Gross anatomy: orbit, eyelids, CN III, IV, VI

Question 1

General relationships of the orbit

Answer 1

• Superior: frontal sinus and anterior cranial fossa (frontal lobes)
• Posterior: middle cranial fossa (temporal lobes)
• Apex: cavernous sinus and sphenoid sinus (middle cranial fossa)
• Medial: ethmoid air cells (sinuses)- not nasal cavity
• Inferior: maxillary sinus

Question 2

General arrangement of orbital contents 1

Answer 2

• Periorbita: the periosteum that lines the orbit walls
• Orbital septum: layer of fascia on the anterior most parts of the orbit that close off the open orbit, extending from the orbit margin to the tarsal plates
• Tarsal plates: dense connective tissue within the upper and lower eyelids

Question 3

General arrangement of orbital contents 2

Answer 3

• Bulbar sheath: thin membranous fascia that separates the eyeball and the EOMs from other orbital contents
• Sclera: tough white outer layer of the eyeball to which the EOMs attach, continuous w/ cornea anteriorly and optic sheath posteriorly
• Optic sheath: continuous of meningeal layer of the bilaminar intracranial dura into the orbit around the optic nerve

Question 4

Eyelids 1

Answer 4

• From superficial to deep
• Skin on eyelids is thin and loose, cutaneous innervation of upper eyelid by opthalmic nerve (V1), and the lower lid by infraorbital nerve (branch of V2)
• Subcutaneous fat: little fat, but the eyelashes (cilia) and associated sebaceous glands are associated w/ this layer

Question 5

Eyelids 2

Answer 5

• Muscular layer: comprised of the levator palpebrae superioris muscle (open lids) inserting into the superior tarsal plate and interdigitating w/ the obicularis oculi muscle (closing lids, CN VII)
• Tarsofascial layer: the orbital septum inserting into the tarsal plates, tarsal glands empty along free margins of eyelids
• Superior tarsal muscle: smooth muscle arising from levator palpebrae and inserting into tarsal plate, contracts tonically to maintain elevated upper eyelid (innervated by sym/post axons from superior cervical ganglion)

Question 6

Cunjunctiva

Answer 6

• Palpebral conjunctiva: thin epithelium covering the inside of the lid, continuous w/ bulbar conjunctiva covering the sclera (innervated by same nerves that supplies sensory to the cutaneous skin of each lid)
• Conjunctival sac: palpebral conjunctiva covers inner surface of lids and bulbar conjunctiva covers surface of eyeball (continuous w/ each other)
• Superior and inferior fornices are the boundaries of the sac
• These two membranes are separated by a thin film of tears

Question 7

Clinical correlations of eyelids and conjunctiva

Answer 7

• Sty: inflammation of a sebaceous gland of the eyelash
• Chalazion: inflammation of the tarsal gland of the tarsal plate
• Conjunctivitis: inflammation of bulbar or palpebral conjunctiva
• Blood shot: local congestion of small vessels btwn bulbar conjunctiva and sclera that causes vessel dilation
• Ptosis: drooping of upper eyelid due to paralysis of superior tarsal muscle (little ptosis) or levator palpebrae superioris (big ptosis)

Question 8

Direction of eye movements

Answer 8

• Elevation: look up
• Depression: look down
• Abduction: look away from midline (lateral rotation)
• Adduction: look toward midline (medial rotation)
• Intorsion and extorsion: rotation of pupil around anterior-posterior axis (pupils move clockwise, medially = intorsion vs pupils move counter-clockwise, laterally = extorsion)

Question 9

Extraocular muscles (EOMs)

Answer 9

• ALL EOMs (except lateral and medial rectus) attach medially to the vertical axis
• All EOMs arise from the apex of the orbit and extend anteriorly, except the inferior oblique which arises anteriorly and extends posteriorly
• All rectus muscles insert into the anterior hemisphere of the eye
• All oblique muscles insert into the posterior hemisphere of the eye
• The superior oblique muscle arises from the apex, travels anteriorly, then thru the trochlea and turns back to attach in the posterior hemisphere
• Lateral rectus innervated by CN VI, superior oblique innervated by CN IV, all others by CN III

Question 10

Direction of eye movements conveyed by the EOMs

Answer 10

• Superior rectus (III): elevates and adducts, since it attaches at the superior, anterior aspect, midline to the vertical, and pulls backward
• Inferior rectus (III): depresses and adducts, since it attaches at the inferior, anterior aspect, midline to the vertical, and pulls backward
• Medial rectus (III): adducts only
• Lateral rectus (VI): abducts only
• Superior oblique (IV): depresses and abducts, since it attaches at the superior, posterior aspect, midline to the vertical and pulls forward
• Inferior oblique (III): elevates and abducts, since it attaches at the inferior, posterior aspect, midline to the vertical and pulls forward

Question 11

Functional eye movements

Answer 11

• Unifunctional muscles: medial and lateral rectus only have a single job (adduct and abduct, respectively)
• Multifunctional muscles: inferior and superior rectus both adduct, as well as either depression or elevating. Superior and inferior obliques both abduct as well as depressing or elevating
• Therefore to only elevate or depress both an oblique and superior/inferior rectus must activate
• Ex: to see down must activate the inferior rectus + superior oblique, since they both depress but the adduction from the inferior rectus will be canceled by the abduction from the superior oblique (exact opposite for elevation)

Question 12

Testing EOMs

Answer 12

• To test multifunctional muscles, first activate the opposite unifunctional muscle
• Therefore, to test the depression ability of the superior oblique, first adduct the eye using the medial rectus
• This isolates the function of the superior oblique to only depression

Question 13

Oculomotor nerve (CN III)

Answer 13

• middle cranial fossa-> wall of cavernous sinus-> superior orbital fissure-> orbit-> upper and lower divisions that supply the EOMs
• Motor component: oculomotor nucleus (III)-> CN III-> 5 of 7 EOMs (levator palpebrae, superior rectus, inferior rectus, medial rectus, inferior oblique)
• Parasympathetics: Edinger-westphal nucleus (III) para/pre cell bodies-> CN III-> ciliary ganglion (para/post cell bodies)-> ciliary nerves-> ciliary body (accommodation) + sphincter pupillage muscle (constriction of pupil)

Question 14

Trochlear nerve (CN IV)

Answer 14

-Motor only: trochlear nucleus (cell bodies)-> middle cranial fossa-> wall of cavernous sinus-> superior orbital fissure-> orbit- superior oblique only

Question 15

Abducent nerve (CN VI)

Answer 15

-Motor only: abducent nucleus (cell bodies)-> posterior cranial fossa-> through cavernous sinus-> superior orbital fissure-> orbit-> lateral rectus only

Question 16

Opthalmic nerve (V1)

Answer 16

• Provides sensory innervation to the skin of the upper face, the sensory cell bodies are in the trigeminal ganglion
• Has many branches (medial to lateral): nasociliary nerve, frontal nerve, lacrimal nerve (NFL)
• Innervates the upper eyelid, both conjunctiva and cutaneous (nasociliary + frontal)
• Bulbar conjunctiva: innervated by nasociliary branch of V1, which gives rise to ciliary nerves. Axons may pass thru the ciliary ganglion (but will not synapse)
• Axons from III that do synapse in the ciliary ganglion will also travel on the ciliary nerves
• Corneal reflex: sensory nerves of V1 cause you to blink by contracting obicularis oculi (VII)

Question 17

Maxillary nerve (V2)

Answer 17

• Sensory to midface and lower eyelid
• Innervates lower conjunctiva and cutaneous skin (infraorbital branch)
• Infraorbital branch courses thru the infraorbital groove, canal, and foramen in the floor of the orbit

Question 18

Facial nerve (VII)

Answer 18

• Provides parasympathetic innervation to the lacrimal gland, using V1/V2 as a hitchhiking nerve
• Para/pre cell bodies in superior salvatory nucleus, then runs on VII
• After moving from nerve to nerve (doesn’t remain on VII), the axons synapse on the pterygopalatine ganglion (para/post cell bodies)
• Once para/post, the axons jump onto the maxillary nerve and then opthalmic nerve to reach the lacrimal nerve (branch of V1) to reach the lacrimal gland

Question 19

Oculomotor (III) parasympathetics

Answer 19

• Para/pre cell bodies in EWN, the axons course in CN III and synapse in the ciliary ganglion (para/post cell bodies)
• Para/post axons then travel thru ciliary nerves (part of V1) to eye ball (specifically the ciliary body for accommodation and the spinster pupillae muscle for pupil constriction)

Question 20

Sympathetics to the eye 1

Answer 20

• Sym/pre cell bodies in the lateral horn cells of T1-T4/5 in SC
• Sym/pre axons enter the sympathetic trunk (ventral root-> spinal nerve-> white communicating rami) then ascend to superior cervical ganglion
• Superior cervical ganglion contains all sym/post cell bodies for head and neck (including eyes)
• From the superior cerivcal ganglion, the sym/post axons jump on the ICA, and course along it as the carotid plexus

Question 21

Sympathetics to the eye 2

Answer 21

• In the cavernous sinus the sym/post destined for the superior tarsal join CN III and run to the superior tarsal, which extends inferiorly off the levator palpebrae (since CN III innvervates the levator palpebrae)
• Superior tarsal keeps the upper eyelid above the eye, against gravity (tonic activation)
• In the cavernous sinus the sym/post destined for the dilator pupillae muscles join either the nasociliary nerve (branch of V1) or CN III to reach the ciliary nerves and then the eyeball

Question 22

Horner’s syndrome

Answer 22

• Due to interruption of the sympathetics to the face/eye
• Causes ptosis (little ptosis) due to lack of innervation of the superior tarsal and thus drooping of the eyelid
• Miosis (constriction of the pupil) due to lack of sympathetics to the dilator pupillae and thus unopposed parasymp activity of the sphincter pupillae
• Anhydrosis: dry skin due to inability to perspire
• Vasodilation of the vessels due to lack of sympathetics to cause vasoconstriction