Overview_of_the_Eye

Overview_of_the_Eye - Overview of the Eye The bony orbit is...

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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. It 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. The floor is largely composed of the orbital surface of the maxilla. It contains 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 1 , and VI, and superior ophthalmic vein. The inferior orbital fissure contains branches of the maxillary nerve and vessels. The eyelids contain 5 layers: 1) skin; 2) subcutaneous tissue; 3) muscles; 4) tarsal plate and 5) conjunctiva. The eyelids are composed of 3 muscles: 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 ganglion. 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. The 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 Staphylococcus aureus . The orbital septum is composed of the superior and inferior palpebral fascia. It 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. The palpebral 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). The glands
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Overview_of_the_Eye - Overview of the Eye The bony orbit is...

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