Overview of the Eye
The bony orbit is pyramidal in shape and is composed of 7 bones:
frontal, ethmoid, maxilla, lacrimal, zygomatic, palatine and sphenoid.
consists of 4 walls and an apex.
The medial walls are parallel and
separated by the ethmoid and sphenoid sinuses.
The roof of the orbit is
largely made of the orbital plate of the frontal bone.
It contains the
lacrimal fossa that contains the lacrimal gland laterally.
The lateral wall
consists of the zygomatic bone and greater wing of the sphenoid.
floor is largely composed of the orbital surface of the maxilla.
the infraorbital groove in which the infrorbital nerve (a branch of the
maxillary division of the trigeminal nerve, CN V) lies.
The floor separates
the bony orbit from the maxillary sinus.
The medial wall consists of the
orbital lamina of the ethmoid bone, the lacrimal bone, and the frontal
process of the maxilla.
The lacrimal bone contains the lacrimal fossa that
holds the lacrimal sac.
The ethmoid bone is very thin, separating the
ethmoid air cells and sphenoid sinus from the orbit.
The apex is formed
by the sphenoid bone and contains several openings:
1) the optic canal
contains the optic nerve and ophthalmic artery; 2) the superior orbital
fissure contains cranial nerves III, IV, V
, and VI, and superior ophthalmic
The inferior orbital fissure contains branches of the maxillary nerve
The eyelids contain 5 layers:
1) skin; 2) subcutaneous tissue; 3)
muscles; 4) tarsal plate and 5) conjunctiva.
The eyelids are composed of 3
orbicularis oculi, the sphincter muscle of the eyelid innervated
by the Facial nerve (CN VII); levator palpebrae superioris, innervated by
the Oculomotor nerve (CN III), and the superior tarsal muscle (Muller’s
muscle) innervated by the sympathetic branches from the superior cervical
The tarsal plate provides support to the eyelid.
It contains tarsal
glands (sebaceous glands).
Inflammation of the tarsal glands causes a
meibomian cyst (chalazion) or, when infected, an internal hordeolum.
difference between a chalazion and a hordeolum is that the chalazion is a
granuloma formed from extravasated lipid whereas, a hordeolum is an
acute suppurative infection usually caused by
orbital septum is composed of the superior and inferior palpebral fascia.
connects the tarsal plates with the periosteum of the orbit. It forms a
circumferential curtain that serves as a barrier to infection by separating
the superficial subcutaneous tissues from the deeper structures of the orbit.
The conjunctiva consists of two parts, palpebral and bulbar.
conjunctiva covers the inner surface of the eyelid, and the bulbar
conjunctiva covers the sclera, but not the cornea.
Ciliary glands (glands of
Zeiss and Moll) are found at the base of the eyelashes.
The glands of Zeis
are sebaceous glands which may become infected and produce an external
hordeolum (sty), or may develop a chalazion (non-infectious).