The Orbit Flashcards
Bones of the Orbit
Lacrimal, frontal, maxillary, palatine, zygomatic, ethmoid, sphenoid
Bounds of the orbit
Four walls: Superior wall, medial wall, floor (inferior wall), lateral wall. Apex and base
Superior wall of the Orbit
Almost horizontal. Also known as the roof; formed by the orbital part of the frontal (mainly) and sphenoid bones (lesser wings). Separates the orbit from the overlying anterior cranial fossa. Lacrimal fossa located in this region
Lacrimal fossa
located in the superolateral part of the orbital plate of frontal bone. The lacrimal gland is located here
Medial Wall of the orbit
Paper thin. Formed by the ethmoid (mainly), frontal, lacrimal and sphenoid bones. Contains the fossa for the lacrimal sac and nasolacrimal duct. Medial walls of the two orbits are parallel to each other. Anteriorly indented by the lacrimal groove and the fossa for lacrimal sac.
Floor of the orbit
Aka inferior wall. Formed by the maxilla (mainly), zygomatic and palatine bones Maxillary sinus is on the other side of the floor.
Lateral wall of the orbit
Thickest and strongest wall. Formed by the maxilla (mainly), zygomatic and palatine bones. Maxillary sinus is on the other side of the floor
Apex of the orbit
Located at the optic canal in the lesser wing of the sphenoid bone
Fracturing of orbits
Medial and inferior wall (floor) of orbit are very thin. Blowout fractures can result from indirect traumatic injury. All walls are thin and readily penetrated by a sharp object. Orbital margins usually remain intact
Orbital Tumors
Tumors might be located in the sinuses along the medial wall but can push into the orbit, pressing against the optic nerve. Tumors and bleeding can lead to protrusion of the eyeball: exophthalmos
Exophthalmos
Protrusion of the eyeball(s); can be resultant of orbital tumors and/or bleeding
Eyelids
Covered externally by skin and internally by conjunctiva (mucus membrane)
Tarsal Plates
Superior and inferior. connective tissue plates – form the skeleton of the lids
Tarsal Glands
embedded in the tarsal plates - secrete lipid material to lubricate edges of the lids
Ciliary Glands
large sebaceous glands of the eyelid
Orbicularis Oculi Palpebral Muscle
Innervated by facial nerve. Closes the eyelid.
Levator Palpebrae Superioris
Innervated by oculomotor nerve. Elevates the upper eyelid
Medial Palpebral Ligament
Origin and insertion of the orbicularis oculi muscle. Connects tarsal plates to medial margin of the orbit
Lacrimal apparatus
Orbital structures responsible for tear production and drainage. Consists of lacrimal gland, lacrimal ducts, lacrimal lake, lacrimal canaliculi, lacrimal sac, and nasolacrimal duct
Lacrimal gland and lacrimal ducts
Secrete the lacrimal fluid. Located in the superolateral part of the orbit (lacrimal fossa). Ducts 8-12 open in the superior conjunctival fornix. Lacrimal gland is stimulated by parasympathetic nerves of CNVII (Facial).
Lacrimal Lake
Collecting area of tears at the medial angle of the eye
Lacrimal Canaliculi
One for each eyelid. The lateral opening of the canaliculi are represented by the lacrimal papillae. Conveys tears from the lacrimal lake to the lacrimal sac
Lacrimal Sac
Dilated upper end of the nasolacrimal duct. The other end of the canaliculi opens here.
Nasolacrimal duct
Extends inferiorly into the nose. Opens at the inferior meatus of the nasal cavity
Conjunctiva
Line the inside of the eyelide, cover the sclera (white portion of the eye). Inside covering of the eyelid (palpebral conjunctiva) and eyeball (bulbar conjunctiva).
Palpebral Conjunctiva
Inside covering of the eyelid
Bulbar conjunctiva
Outer covering of the eyeball
Conjunctival fornix
Forms the junction between the bulbar and palpebral conjunctivas. It is loose and flexible, allowing the free movement of the lids and eyeball
Superior conjunctival fornix
the space in the fold of the conjunctiva created by the reflection of the conjunctiva covering the eyeball and the lining of the upper lid
Inferior conjunctival fornix
the space in the fold of conjunctiva created by the reflection of the conjunctiva covering the eyeball and the lining of the lower eyelid
Extraocular muscles
AKA Extrinsic muscles. Move the superior eyelid and the eyeball. Recti muscles (Superior, inferior, medial, lateral), superior oblique, inferior oblique, levator palpebrae superioris.
Describe the innervation of the extraoccular muscles
SO(IV) LR (IV). Rest (III). Superior Oblique CN IV (Trochlear), Lateral Rectus CNVI (Abducens), Rest CNIII (Oculomotor)
Recti muscles
Originate from the common tendinous ring- fibrous structure originating from optic foramen and part of the superior orbital fissure. All four recti muscles attach to the sclera of the eyeball. Recti: lateral rectus(CNVI), medial rectus, superior rectus, inferior rectus
Superior rectus
CNIII. Rotate pupils superiorly and medially
Inferior rectus
CNIII. Rotate pupils inferiorly and medially
Medial Rectus
CNIII. Rotate pupils medially
Lateral Rectus
CNVI. Rotate pupils laterally.
Nerves of the orbit
Optic Nerve, Opthalmic of CNV (CNV1), Oculomotor Nerve, Trochlear Nerve, Abducens Nerve, Autonomics
Optic Nerve
Enters orbit via optic canal
Opthalmic division of CNV
CNV1. First three terminal branches of opthalmic nerve enter orbit via superior orbital fissure. Supply sensory innervation to anterior orbit (lacrimal gland and eyelids), face, and scalp. Gives rise to frontal, lacrimal, and nasocilliary nerves.
Frontal branch of CNV1
Largest branch of CNV1. Located superficial to levator palpebrae superioris muscle along roof of orbit. Travels anteriorly to give rise to two branches: supraorbital and supratrochlear
Lacrimal Nerve
Smallest branch of CNV1. Enters the orbit through the superior orbital fissure and travels laterally superficial to lateral rectus muscle to reach lacrimal gland. Sensory nerve to lacrimal gland.
Nasocillary Nerve
Supplies sensory branches to the eyeball via ciliary nerves. Some of the ciliary nerves pass through the ciliary ganglion. Nasociliary nerve continues along the medial wall of the orbit and gives rise to the following branches: Posterior ethmoidal, anterior ethmoidal, infratrochlear (terminal branch, sensory)
Oculomotor Nerve
Enters through superior orbital fissure. Motor nerve to all muscles of orbit except Suprior Oblique (Trochler) and Lateral Rectus (Abducens).
Trochlear Nerve
Enters orbit through superior orbital fissure. Motor nerve to superior oblique muscle.
Abducens nerve
Enters orbit through superior orbital fissure. Motor nerve to lateral rectus muscle.
Parasympathetic Autonomic Innervation of the Orbit
Preganglionic parasympathetic fibers for the smooth muscles of the eyeball (not the lacrimal gland) originate from the brainstem and enter the oculomotor nerve. Oculomotor nerve carries these preganglionic fibers into the orbit. Inside the orbit all preganglionic parasympathetic fibers leave CN III via its motor root. Motor root is a branch of CNIII: carries preganglionic fibers to the cilliary ganglion (Located in the orbit along the posterolateral side of the optic nerve). postganglionic fibers leave the ganglion via the short ciliary nerves (branches of CNV) and enter the eyeball. In the eyeball, the parasympathetic fibers supply the smooth muscles of the eyeball
Cilliary Ganglia
Very small (size of pinhead). Contains cell bodies of postganglionic parasympathetic neurons; This is where the preganglionic fibers terminate and the postganglionic fibers begin
Parasympathetic Autonomic Innervation of Lacrimal Gland
Branches of CNVII. Postganglionic fibers originate from the pterygopalatine ganglion and enter the orbit via the zygomatic branch of the maxillary nerve
Sympathetic Innervation of the Orbit
Postganglionic sympathetic fibers from the superior cervical ganglion enter the orbit with the wall of blood vessels
Blood vessels of Orbit
Opthalamic artery and veins
Opthalamic artery
Enters the orbit through the optic canal and gives rise to the following branches: Supraorbital artery, supratrochlear artery, lacrimal artery, and central artery of retina
Opthalamic veins
Venous drainage occurs via superior and inferior opthalamic veins. These veins pass through the superior orbital fissure and enter the cavernous sinus inside the skull
