Final answer:
The opening between the eyelids is called the palpebral fissure, which varies in size but averages about 24-30mm in width and about 10mm in height. It is crucial for vision and eye health and is supported by the orbit.
Step-by-step explanation:
The opening between the eyelids is called the palpebral fissure. The normal opening for this space can vary among individuals; however, the average width is about 24-30mm and the vertical height is typically about 10mm. The palpebral fissure allows light to enter the eye and facilitates the range of vision. The eye's anatomy, including the palpebral fissure, is protected and supported by the orbit, which is the bony socket containing not only the eye but also the muscles that facilitate eye movement and lid elevation.
The medial and lateral angles (canthi) mark the corners of the palpebral fissure, with the lacrimal punctum located at the medial angle for tear drainage. Functioning together with other parts of the eye such as the conjunctiva and lacrimal gland, the palpebral fissure and associated structures are crucial for maintaining eye health and vision.