What is an eye crack?

The eyelid is located at the front of the orbit covering the surface of the eyeball, divided into upper eyelid and lower eyelid, the fissure between the upper and lower eyelids is called palpebral fissure. The height of palpebral fissure is about 8mm when normal elevation is made, and the upper eyelid generally covers the upper part of cornea 1-2mm when elevation is made. The part connecting the inner and outer canthus of the upper and lower eyelids is called inner canthus and outer canthus. The size and length of each palpebral fissure may vary slightly, which also constitutes the appearance characteristic. The eyelid fissure of both eyes is basically symmetrical in normal people. One eye is big and the other eye is small, which is called upper eyelid ptosis. Upper eyelid ptosis can also be manifested in both eyes at the same time, but the height of the eyelid fissure of both eyes may not be the same. Usually, the big eyes actually refer to the upper and lower eyelids to be wide, and the small eyes refer to the upper and lower eyelid fissure, that is, the eyelid fissure is short. If the upper and lower eyelids cannot be completely closed, it is called rabbit eyes, and the formation of rabbit eyes may be caused by nerve paralysis or excessive eyeball protrusion.