The lower eyelid forms the lower part of the palpebral fissure and thus covers the lower part of the eyeball. It clings tightly to the eyeball and covers the lower edge of the iris. It is not as flexible as the upper eyelid and only plays a small part in closing the eye. Nowhere else in the body is the skin as thin as on the lower eyelid. A ring-shaped muscle is located right under this thin eyelid skin (the orbicularis oculi muscle). This muscle helps to close the eye. The eye socket is located under this muscle. The eyeball, the muscles that move the eyeball and the optic nerve are located in the eye socket. The eye socket is lined with fat to protect the soft eyeball in the bony orbital wall. So the fatty tissue cannot protrude from the eye socket, it is closed off from the eyelid behind a fine membrane (orbital septum). With aging, this membrane weakens and the fat can protrude from the eye socket. This is commonly referred to as an „eye bag“ or „tear sac“. It has nothing to do with tears, however, as the lachrymal gland is actually located in the upper outer part of the eye socket.