TBL29 - Extraocular Muscles, Nerves and Vessels

Question 1

What muscle elevates the upper eyelid? Recognize the locations of the superior and inferior oblique muscles and the superior, inferior, medial, and lateral rectus muscles.

Answer 1

The levator palpebral muscle elevates the upper eyelid

Question 2

What do the medial and lateral rectus muscles do to the pupil, respectively? What function do the superior oblique and inferior rectus muscles serve, respectively? Together, what do the superior oblique and inferior rectus muscles do?

Answer 2

1) The medial rectus and lateral rectus muscles adduct and abduct the pupil
2) The superior oblique muscle depresses and abducts the pupil and the inferior rectus muscle depresses and adducts the pupil
3) Thus, together the superior oblique and inferior rectus depress the pupil straight downward

Question 3

What function do the inferior oblique and the superior rectus muscles serve, respectively? Together, what do the inferior oblique and superior rectus muscles do?

Answer 3

1) The inferior oblique muscle elevates and abducts the pupil and the superior rectus muscle elevates and adducts the pupil
2) Thus, together the inferior oblique and superior rectus elevate the pupil straight upward

Question 4

How would a patient be tested to compare functional integrity of the superior oblique and inferior rectus muscles, and the inferior oblique and superior rectus muscles?

Answer 4

1) When the eye is initially abducted by LR, only the rectus muscles can produce elevation and depression
2) When the eye is initially adducted by MR, only the oblique muscles can produce elevation and depression
3) Following movements of the examiner’s finger, the pupil is moved in an extended H-pattern to isolate and test individual extra-ocular muscles and the integrity of their nerves

Question 5

What are the names of CN III, CN IV, & CN VI and where do they pass from and to? What is a mnemonic device to learn for innervation of the extraocular muscles?

Answer 5

1) The occulomotor nerve (CN III), trochlear nerve (CN IV), and abducent nerve (CN VI) pass from the middle cranial fossa through the superior orbital fissure into the orbit
2) LR6SO4AO3 as a mnemonic device for innervation of the extraocular muscles

Question 6

As the internal carotid artery courses toward the anterior clinoid processes, what does it pass between? What CNs course anteriorly with the internal carotid artery?

Answer 6

1) As the internal carotid artery courses toward the anterior clinoid process, it passes between the vascular channels of the cavernous sinus
2) CNs III, IV, VI, CN V1, and CN V2 course anteriorly with the artery

Question 7

How do CN III and CN VI palsies differ? Why is CN IV paralysis characterized by diplopia when looking downward?

Answer 7

1) a) CN III Palsy - The pupil is fully abducted and depressed (“down and out”) because of the unopposed activity of the lateral rectus and superior oblique, respectively
b) When the abducent nerve (CN VI) supplying only the lateral rectus is paralyzed, the individual cannot abduct the pupil on the affected side (abducent nerve palsy or paralysis). The pupil is fully adducted by the unopposed pull of the medial rectus
2) One or more extra-ocular muscles may be paralyzed by disease in the brainstem or by a head injury, resulting in diplopia (double vision). Two different focal points; CN IV superior oblique

Question 8

How can fractures of the cranial base result in pulsating exophthalmos and which nerves may be affected?

Answer 8

1) In fractures of the cranial base, the internal carotid artery may be torn, producing an arteriovenous fistula within the cavernous sinus
2) Arterial blood rushes into the cavernous sinus, enlarging it and forcing retrograde blood flow into its venous tributaries, especially the ophthalmic veins
3) As a result, the eyeball protrudes (exophthalmos) and the conjunctiva becomes engorged (chemosis)
4) The protruding eyeball pulsates in synchrony with the radial pulse, a phenomenon known as pulsating exophthalmos
5) Because CN III, CN IV, CN V1, CN V2, and CN VI lie in or close to the lateral wall of the cavernous sinus, these nerves may also be affected when the sinus is injured

Question 9

Where is the parasympathetic ciliary ganglion located in relation to the orbit? What nerve does the nasociliary nerve arise from in the orbit?

Answer 9

1) The parasympathetic ciliary ganglion is in the posterior extent of the orbit
2) The nasociliary nerve arises from CN V1 in the orbit

Question 10

Where do presynaptic parasympathetic fibers from CN III synapse? What nerve do postsynaptic fibers join, what is this nerve a branch of, and where is this nerve transported to? What nerve fibers supply the posterior aspect of the eye?

Answer 10

1) Presynaptic parasympathetic fibers from CN III synapse in the ciliary ganglion
2) Postsynaptic fibers join the short ciliary nerve, a branch of nasociliary nerve, for transport to the ciliary muscle and pupillary constrictor
3) Somatic sensory fibers of the short ciliary nerve supply the posterior aspect of the eye

Question 11

What is the long ciliary nerve a branch of and what does it conduct to the trigeminal ganglion? What does the long ciliary nerve transport postsynaptic sympathetic fibers to?

Answer 11

1) The long ciliary nerve, another branch of the nasociliary nerve, conducts somatic sensations from the cornea to the trigeminal ganglion
2) The long ciliary nerve also transports postsynaptic sympathetic fibers to the pupillary dilator muscle

Question 12

What are the nerve injuries when the pupillary reflex or corneal reflex is lost?

Answer 12

1) This reflex, involving CN II (afferent limb) and CN III (efferent limb), is the rapid constriction of the pupil in response to light
2) Corneal reflex is CN V1 (afferent limb) and CN VII (efferent limb)

Question 13

Why do pupillary constriction and ptosis occur with Horner’s Syndrome?

Answer 13

1) Constriction of the pupil occurs because the parasympathetically stimulated sphincter of the pupil is unopposed
2) The ptosis is a consequence of paralysis of the smooth muscle fibers interdigitated with the aponeurosis of the levator palpebrae superioris that collectively constitute the superior tarsal muscle, supplied by sympathetic fibers

Question 14

Where does the ophthalmic artery arise from? Where does the artery enter the orbit? In the orbit, what does the ophthalmic artery generate?

Answer 14

1) The ophthalmic artery arises from the internal carotid artery at its 180⁰ turn under the anterior clinoid process
2) The artery enters the orbit via the optic canal adjacent to CN II
3) In the orbit, the ophthalmic artery generates the central retinal artery and the ciliary artery

Question 15

What vein does the supraorbital vein drain into and where does this vein traverse and empty into? What vein do branches of the ciliary vein drain into and where does this vein empty into?

Answer 15

1) The supraorbital vein drains into the superior ophthalmic vein that traverses the superior orbital fissure and empties into the cavernous sinus
2) Branches of the ciliary vein (ignore vorticose veins) drain into the inferior ophthalmic vein that empties mainly into the cavernous sinus or into the pterygoid venous plexus in the infratemporal fossa

Question 16

What does the central retinal vein traverse and drain into?

Answer 16

The central retinal vein traverses the optic canal and drains into the cavernous sinus

Question 17

How can thrombi in the ophthalmic artery or cavernous sinus cause blindness?

Answer 17

1) Because terminal branches of the central artery of the retina are end arteries, obstruction of them by an embolus results in instant and total blindness
2) Because the central vein of the retina enters the cavernous sinus, thrombophlebitis of this sinus may result in the passage of a thrombus to the central retinal vein and produce blockage of the small retinal veins