As a general description of the vision apparatus I have taken the one made by Testud in his compendium of anatomy:

“The vision apparatus is located between the anterior part of the skull base and the massif of the face, in a large cavity called the orbit. The set of organs that constitute it in topographic anatomy is called the orbital region. This region is one of the most important in the head. It includes, as we know, the eyeball and the optic nerve, and owes to the presence of these two organs, and more especially the eye, its anatomical, clinical and operative interest.

If we examine the orbital region in a sagittal section (Fig. 290), it is noted, from the first moment, that the eyeball is housed in a cavity with bony walls, the orbit. In the skeleton this cavity has no anterior wall; Instead, it has a wide orbit, the base of the orbit (Fig. 289), which is circumscribed by a bony line, very evident everywhere, the orbital rim. But in the living, covered with soft parts, the orbit orbit is closed, in part at least, by the eyelids, constituting the palpebral region. The eyelids, then, come to form the anterior or superficial wall of the orbital cavity. They are separated from the eyeball by a narrow, almost virtual cavity through which tears circulate: the conjunctival cavity.

Secondly, we will note that, in the aforementioned sagittal section, the eye is held in its position within the orbit by a membrane that, arranged frontally, is located behind it: the aponeurosis or Tenon's capsule.

Lastly, this section shows us that the eyeball only occupies the anterior half of the orbital cavity, its posterior half being occupied by adipose tissue and by muscles, veins and nerves destined for the eye. The two halves, anterior and posterior, are separated from each other by Tenon's aponeurosis, which, while constituting a means of support for the eye, is a septum that subdivides the orbital cavity into an anterior or precapsular segment and a posterior or retrocapsular segment. Later we will see that this division is not only comfortable for description, but also has real anatomical and surgical importance.