the light which is reflected from the interior of the eye (fundus) and got out through the pupil. The red colour is because of the plentiful amount of blood in the vascular layer of the eye (choroid).