Dissection 5 - The Orbit

Dissection Guide

Osteology and Surface Anatomy

• Roof of the orbit = orbital plate of frontal bone + lesser wing of sphenoid bone + floor of anterior cranial fossa

• Floor of orbit = Maxilla and zygomatic

• Foramina of the orbit: Optic canal, superior orbital fissure, inferior orbital fissure, supraorbital notch/foramen, infraorbital groove, infraorbital foramen, nasolacrimal canal

Conjunctivitis

• Pink eye

• From dilated blood vessels in the sclera surrounding the pupil and iris

Dissection - Superior → Inferior

• Layer 1: Roof of the orbit

• Layer 2: Periorbital membrane

• Layer 3: Frontal n. (branch of CN V1)

  • Branches into supraorbital and supratrochelar n.

• Layer 4: Levator palpebral superioris (innervated by CN III)

• Layer 5: Superior rectus muscle (innervated by CN III)

• Layer 6: Superior ophthalmic v.

Dissection - Lateral and medial

• Medial

  • Superior oblique m. parallels medial wall and goes through fibrocartilaginous trochlea

    • Innervated by CN IV (pierces lateral aspect of m.)

  • Medial rectus

  • Layer 2: Nasociliary n. (branching in the plane between superior oblique and more inferior than medial rectus)

• Lateral

  • Lateral rectus

  • Lacrimal n. course laterally toward lacrimal gland

  • Abducens n. enter medial side of lateral rectus (just anterior to apex of orbit)

• Note that all rectus muscles originate from the common tendenous (annular) ring that encircles the optic n.

• Optic a. is usually tortuous (allow mobility of the eye) and seen entering via the optic canal

Unilateral dissection

• Long ciliary n. branches off nasociliary n. on top of the or medial to optic n.

  • SS to cornea and conjunctiva and sympathetics to dilator pupillae

• Short ciliary n. lateral or superior to optic n. can be traced through the ciliary ganglion

Lacrimal gland

• SS from CN V1 (lacrimal n.)

• Preganglionic parasympathetics synapse at the pterygopalatine ganglion (before hitchhiking on V2 and V1)

Anterior orbit

• Lacrimal caruncle: medial angle of the eye

• Inferior oblique and inferior rectus can be seen from the front (incise lower eyelid)

• Nasolacrimal canal → Drains inferiorly into inferior nasal meatus

Venous Drainage of the Eye

• Primary drainage of the eye

  • Superior and inferior ophthalmic v. → Cavernous sinus posteriorly (primary)

  • Pterygoidplexus of veins (infratemporal fossa) inferiorly

  • Facial v. (anteriorly)

• Possible venous blood pathways around the eye

  • Supraorbital v. → Merge with angular v. → Superior ophthalmic v. → Cavernous sinus

  • Supratrochlear v. → Angular v. → Facial v.

  • Superior ophthalmic v. → Cavernous sinus

  • Inferior ophthalmic v. → Pterygoid plexus

  • Inferior ophthalmic v. → Superior ophthalmic v. → Cavernous sinus

  • Infraorbital v. → Pterygoid plexus

• Possible venous blood pathways of external orbit

  • Supraorbital v. → Merge with Angular v. → Superior ophthalmic v. → Cavernous sinus

  • Infraorbital v. → Through inferior orbital fissure → Pterygoid plexus

  • Lacrimal v. → Superior ophthalmic v. → Cavernous sinus

Bolded Terms

Abducent N.

• CN VI

• Pierces through middle of cavernous sinus → Superior orbital fissure → Lateral rectus

  • Pierces medial side of lateral rectus

Annular ring

• Tendons ring around optic n. where all 4 rectus muscles originate from

Anterior cranial fossa

• Floor of it contribute to roof of orbit

Ciliary ganglion

• Nasciliary n. → Ciliary ganglion → Short ciliary n. → Eye

• Where para/pre from CN III synapse

Conjunctiva

• Transparent membrane covering the inner portion of the eyelid and sclera

Cribiform plate

• Part of ethmoid plate on the medial side of the orbit

Frontal n.

• Most medial and superficial branch of the ophthalmic division of CN V

• Lays on top of levator palpebrae and branches into supraorbital and supratrochlear n.

Infraorbital groove

• Path for infraorbital n. (CN V2) to travel through on the floor of the orbit before exiting through the infraorbital foramen

Infraorbital foramen

• Infraorbital VAN (branch of V2) passes through

Inferior orbital fissure

• Zygomatic nerve, infraorbital vein, artery, and nerve

Inferior oblique m.

• Involved in elevation and ABduction

• Innervated by CN III

Inferior rectus m.

• Involved in Depression and ADDuction

• Innervated by CN III

Iris

Lacrimal caruncle

• On the medial potion of the eye, can be seen anteriorly

Lacrimal gland

• On the lateral upper corner

• SS innervation by CN V1 (lacrimal n.)

• Parasympathetics by CN VII

Lacrimal n.

• Most lateral branch of CN V1

Lateral rectus m.

• ABduction

• Innervated by CN VI

Lesser wing of sphenoid

Levator palpebrae superioris

• Must superior muscle right below the frontal n.

• Innervated by CN III

Long ciliary n.

• Branch of nasociliary n.

• Path for sympathetic innervation of dilator pupillae

Maxilla

• Contributes to the floor of the orbit

Medial rectus m.

• ADDuction

• Innervated by CN III

Nasociliary n.

• Most medial branch of CN V1

• Branches into long ciliary and ciliary ganglion → Short ciliary n.

Nasolacrimal canal

• Nasolacrimal canal → Drains inferiorly into inferior nasal meatus

Oculomotor n.

• CN III

Ophthalmic a.

• Branch of ICA that enters orbit with CN II

Optic canal

• CN II and opthalmic a. enter orbit

Optic n.

• CN II

Orobicularis oculi

• M. of facial expression that allows for forceful blinking

Orbital plate of the frontal

• Contributes to the roof of the orbit

Periorbital membrane

• Lays just below the bony roof of the orbit

Pupil

Sclera

Short ciliary n.

• Branches from the ciliary ganglion

Superior oblique m.

• Goes through trochlea before attaching to eye

• Depression and ABduction

• Innervated by CN IV

Superior ophthalmic v.

• Superior ophthalmic v. → Cavernous sinus

Superior orbital fissure

• CN III, IV, V1 and VI enter orbit

• Superior ophthalmic v. exits orbit to join cavernous sinus

Superior rectus m.

• Just deep to levator palpebrae

• Elevation and ADDuction

• Innervated by CN III

Supraorbital n.

• Branch of frontal n. that innervates lateral forehead

Supraorbital notch/foramen

• Where suprorbital VAN exits

Supratrochlear n.

• Branch of frontal n. that innervates medial forehead

Trochlea

• Fibrocartilagenous sling that supraorbital n. passes before attaching to eye

Trochlear n.

• CN IV

Zygomatic

• Forms lateral wall of orbit