The Orbit

Question 1

Which bones are these?

Answer 1

Question 2

Roof, lateral + floor of orbit?

Answer 2

Roof = frontal bone
Lateral = zygoma
Floor = maxilla

Question 3

What is this?
Formed by?
Purpose?

Answer 3

Infraorbital foramen
Formed by maxilla
Purpose = infraorbital branch of CNV2 exits skull to provide sensory innervation to face

Question 4

What is this?
Formed by?
Purpose?

Answer 4

Supraorbital ridges
Formed by frontal bone
Purpose = deflect blows away from the eyes

Question 5

What is this?

Purpose?

Answer 5

Frontal notch/foramen

For supraorbital nerve and artery

Question 6

Label this

Answer 6

Question 7

Lacrimal bone associated with?

Answer 7

Nasolacrimal duct that carries excess lacrimal fluid (tears) into the nasal cavity

Question 8

Sphenoid bone foramina? (3)
+ nerves that travel through them

What contributes?

Answer 8

Optic canal (CN II)
Superior orbital fissure (CN 3, 4, 5, 6)
Inferior orbital fissure (opthalmic veins)

Tiny contribution from palatine bone in wall of inf. orbital fissure

Question 9

Label this

Answer 9

Question 10

function?

Answer 10

Suspensory ligaments support eyeball

Check ligaments restrict medial and lateral recti

Question 11

Answer 11

the sclera provides an attachment site for the recti muscles

Question 12

aqueous humor found?
function?
made by?
circulation?

Answer 12

anterior chamber of eye - space between the lens and the cornea (anterior to lens)

helps to maintain intra-ocular pressure

Made by ciliary body, drains into corneo-scleral junction (canal of Schlemm)

Question 13

posterior chamber of eye?
filled with?
function?

Answer 13

behind lens
vitreous humor
vitreous humor supports retina

Question 14

intraocular muscles?

innervation?

Answer 14

also ciliary muscle (changes lens shape) - occulomotor nerve

Question 15

Answer 15

…

Question 16

Answer 16

….

Question 17

extraocular muscles?

Answer 17

7 extraocular muscles -
levator palpebrae superioris from orbital roof to upper eyelid

Superior, inferior, medial and lateral recti from annular ring to sclera (anterior to equator)

Superior oblique (lesser wing sphenoid) and inferior oblique (orbital floor) to sclera (posterior to equator)

Question 18

Answer 18

..

Question 19

Answer 19

RADSIN is a mnemonic to help you remember the Recti ADDuct (except for lateral rectus) and the Superiors INtort (roll the posterior part of the eye inwards). The chemical style formula helps with the nerve supply – all are oculomotor except Lateral Rectus (CN VI) and Superior Oblique (CN IV).

Question 20

CN II pathway?

Answer 20

The optic nerve leaves the orbit via the optic canal. CN II forms a chiasma over the pituitary fossa, then sends optic tracts towards the brain (for example, to the thalamus). The optic radiations then take information to be processed in the primary visual cortex. These communicate with association areas to put the images into context (give them meaning).

Question 21

other ocular nerve other than CN II?

Answer 21

The other cranial nerves pass through the superior orbital fissure to enter the orbit and supply the intrinsic and extrinsic muscles of the eye. The trigeminal nerve supplies sensory innervation to the orbit and carries fibres from the facial nerve to the lacrimal gland.

Question 22

what do ocular nerves pass through before superior orbital fissure?

Answer 22

cavernous sinus

Before the nerves reach the superior orbital fissure, they pass though the cavernous dural venous sinus. This lies around the body of the sphenoid bone and the pituitary fossa. CN III, CN IV and CN V pass along the walls close to the dura. CN VI passes through the middle of the sinus close to the internal carotid artery. So, the abducent nerve is the odd one out here.

Question 23

Answer 23

As the nerves come into the posterior part of the orbit, they reach an annular ring of connective tissue that provides an attachment site for the recti muscles. Some nerves pass through the ring, but parts of the trigeminal nerve (frontal and lacrimal) and CN IV do not. So, the trochlear nerve is the odd one out here.

Question 24

ophthalmic division trigeminal pathway?

branches?

Answer 24

ophthalmic division passes into the superior orbital fissure

frontal, nasocilliary, lacrimal
frontal divides to form supraorbital + supratrochlear branches which pass onto the face via the supraorbital notch to supply sensory innervation to the skin of the forehead

The nasociliary branch will form ethmoidal branches which pass through the ethmoid bone and will be discussed further in the presentation on the nose.

The lacrimal nerve acts as a carrier for parasympathetic secretomotor fibres from the facial nerve.

Question 25

Answer 25

frontal branch passes over the superior surface of levator palpebrae superioris

Question 26

occulomotor nerve divisions

Answer 26

ssuperior division = supplies levator palpebrae superioris and superior rectus with motor innervation The inferior division = supplies medial rectus, inferior rectus and inferior oblique with motor innervation. It also carries parasympathetic fibres to the intrinsic muscles of the eye. The ciliary ganglion is a small piece of nerve tissue posterior to the eye which communicates with CN III and sends short ciliary nerves into the eyeball

Question 27

Answer 27

CN VI and CN IV are small as they only supply one muscle each. CN VI can be seen associated with the surface of lateral rectus and CN IV crosses the superior surface of superior oblique before piercing and innervating it.

Question 28

blood supply to orbit? | pathway?

Answer 28

The blood supply to the orbit is from the ophthalmic artery – a branch of the internal carotid artery. The ophthalmic artery also gives branches to the forehead and scalp (supraorbital supratrochlear, and zygomaticotemporal), to the nose (dorsal nasal and ethmoidal arteries). The ophthalmic artery enters the orbit through the optic canal with the optic nerve.

Question 29

venous drainage orbit?

Answer 29

The ophthalmic veins of the orbit communicate with the cavernous venous sinus through the superior orbital fissure + with the pterygoid venous plexus through the inferior orbital fissure + with the facial vein. This creates a potential for the spread of infection from external structures to internal structures such as the dural meninges.

Question 30

Answer 30

The tears wash across the surface of the eye and then are gathered through lacrimal punctum into the lacrimal canaliculi and then into a membrane lined space called the lacrimal sac. This sac communicates with the inferior meatus of the nose via the nasolacrimal duct

Question 31

Answer 31

The facial nerve provides secretomotor fibres to the submandibular and sublingual salivary glands via the chorda tympani by joining with the lingual nerve (CNV3). The fibres to the lacrimal gland also travel with the trigeminal nerve but in this case CNV2 and V1. The facial nerve branches to form the greater petrosal nerve (named as it passes across the petrous part of the temporal bone and is the bigger nerve – lesser petrosal is related to the pathway of CN IX to the parotid). It carries parasympathetic secretomotor fibres. It then joins with sympathetic fibres from a plexus around the internal carotid artery (called the deep petrosal nerve) to form the nerve of the pterygoid canal. This nerve passes to the pterygopalatine ganglion (at the fissure on the wall of the infratemporal fossa) to join with CNV2 (zygomatic branch) these fibres then join the lacrimal nerve (CNV1) to finally reach the lacrimal gland. So, lesser petrosal and greater petrosal are parasympathetic from CN IX and CN VII respectively. Deep petrosal are sympathetic fibres, and the nerve of the pterygoid canal has both type of fibres present.