Find these structures:
Ethmoid
Perpendicular plate
Cribriform plate
Crista galli
Orbital plate
Middle nasal concha
Superior nasal concha
Anterior ethmoidal foramen
Posterior ethmoidal foramen
Lacrimal
Lacrimal groove
Posterior lacrimal crest
Frontal
Lacrimal fossa
Trochlear fovea
Zygomatic
Orbital surface
Maxilla
Lacrimal groove
Sphenoid
Optic canal
Superior orbital fissure
Inferior orbital fissure
Find these structures:
Orbicularis oculi m.
Palpebral part
Orbital part
Palpebral fissure
Lateral angle (canthus) of eye
Medial angle (canthus) of eye
Conjunctiva
Palpebral conjunctiva
Bulbar conjunctiva
Conjunctival sac
Superior conjunctival fornix
Inferior conjunctival fornix
Fibrous layer of eyeball
Sclera
Cornea
Vascular layer of eyeball
Iris
Pupil
Lacrimal apparatus
Lacrimal gland
Lacrimal canaliculi
Lacrimal papilla
Lacrimal puncta
Lacrimal sac
Lacrimal lake
Lacrimal caruncle
Nasolacrimal duct
Note: The orbicularis oculi m. is a sphincteric, circumferential muscle of three parts (orbital, palpebral, and lacrimal), surrounding the orbit. The orbital part encircles the palpebral part. The palpebral part is typically involuntarily controlled (blinking), whereas the orbital part is typically voluntarily controlled (shutting the eyes tightly). The lacrimal part connects the posterior crest of the lacrimal bone and lacrimal sac to medial aspects of the tarsal plates of upper and lower eyelids. The orbicularis oculi m. is innervated by temporal and zygomatic brs. of the facial n. (CN VII).
Note: The palpebral fissure is the opening between the eyelids (palpebrae). The margins of the palpebral fissure are the medial and lateral angles (canthi). The medial angle is the more significant of the two angles due to the lacrimal system.
Note: The conjunctiva is a delicate mucous membrane that lines the eyelids and covers the anterior aspect of the eyeball (excepting the cornea and pupil). The bulbar conjunctiva covers the eyeball, and the palpebral conjunctiva lines the eyelids. The conjunctival fornices (superior and inferior) are the reflections of conjunctiva from bulbar to palpebral conjunctiva, and the conjunctival sac is the potential space between bulbar and palpebral conjunctiva.
Note: The fibrous layer of the eye is important in providing structure and strength to the eyeball. The two main structures include the sclera and cornea. The sclera covers the majority of the eyeball, is often referred to as the “white of the eye,” and is the insertion site for extra-ocular and intrinsic eye muscles. The cornea covers the anterior portion of the eye (approximately ⅙th of the anterior eye - Moore et al., 7th edition), is completely avascular, and sensitive to touch.
Note: The vascular layer of the eye (uvea) is composed of 3 structures: choroid, ciliary body, and iris. The iris is a diaphragm located on the anterior surface of the lens. The pupil, an aperture important in transmitting light, is located centrally in the iris. The iris is can appear various colors, while the pupil is black. The pupil is controlled by two muscles: sphincter pupillae (contracts pupil, parasympathetically-controlled) and dilator pupillae (dilates pupil, sympathetically-controlled).
Note: The lacrimal system begins with the lacrimal gland, located in the superolateral margin of the orbit. The lacrimal gland rests in the lacrimal fossa of the frontal bone, and sits between the aponeurosis for levator palpebrae superioris m. (medial to the gland) and the lateral rectus m. (inferior to the gland). The lacrimal gland secretes into the conjunctival sac along the lateral margin of the superior fornix. Tear fluid is conducted across the conjunctiva and accumulates in the lacrimal lake in the medial canthus. Deep to the lacrimal lake is a mound of skin, the lacrimal caruncle. Superior and inferior to the lacrimal lake are lacrimal papillae, which host small lacrimal puncta (pores) into which tear fluid flows. Fluid is conducted from the puncta via superior and inferior canaliculi into the lacrimal sac, the superior dilation of the nasolacrimal duct. The lacrimal sac lies in the lacrimal groove of the lacrimal bone. The nasolacrimal duct conducts tear fluid into the inferior nasal meatus.
Note: Route of lacrimal fluid: lacrimal gland → conjunctival sac → lacrimal lake → lacrimal papillae → lacrimal puncta → lacrimal canaliculi (superior & inferior) → lacrimal sac → nasolacrimal duct → inferior nasal meatus
Find these structures:
Lateral palpebral ligament
Medial palpebral ligament
Tarso-fascial layer of eyelids
Orbital septum
Superior tarsus (tarsal plate)
Inferior tarsus (tarsal plate)
Tarsal glands
Extra-ocular muscle
Levator palpebrae superioris m.
Superior tarsal m.
Note: The eyelids, layered from superficial-to-deep, include: skin, subcutaneous tissue, palpebral fibers of orbicularis oculi m. and associated connective tissues, a tarso-fascial layer, and palpebral conjunctiva (which rests upon the orbital conjunctiva of the eye). The edge of the eyelids host eyelashes and associated glands.
Note: The tarso-fascial layer of the eye consists of: tarsal plates, associated (tarsal) glands & ligaments, the orbital septum, and the insertion for the levator palpebrae superioris m. on the superior tarsal plate. The medial and lateral palpebral ligaments attach the upper and lower eyelids to the medial and lateral margins of the orbit.
Note: The levator palpebrae superioris m. attaches the apex of the orbit to the superior tarsal plate and tarso-fascial layer of the eyelid. Innervated by the oculomotor n. (CN III), when active, the muscle elevates the upper eyelid to open the eye. The levator palpebrae superioris m. is supplied by the ophthalmic a.
Note: A small layer of smooth muscle, the superior tarsal m., is located deep to the levator palpebrae superioris m. and inserts on the superior tarsal plate. Sympathetic fibers derived from perivascular plexuses of the ICA are typically transmitted to the superior tarsal mm. by the oculomotor n. (CN III).
Find these structures:
Cavernous sinus
Internal carotid a.
Cranial nerves
Optic n. (CN II)
Oculomotor n. (CN III)
Trochlear n. (CN IV)
Trigeminal n. (CN V)
Ophthalmic n. (V1)
Maxillary n. (V2)
Mandibular n. (V3)
Abducens n. (CN VI)
Note: The cavernous sinuses are relatively expansive dural venous sinuses lateral to the sella turcica, extending between the superior orbital fissures (anteriorly) and the apices of the petrous part of the temporal bones (posteriorly). Tributaries of these sinuses include ophthalmic vv., sphenoparietal sinuses, and superficial middle cerebral vv. The cavernous sinuses drain into the petrosal sinuses. Structures traversing the cavernous sinus include: the internal carotid a., abducens n. (CN VI), and internal carotid plexus of sympathetic nn. The oculomotor (CN III), trochlear (CN IV), and the ophthalmic (V1) and maxillary (V2) divisions of the trigeminal n. (CN V) are located in the lateral walls (meningeal layer of dura mater) of the cavernous sinuses. Cavernous sinus thromboses may endanger these structures.
Find these structures:
Nerves:
Optic n. (II)
Oculomotor n. (CN III)
Superior branch
Inferior branch
Branch to ciliary ganglion
Ciliary ganglion
Short ciliary nn.
Trochlear n. (CN IV)
Ophthalmic n. (V1)
Lacrimal n.
Communicating br. with zygomatic n.
Frontal n.
Supra-orbital n.
Lateral branch
Medial branch
Supratrochlear n.
Nasociliary n.
Long ciliary nn.
Posterior ethmoidal n.
Anterior ethmoidal n.
External nasal n.
Infratrochlear n.
Abducens n. (CN VI)
Muscles
Levator palpebrae superioris m.
Common anular tendon (common tendinous ring)
Superior rectus m.
Inferior rectus m.
Medial rectus m.
Lateral rectus m.
Superior oblique m.
Trochlea
Vasculature
Ophthalmic a.
Central retinal a.
Posterior ethmoidal a.
Anterior ethmoidal a.
Superior ophthalmic v.
Inferior ophthalmic v.
Note: The frontal nerve is the largest branch of V1. It afferently serves the medial upper eyelid (skin & conjunctiva), skin of the forehead, and frontal sinus mucosa. A prominent feature of the superior orbit, the frontal n. may be found superior to the levator palpebrae superioris m.
Note: The frontal n. divides about midway through the orbit into the supra-orbital (lateral) and supratrochlear (medial) nn. The supratrochlear n. passes superior to the trochlea of the superior oblique m. to afferently serve the skin of the medial forehead, and skin and conjunctiva of the medial superior eye. The supra-orbital n. further divides into medial and lateral branches, which afferently serve the mucosa of the frontal sinus, skin of the lateral forehead, and skin and conjunctiva of the lateral superior eye. Branches of the supra-orbital n. may be seen exiting the cranium via the supra-orbital foramen or notch.
Note: The levator palpebrae superioris m. attaches the apex of the orbit to the superior tarsal plate and tarso-fascial layer of the eyelid. Innervated by the superior division of oculomotor n. (CN III), when active, the muscle elevates the upper eyelid to open the eye. The levator palpebrae superioris m. is supplied by the ophthalmic a.
Note: The superior oblique m. originates on the sphenoid bone at the apex of the orbit, above the origin of the superior rectus m. The body of the superior oblique m. is one of the most superomedial structures in the orbit. The distal tendon of the superior oblique m. runs through the trochlea, a fibrocartilaginous loop (pulley) that attaches to the trochlear fossa of the frontal bone, before inserting on the posterosuperior sclera of the eye. This muscle is innervated by the trochlear n. (CN IV), and plays a role in abduction, depression, and intorsion (medial rotation) of the eye.
Note: The trochlear n. (CN IV) is the smallest cranial nerve and the only nerve to arise from the dorsal aspect of the brainstem. The trochlear n. travels within the lateral wall of the cavernous sinus, enters the orbit through the superior orbital fissure, and travels along the medial wall of the orbit to innervate the superior oblique m. This nerve is generally easiest to locate running deep to the posterior-most aspect of the superior oblique m.
Note: The lacrimal n. (V1) is the smallest branch of the frontal n. The lacrimal n. enters the orbit through the superior orbital fissure, and may be found superior to the lateral rectus m., en route to the lacrimal gland.
Note: Anatomists have classically understood (and taught) that the secretomotor postganglionic fibers to the lacrimal gland were conducted by the lacrimal n. from fibers transmitted from the pterygopalatine ganglion via the zygomaticotemporal brs. (i.e. pterygopalatine ganglion → zygomaticotemporal brs. → lacrimal n. → lacrimal gland). Recent studies show considerable variation in the course of these fibers, with the majority of cases demonstrating secretomotor postganglionic fibers from the pterygopalatine ganglion directly innervating the lacrimal gland via the zygomaticotemporal brs. Variants do exist that reflect the ‘classical condition.’
Note: The superior rectus m., like the other rectus muscles, originates from the common anular tendon (common tendinous ring), and inserts on the sclera of the superior eye. The common anular tendon surrounds the optic n. (CN II), oculomotor n. (CN III), and abducens n. (CN VI). The superior rectus m. is innervated by the superior division of the oculomotor n. (CN III). The superior rectus m. elevates and adducts the eye. The superior rectus m. also produces intorsion of the eye.
Note: The orbit is not a symmetric cone, nor does the eye gaze perfectly outward from the apex of the cone. As such, extra-ocular mm. may exert additional, rotational forces upon the eye. As an example, the superior rectus m. both elevates and adducts the eye. This adduction demonstrates such a rotational force.
Note: The lateral rectus m. originates from the common anular tendon, and inserts on the sclera of the lateral eye. The lateral rectus m. is innervated by the abducens n. (CN VI). The lateral rectus m. abducts the eye.
Note: The abducens n. (CN VI) arises from the brainstem, travels through the cavernous sinus, and enters the orbit through the superior orbital fissure (and also through the common anular tendon). The abducens n. innervates the lateral rectus m. (i.e. the ABDUCens ABDUCts the eye).
Note: The medial rectus m. originates from the common anular tendon, and inserts on the sclera of the medial eye. The medial rectus m. is innervated by the inferior division of the oculomotor n. (CN III). The medial rectus m. adducts the eye.
Note: The ophthalmic a. branches from the internal carotid a. after the ICA emerges from the cavernous sinus. The ophthalmic a. enters the orbit through the optic canal and branches to supply the structures of the orbit. The bulk of the ophthalmic a. may be found between the superior oblique m. and the medial rectus m., along the medial border of the orbit, and the many smaller branches typically accompany their namesake V1 branches (e.g. lacrimal, ant./post. ethmoidal, supra-orbital, supratrochlear, etc.). The ophthalmic a. gives rise to the central artery of the retina, which is bundled with the optic n. (CN II).
Note: The superior ophthalmic v. drains blood from the eye, superior orbit, ethmoidal cells, forehead, and the angular v. of the face. The inferior ophthalmic v. collects blood from the face and inferior orbit. Both the superior and inferior ophthalmic vv. may be valveless (there are instances of these vv. having valves), and may transport blood from the face to the cavernous sinus.
Note: The nasociliary n. branches from V1 in the superior orbital fissure. The nasociliary n. gives rise to:
long ciliary nn.,
anterior & posterior ethmoidal nn.,
infratrochlear n., and
a communicating branch to the ciliary ganglion transmitting afferent fibers from the eye via short ciliary nn.
Note: The long ciliary nerves arise from the nasociliary n. (V1) in the vicinity of the optic n. (CN II). These branches carry afferent fibers from the eye and postganglionic sympathetic fibers to the dilator pupillae muscle of the eye.
Note: The anterior and posterior ethmoidal nn. exit through the anterior and posterior ethmoidal foramina, respectively.
Note: The infratrochlear n. provides sensory innervation to conjunctiva, skin of eyelids, lacrimal caruncle and sac, and side of nose. This nerve can be seen exiting the orbit below the trochlea of the superior oblique m.
Note: Optic n. (CN II) travels through the optic canal to enter the orbit and pierce the sclera. This is the most obvious structure in this area. This cranial nerve is special somatic afferent and functions in vision.
Note: The ciliary ganglion is a peripheral parasympathetic ganglion for intra-ocular muscles, typically located on the lateral aspect of the optic n. (CN II) near the apex of the orbit. The ciliary ganglion has three conduits to/from the remainder of the PNS:
nasociliary n. (of V1) - transmits afferent fibers from the eye through the ganglion to the nasociliary n.,
oculomotor n. (CN III) - transmits preganglionic parasympathetic fibers to the ciliary ganglion, and
sympathetic - postganglionic sympathetic fibers are transmitted to (and through) the ciliary ganglion from perivascular plexuses of the internal carotid a. These fibers may also associate with the oculomotor n.
The ciliary ganglion communicates with the eye via the short ciliary nn.
Note: The short ciliary nn. transmit three types of fibers between the eye and the ciliary ganglion:
afferent fibers from the eye, through the ganglion, to the nasociliary n. (V1),
postganglionic parasympathetic fibers from the ganglion (preganglionics from oculomotor) to the ciliary muscles and sphincter pupillae muscles, and
postganglionic sympathetic fibers (from perivascular plexuses) to the intra-ocular vessels.
Note: The oculomotor n. (CN III) arises from the midbrain, travels within the lateral wall of the cavernous sinus, divides into superior and inferior divisions, and these divisions enter the orbit through the superior orbital fissure (and also through the common anular tendon). The superior and inferior divisions are typically separated by the nasociliary n. (of V1) and the optic n. (CN II).
The superior division of oculomotor n. efferently innervates:
levator palpebrae superioris m., and
superior rectus m.
The inferior division of oculomotor n. efferently innervates:
medial rectus m.,
inferior rectus m.,
inferior oblique m., and
transmits preganglionic parasympathetic fibers to:
ciliary ganglion (for sphincter pupillae muscles and ciliary muscles).
Note: The central artery of the retina is the first branch of the ophthalmic a. The central artery of the retina enters the dural sheath of the optic n. (CN II) and travels within the nerve to the retina.
Note: The inferior rectus m. originates from the common anular tendon (common tendinous ring), and inserts on the sclera of the inferior eye. The inferior rectus m. is innervated by the inferior division of the oculomotor n. (CN III). The inferior rectus m. depresses, adducts, and produces extorsion (lateral rotation) the eye.
Note: The inferior oblique m. originates from the orbital surface of the maxilla on the floor of the orbit, and inserts on the sclera of the inferior eye. The inferior oblique m. is innervated by the inferior division of the oculomotor n. (CN III). The inferior oblique m. elevates, abducts, and produces extorsion (lateral rotation) the eye.
Find these structures:
Lacrimal gland
Muscles
Levator palpebrae superioris m.
Common anular tendon
Superior rectus m.
Inferior rectus m.
Medial rectus m.
Lateral rectus m.
Superior oblique m.
Inferior oblique m.
Note: The common anular tendon (common tendinous ring) is the origin site for the rectus muscles. The ring encircles the optic nerve (CN II), superior and inferior divisions of the oculomotor n. (CN III), and abducens n. (CN VI).