In this section we'll look at the eye and its surroundings. We've already seen the nerves of the orbital region in part 3 of this tape. In this section we'll first look at the bony features of the orbital cavity, then we'll look at the eye itself, then at the eye muscles, and lastly the eyelids and lacrimal apparatus.
Let's start with the bones. This is the bony orbit, or orbital cavity. It's described as having a roof, a floor, a medial wall, and a lateral wall. The rim of the orbit, is called the orbital margin. It's thick and clearly defined above, laterally , and below. Here medially the orbital margin is less distinct: the medial wall of the orbit blends with the countours of the nose and the central part of the forehead.
The orbital margin curves distincly backwards, both above, and below. Because of this the orbital margin is much further back laterally, than it is medially.
01.27This reflects an imortant fact about the orbital cavity: it doesn't face directly forwards. We can see this best in a skull in which the roof of the orbit has been removed. This lets us look down into the orbit from above.
The medial wall of the orbit faces directly forward, but the lateral wall is angled outward by about 45°, so that the center line of the orbit is a little over 20° off the mid-line.
As we saw in tape 4, several bones are involved in forming the orbit. Starting medially this is part of the ethmoid bone, this is the underside of the frontal bone, this is the zygomatic bone, this is part of the maxilla, so is this, and this is the lacrimal bone.
Back here are the greater, and lesser wings of the sphenoid bone. Here at the narrow apex of the orbit are the optic canal and the superior orbital fissure.
The optic canal transmits the optic nerve and ophthalmic artery; the superior orbital fissure transmits the other nerves that enter the orbit and the superior orbital vein. In the living body the inferior orbital fissure, which forms an apparent gap between the floor and the lateral walls is bridged over with fibrous tissue.
This groove, the lacrimal groove leads downwards into the opening for the naso-lacrimal duct, which takes tears to the nasal cavity. The rim of the lacrimal groove is formed by the posterior lacrimal crest behind, and the anterior lacrimal crest in front.
The medial palpebral ligament is attached here, the lateral one here. The palpebral ligaments hold many of the anterior structures of the orbit in place.