1. Tapetum Lucidum: Tigers have a layer of tissue behind their retinas called the tapetum lucidum. It is composed of multiple layers of cells that contain reflective crystals, such as guanine.
2. Enhanced Light Reflection: When light enters a tiger's eye, some of it passes through the cornea, pupil, and lens, reaching the retina. The remaining light that doesn't get absorbed by the retinal cells is reflected back by the tapetum lucidum.
3. Eye Shine: The reflected light undergoes multiple internal reflections within the tapetum lucidum, maximizing the amount of light reaching the photoreceptor cells in the retina. This enhanced reflection increases the sensitivity of the tiger's eyes, allowing them to see better in low-light conditions.
4. Apparent Glow: The increased light returning from the tiger's eyes appears as a bright, glowing effect when viewed from the front in darkness or low-light conditions. This reflected light gives tigers excellent night vision and helps them hunt effectively in their nocturnal habitats.
So, while tigers' eyes seem to glow in the dark due to reflected light, it is specifically the tapetum lucidum that allows for enhanced light reflection and heightened visual sensitivity, rather than external light sources simply bouncing off their eyes.