Session 6: The Orbit [Complete]

Question 1

What makea up the following of the orbit:

i. Roof
ii. Floor
iii. Lateral wall

Answer 1

Roof: orbital plate of the frontal bone

Floor: orbital plate of the maxilla

Lateral wall: Zygoma and greater wing of sphenoid

Question 2

What makes up the medial wall of the orbit?

Answer 2

Frontal process of maxilla

Lacrimal bone

Orbital plate of ethmoid bone

Lesser wing of sphenoid

Question 3

Describe the contents of the Optic canal

Answer 3

Optic nerve (II)

Ophthalmic artery (first branch of the internal carotid artery distal to the cavernous sinus)

Question 4

Describe the contents of the inferior orbital fissure

Answer 4

V2 [Maxillary nerve] [Specifically the zygomatic nerve which is a branch of V2]

infraorbital vessel

Question 5

Describe the contents of the superior orbital fissure.

Answer 5

Occulomotor nerve CN3

Trochlear nerve CN4

Abducens CN6

V1 [Ophthalmic nerve/ CN 5]

Opthalmic vein and sympathetic fibres (running with vessels)

Question 6

In which bones are the foramina of the orbit found?

Answer 6

Optic canal- lesser wing of sphenoid

Superior orbital fissure- between the lesser and greater wings of the sphenoid bone

Inferior orbital fissure- sphenoid bone and maxilla

(posterior wall of the eye too, as the orbital plate of the maxilla runs back! (frontal process of maxlla is one of bones making up medial wall of orbit)

Question 7

What are the extrinsic muscles of the eye?

Answer 7

The 4 recti muscles

The oblique muscles of the eye

Question 8

Where is the origin of the 4 recti muscles and where do they insert?

Answer 8

Origin: Common tendinous ring

Insert: Sclera (white of the eye), 5mm behind corneal margin

Question 9

Describe the nerve supply to rectus muscles

Answer 9

medial, superior and inferior rectus = CN3 (Occulomotor)

lateral rectus muscle = CN6 (Abducens)

Question 10

What are the names of the 2 oblique muscles of the eye?

Answer 10

inferior oblique muscle and superior oblique muscle

Question 11

What are the origins of the oblique muscles?

Answer 11

Inferior: orbital surface of maxilla

Superior: body of the sphenoid

Question 12

What are the insertions of the oblique muscles?

Answer 12

Superior: posterior/superior quadrant of the eye, via trochlea (bony spur in the orbit)

Inferior: posterior/inferior quadrant of the eye

Question 13

Describe the nerve supply of the oblique muscles

Answer 13

inferior is CN3 (Occulomotor)

superior is CN4 (Trochlear)

Question 14

What is the origin, insertion and nerve supply of the levator palpebrae superioris (LPS)?

Answer 14

Origin=lesser wing of sphenoid

Insertion= superior tarsal plate and skin of eyelid

Nerve supply= CNIII + Sympathetic nerves to smooth muscle

Question 15

Why is sympathetic supply of LPS clinically important?

Answer 15

Because in horners syndrome which involves loss of sympathetic ouput to head and neck, there is drooping of the eyelid (=ptosis).

There is also a lack of sweating, constricted pupils and enopthalmos in this condition.

Question 16

What is the trochlea?

Answer 16

a small bony spur on the medial part of orbit

Question 17

Describe the isolated contraction of the superior oblique muscle.

Answer 17

down and out *depressor and abductor*

Question 18

Describe the isolated contraction of the inferior oblique muscle.

Answer 18

up and out *elevator and abductor*

Question 19

Describe the isolated contraction of the superior and inferior recti.

Answer 19

Superior rectus: elevates and adducts

Inferior rectus: depresses and adducts

Question 20

Describe the isolated contraction of the lateral and medial rectus muscles.

Answer 20

Lateral rectus muscle: Abducts

Medial rectus muscle: Adducts

Question 21

How do you test the function of the lateral and medial rectus?

Answer 21

Tracking (moving finger left and right), but remember that version will involve opposite muscle in each eye

Question 22

How do you test the function of the superior oblique muscle?

Answer 22

They have to adduct that eye, and look down *this removes the effect of the inferior rectus on depression of eye*

Question 23

How do you test the function of inferior rectus?

Answer 23

you have to abduct the eye and ask them to look down *this removes the effect of the superior oblique on depression of the eye*

Question 24

How do you test the function of the inferior oblique muscle?

Answer 24

Adduct the eye and look up *removes the effect of superior rectus*

Question 25

How do you test the function of the superior rectus muscle?

Answer 25

Abduct the eye and look up and up \*removes effect of inferior oblique\*

Question 26

Describe the nerves of the orbit

Answer 26

1) Optic nerve [CN2]: provide retinal ganglion cell axons 2) Oculomotor [CN3]: Provides motor fibres to the superior, medial and inferior recti, inferior oblique and to the levator palpebrae superioris. It also provides parasympathetic fibres. It has 2 rami: The superior branch innervates superior rectus and LPS, and the inferior branch innervates everything else. Sympathetic nerves from the internal carotid plexus travel with the superior branch of occulomotor to innervate the superior tarsal muscle , which helps maintain opened eyelid (after LPS has opened it) 3) Trochlear [CN4]: Provides motor fibres to superior oblique muscles 4) Abducens [CN6]: Porvides motor fibres to levator rectus 5) Ophthalmic division of trigeminal nerve [CN5] 6) Cilliary ganglion

Question 27

What are the branches of the ophthalmic division of the trigeminal nerve?

Answer 27

Lacrimal Frontal [further branches to supratrochlear and supraorbital] Nasociliary [Further branches to the cilliary ganglion and branches to ethmidal and infratrochlear]

Question 28

What is the cavernous sinus and where is it located in relation to the orbit? Describe the order of nerves in the lateral wall of the cavernous sinus and where they enter the orbit.

Answer 28

The cavernous sinus is where the nerves travel, after emerging from the brainstem, just before they're about to go into the superior and inferior orbital fissure. It is located postero-medially to the orbit. So in the order they emerge from the brainstem: Oculomotor Trochlear Abducens (More medially) Opthalmic branch of trigeminal (V1) Maxillary branch of the trigeminal (V2). The oculomotor, trochlear, abducens and V1 then go through the superior orbital fissure. V2 then goes through the inferior orbital fissure.

Question 29

Which nerve runs near the internal carotid artery and is thus a bit furhter from the wall of the cavernous sinus?

Answer 29

Abducens CN6

Question 30

State the clinical relevance of the nerves in the cavernous sinus

Answer 30

Infection or cavernous sinus thrombosis can lead to problems in the functions of nerves located there.

Question 31

What are the branches of the lacrimal, frontal and nasociliary branches of V1?

Answer 31

Lacrimal (none listed) Frontal- supratrochlear and supraorbital (which emerges through supraorbital foramen to supply forehea) Nasociliary- branch to ciliary ganglion, ethmoidal and infratrochlear

Question 32

Outline the nerves in the preganglionic and post ganglionic parasynpathetic innervation to eye. Which muscle(s) are innervated?

Answer 32

The cilliary ganglion provides parasympathetic fibres. Preganglionic nerves to cilliary ganglion are supplied from the inferior rami of the the occulomotor nerve Postganglionic nerves originating from the cilliary ganglion are loctaed in short ciliary nerves which innervate the ciliary muscle and the spinchter pupillae

Question 33

What does the ophthalmic artery divide into?

Answer 33

central artery of the retina muscular branches ciliary arteries lacrimal artery supratrochlear artery supraorbital artery

Question 34

What do opthalmic veins divide into?

Answer 34

Superior opthalmic veins drain into cavernous sinus (route of infection) Inferior opthalmic vein drains into the pterygoid plexus

Question 35

Swelling at the back of the eye (optic disc) is known as? What does it usually indicate?

Answer 35

Swelling of the optic disc is known as papilloedema. It indicates inreased intracranial pressure

Question 36

What are the main components which make up the lacrimal system?

Answer 36

Lacrimal gland Lacrimal sac Nasolacrimal duct

Question 37

State the innervation of the lacrimal gland

Answer 37

Parasympathetic secretomotor fibres (CNVII) [Facial] from pterygopalatine ganglion via the zygomaticotemporal nerve (which is a branch of V2) Also innervated by lacrimal nerves

Question 38

Where is the lacrimal sac located?

Answer 38

medial canthas of the eye

Question 39

Where does the nasolacrimal duct drain?

Answer 39

Into the internal meatus of the nose

Question 40

Outline the autonomic control of the eyelid.... What is the effect of the following: 1. Damage to the oculomotor nerve 2. Damage to sympathetic nerves

Answer 40

CN3 innervates levator palpabrae superioris which opens both of the eyelids. Damage to this nerve results in significant ptosis. LPS is skeletal muscle so has somatic input. Attached to the LPS is the superior tarsal muscle. This muscle helps the eyelid to remain open once it has been opened by LPS. It is sometimes referred to as the smooth muscle component of LPS and is innervated by sympathetic fibres and it will cause a slight ptosis if the sympathetic nerves are damaged e.g. in horners syndrome