Bones of the Orbital Region

Fetal Development and the Eye Structure

• The hyaloid canal connects the optic disc to the lens's posterior surface in fetuses, filled by the hyaloid artery which regresses before birth.
• The vitreous body slightly enhances the eye's magnification, supports the lens, and holds the retina against the pigmented layer.

The Lens

• The lens is transparent, biconvex, and encapsulated, located behind the iris and in front of the vitreous body.
• Comprised of an elastic capsule, anterior cuboidal epithelium, and lens fibers from the equatorial epithelium; these fibers form the lens's bulk.
• The lens capsule's tension causes a preference for a globular shape, essential for focusing.
• The lens equator connects to ciliary processes via the suspensory ligament, which influences its shape for distance vision.

Extraocular Muscles and Eye Movements

• Superior and inferior recti originate about 23° medial to insertions, enabling optimal elevation or depression of the cornea.
• Testing involves lateral eye movement to assess the actions of the recti and oblique muscles.
• Intrinsic muscles, including the ciliary muscle, constrictor, and dilator pupillae, do not move the eyeball but control pupil size.

Fascial Sheath of the Eyeball

• The fascial sheath surrounds the eyeball, separating it from orbital fat and allowing free movement.
• Medial and lateral check ligaments attach sheath for the medial and lateral recti to the orbital walls.

Bones of the Orbital Region

• Composed of frontal, zygomatic, maxillary, ethmoid, lacrimal, palatine, and sphenoid bones, forming a protective bony orbit.
• Extraocular muscles like the recti and obliques control eyeball movement within the orbit.

Functions of the Orbital Region

• Protects the eye, supports and moves the eyeball, controls light entry, and maintains lubrication.
• The inferior ophthalmic vein connects to the pterygoid venous plexus, facilitating drainage into the cavernous sinus.
• No lymph vessels or nodes are present within the orbital cavity.

Eye Movement Terminology

• Eye movements include elevation (upward), depression (downward), abduction (laterally), and adduction (medially).
• Six voluntary muscles: superior rectus, inferior rectus, medial rectus, lateral rectus, superior oblique, inferior oblique.

Iris and Pupil Functionality

• Sphincter pupillae receives parasympathetic innervation from the oculomotor nerve, controlling pupil constriction.
• Dilator pupillae responds to sympathetic fibers for pupil dilation under low light or stress.

Nervous Coat: Retina

• The retina includes an outer pigmented layer and an inner nervous layer, connecting with the choroid and vitreous body.
• The macula lutea, located in the retina's center, is crucial for sharp vision, while the ora serrata marks the retina's non-receptive anterior edge.