Final answer:
The tapetum lucidum is the layer of cells that lie behind the retina, reflecting light to improve the visual acuity in nocturnal animals. It's this structure that causes 'eyeshine' in animals when light is shone into their eyes at night.
Step-by-step explanation:
The layer of cells that lie behind the retina and improve the visual acuity of nocturnal animals is called the tapetum lucidum. This structure reflects visible light that has already passed through the retina, increasing the light available to the photoreceptors and enhancing an animal's ability to see in low-light conditions. In many nocturnal animals, this reflective layer is what causes the characteristic 'eyeshine' when a light is shone into their eyes at night.
The retina is a layer of the eye containing cells sensitive to light (rods and cones), which allows the conversion of light into neural signals. The fovea is the part of the retina where visual acuity is the highest due to the absence of supporting cells and blood vessels, enabling less interference with light reaching the photoreceptors. Although humans do not have a tapetum lucidum, understanding its function in other animals helps us appreciate the adaptations that evolution has produced for survival in various environments.