6.1 The orbit and its contents

Question 1

What is the superior margin of the orbit formed by?

Answer 1

frontal bone, presents near its medial end either a supraorbital notch or a supraorbital foramen

Question 2

What is the lateral margin of the orbit formed by?

Answer 2

zygomatic process of the frontal bone and the frontal process of the zygomatic bone

Question 3

What is the inferior margin of the orbit formed by?

Answer 3

zygomatic and maxillary bones

Question 4

What is the medial margin of the orbit formed by?

Answer 4

frontal process of the maxilla

Question 5

what is the roof (superior wall) of the orbit formed by?

Answer 5

frontal bone and lesser wing of sphenoid

Question 6

what is the floor (inferior wall) of the orbit formed by?

Answer 6

maxilla, palatine and zygomatic bone

Question 7

what is the medial wall of the orbit formed by?

Answer 7

ethmoid, maxilla, lacrimal and sphenoid

Question 8

what is the lateral wall of the orbit formed by?

Answer 8

zygomatic bone and greater wing of thesphenoid

Question 9

Theoptic canalis a cylindrical canalrunning obliquely through the _________________ near the base where it joins the body of sphenoid

It connects the ___________ to the orbit

The____________is the opening to theoptic canal

The optic canal transmits ________________

Answer 9

lesser wing of sphenoid bone;

anterior cranial fossa;

optic foramen;

Optic nerve (CN II); Ophthalmic artery

Question 10

The superior orbital fissure is a foramen in the skull, although strictly it is more of a cleft, lying between the __________________________.

Answer 10

lesser and greater wings of the sphenoid bone

Question 11

what does the lateral part of the superior orbital fissure transmit? (LFTS)

Answer 11

• Superior ophthalmic vein
• Lacrimal nerve (CN V1)
• Frontal nerve (CN V1)
• Trochlear nerve (CN IV)

Question 12

what does the middle part of the superior orbital fissure transmit? (NASI)

Answer 12

• Superior and inferior divisions of the oculomotor nerve (CN III)
• Nasociliary nerve (CN V1)
• Abducent nerve (CN VI)

Question 13

what does the medial part of the superior orbital fissure transmit?

Answer 13

Inferior ophthalmic veins

Question 14

• Orbital cellulitis most commonly occurs when bacterial infection spreads from the paranasal sinuses, most often from the ethmoid sinus through the __________________
• It can also occur when an eyelid skin infection or an infection in an adjacent area spreads to the orbit or from an infection in the blood system
• The drainage of the eyelids, sinuses and orbits is largely throughout the orbital venous system: more specifically, through the superior and inferior orbital veins that drain into the cavernous sinus
• This venous system is devoid of valves and for this reason infection might spread, in preseptal and orbital cellulitis, into the cavernous sinus causing a sight threatening complication such as _________________

Answer 14

thin lamina papyracea of the medial orbital wall;

cavernous sinus thrombosis

Question 15

The major arterial supply to the orbit is the ophthalmic artery, the first major branch of the ________________

• It courses ________________ and enters the orbit through the optic canal
• In general, the branches of the ophthalmic artery can be divided into 3 groups of vessels (ocular, orbital, extraorbital), based on their target organs

Answer 15

internal carotid artery;

inferior aspect of the optic nerve

Question 16

What are the ocular branches of the opthalmic artery?

Answer 16

central retinal artery, ciliary arteries, and collateral branches to the optic nerve

Question 17

What are the orbital branches of the opthalmic artery?

Answer 17

lacrimal artery, muscular arteries, and periosteal branches

Question 18

What are the extraorbital branches of the opthalmic artery?

Answer 18

posterior and anterior ethmoid arteries, supraorbital artery, medial palpebral artery, dorsal nasal artery, and supratrochlear artery

Question 19

Venous drainage of the orbit occurs through 2 major veins, the ____________________

• The orbital veins are ____________
• Therefore, direction of venous drainage depends on pressure gradients

The superior ophthalmic vein collects flow from the ethmoidal, ciliary, lacrimal, and superior vortex tributaries

The vein passes through the _____________________ and drains into the ______________

Answer 19

superior and inferior ophthalmic veins ;

valveless;

superior orbital fissure;

cavernous sinus

Question 20

The inferior ophthalmic vein is supplied by a diffuse plexus of veins in the floor of the orbit

• The inferior ophthalmic vein empties into the ______________ within the orbit and has a small branch, which drains into the _______________
• The central retinal vein empties directly into the ______________
• The veins of the external orbit drain into the _____________ of the face that has connections with the superior ophthalmic vein system.

Answer 20

superior ophthalmic vein;

pterygoid venous plexus;

cavernous sinus ;

angular vein

Question 21

Theoculomotor nerveoriginates from the oculomotor nucleus located within the _________________

• It emerges from the anterior aspect of the midbrain
• Passing inferiorly to the posterior cerebral artery and superiorly to the superior cerebellar artery

The nerve then pierces the dura mater and enters the __________________ of thecavernous sinus

• Within the cavernous sinus, it receives _____________________
• These fibres do not combine with the oculomotor nerve – they merely travel within its sheath

The nerve leaves the cranial cavity via the________________

Answer 21

midbrain at the level of the superior colliculus;

lateral aspect;

sympathetic branches from the internal carotid plexus;

superior orbital fissure

Question 22

What does the superior branch of the oculomotor nerve innervate?

Answer 22

• provides motor innervation to the superior rectus and levator palpabrae superioris
• Sympathetic fibres run with the superior branch to innervate the superior tarsal muscle

Question 23

What does the inferior branch of the oculomotor nerve innervate?

Answer 23

• Provides motor innervation to the inferior rectus, medial rectus and inferior oblique
• Also supplies pre-ganglionic parasympathetic fibres to the ciliary ganglion, which ultimately innervates the sphincter pupillae and ciliary muscles

Question 24

The trochlearnerve arises from thetrochlear nucleusof the brain at the level of the______________

• The trochlear nerve decussates within the ____________ before emerging on the contralateral side of the brainstem
• Emerging from the posterior aspect of it (the only cranial nerve to exit from the posterior midbrain)

Upon emerging from the dorsal surface of the brainstem the trochlear nerve curves around the brainstem in the _______________ and emerges between the posterior cerebral and superior cerebellar arteries (along with CN III fibers)

It runs anteriorly and inferiorly within thesubarachnoidspacebefore piercing the dura mater adjacent to theposterior clinoid processof the sphenoid bone
The nerve then moves along the lateral wall of thecavernous sinusinferior to the oculomotor nerve before entering the orbit of the eye viathesuperior orbital fissure to innervate the superior oblique muscle

Answer 24

inferior colliculus;

brainstem;

subarachnoid space

Question 25

The trochlearnerve arises from thetrochlear nucleusof the brain at the level of the______________

• The trochlear nerve decussates within the ____________ before emerging on the contralateral side of the brainstem
• Emerging from the posterior aspect of it (the only cranial nerve to exit from the posterior midbrain)

Upon emerging from the dorsal surface of the brainstem the trochlear nerve curves around the brainstem in the _______________ and emerges between the posterior cerebral and superior cerebellar arteries (along with CN III fibers)

It runs anteriorly and inferiorly; within the subarachnoidspacebefore piercing the dura mater adjacent to the_________________.

The nerve then moves along the _______________ of thecavernous sinusinferior to the oculomotor nerve before entering the orbit of the eye viathe______________ to innervate the superior oblique muscle

Answer 25

inferior colliculus;

brainstem;

subarachnoid space;

posterior clinoid processof the sphenoid bone;

lateral wall;

superior orbital fissure

Question 26

The abducens nerve arises from the abducens nucleus in the_________at the level of thefacial colliculus

• It exits the brainstem at the junction of the pons and the medulla
• It thenentersthe subarachnoid space and pierces the dura mater to travel in an area known as______________

At the tip of petrous temporal bone, the abducens nerve leaves Dorello’s canal and enters thecavernous sinus(a dural venous sinus)
- It travels through the cavernous sinus andenters the bony orbit via the ____________

Within the bony orbit, the abducens nerve terminates by innervating the__________

Answer 26

pons;

Dorello’s canal;

superior orbital fissure;

lateral rectusmuscle

Question 27

Ophthalmic division of Trigeminal Nerve

The trigeminal nerve originates fromfour nuclei, which extend from the midbrain to the medulla

• 3 sensory nuclei: ____________, _____________, _____________
• Motor nucleus of the trigeminal nerve

At the level of the______, the sensory nuclei merge to form a sensory root

• The motor nucleus continues to form a separate motor root
• These roots are analogous with the dorsal and ventral roots of the spinal cord

Within the_____________________, the sensory root expands into thetrigeminal ganglion
- The trigeminal ganglion islocated lateral to the cavernous sinus, in a depression of the temporal bone known as the______________

The motor root passes inferiorly to the sensory root, along the floor of the trigeminal cave
- Motor fibers are only distributed to the_______________

From the trigeminal ganglion, thethree terminal divisionsof the trigeminal nerve arise; theophthalmic (V1), maxillary (V2) and mandibular (V3) nerves.

The ophthalmic nerve travels laterally to the cavernous sinus and then exits the cranium via the_____________,where it divides into its three main branches: ______, _________, _________

Answer 27

Mesencephalic nucleus, Principle sensory nucleus, Spinal nucleus;

pons;

middle cranial fossa;

trigeminal caveor Meckel’s cave;

mandibular division(V3)

superior orbital fissure;

Frontal nerve, Lacrimal nerve, Nasociliarynerve

Question 28

Facial Nerve – to orbicularis oculi

The nerve arises in thepons, an area of the brainstem as two roots;

• A largemotor root
• And a smallsensory root(the part of the facial nerve that arises from the sensory root is sometimes known as the intermediate nerve)

The two roots travel through the _______________

• A 1cm long opening in the _________________
• Still within the temporal bone, the roots leave the internal acoustic meatus, and enter into the___________
• The canal is a ‘Z’ shaped structure

Within the facial canal, three important events occur:

• Firstly the two rootsfuseto form the facial nerve
• Next, the nerve forms the__________
• Lastly, the nerve gives rise to:
• -> Greater petrosal nerve- parasympathetic fibres to ___________________
• -> Nerve to stapedius–motor fibres to stapedius muscle of the middle ear
• -> Chorda tympani– special sensory fibres to the _____________ and parasympathetic fibres to the ____________________

The facial nerve then exits the facial canal via the ________________

• This is an exit located just posterior to the styloid process of the temporal bone
• It continues anteriorly and inferiorly into the _______ (the nerve terminates by splitting into five branches: ________________

Answer 28

internal acoustic meatus;

petrous part of thetemporal bone ;

facial canal;

geniculate ganglion;

mucous glands and lacrimal gland;

anterior 2/3 tongue;

submandibular and sublingual glands;

stylomastoid foramen;

parotid gland;

Temporal branch (supplies to orbicularis oculi), Zygomatic branch, Buccal branch, Mandibular branch, Cervical branch

Question 29

What are the attachments of the superior rectus?

Answer 29

Originates from the superior part of the common tendinous ring, and attaches to the superior and anterior aspect of the sclera

Question 30

What is the movement of the superior recti?

Answer 30

Main movement is elevation. Also contributes to adduction and intorsion of the eyeball

Question 31

What are the attachments of the inferior rectus?

Answer 31

Originates from the inferior part of the common tendinous ring, and attaches to the inferior and anterior aspect of the sclera

Question 32

What is the movement of the inferior recti?

Answer 32

Main movement is depression.Also contributes to adduction and extortion of the eyeball

Question 33

What are the attachments of the medial rectus?

Answer 33

Originates from the medial part of the common tendinous ring, and attaches to the anteromedial aspect of the sclera

Question 34

What is the movement of the medial recti?

Answer 34

Adducts the eyeball

Question 35

What are the attachments of the lateral rectus?

Answer 35

Originates from the lateral part of the common tendinous ring, and attaches to the anterolateral aspect of the sclera

Question 36

What is the movement of the lateral rectus?

Answer 36

Abducts the eyeball

Question 37

What is the attachments of the superior oblique?

Answer 37

Originates from the body of thesphenoidbone. Its tendon passes through a trochlear, and then attaches to the sclera of the eye, posterior to the superior rectus

Question 38

What are the actions of the superior oblique?

Answer 38

Depresses, abducts and intort the eyeball

Question 39

What is the attachments of the inferior oblique?

Answer 39

Originates from the anterior aspect of the orbital floor. Attaches to the sclera of the eye, posterior to the lateral rectus

Question 40

What are the actions of the inferior oblique?

Answer 40

Elevates, abducts and extorts the eyeball

Question 41

what is monocular eye movements called?

Answer 41

ductions

Question 42

what is binocular eye movements called?

Answer 42

versions or vergences

Question 43

what does version mean?

Answer 43

simultaneous movement of both eyes in the same direction

Question 44

what des vergence mean?

Answer 44

simultaneous movement of both eyes in the opposite direction i.e. convergence where there is simultaneous adduction (inward) movement in both eyes when viewing a near object

Question 45

what position is the lateral and medial recti best tested respectively?

Answer 45

abducted and adducted position

Question 46

what position is the superior and inferior recti best tested respectively?

Answer 46

elevation and depression respectively in the abducted position

Question 47

what position is the superior and inferior oblique best tested respectively?

Answer 47

elevation and depression respectively in the adducted position

Question 48

what is elevation of one eye called?

Answer 48

supraduction

Question 49

what is elevation of two eyes called?

Answer 49

supraversion

Question 50

what is depression of one eye called?

Answer 50

infraduction

Question 51

what is depression of two eyes called?

Answer 51

infraversion

Question 52

what is dextroversion?

Answer 52

Right Abduction

Left Adduction

Question 53

what is levoversion?

Answer 53

Right Adduction

Left Abduction

Question 54

what is torsion?

Answer 54

rotation of eye around the anterior-posterior axis of the eye

Question 55

[Levator Palpebrae Superioris]
The LPS is the only muscle involved in raising the superior eyelid.A small portion of this muscle contains a collection of smooth muscle fibres – known as the superior tarsal muscle. In contrast to the LPS, the superior tarsal muscle is innervated by the sympathetic nervous system

• Attachments:Originates from the _______________ , immediately above the optic foramen. It attaches to the superior tarsal plate of the upper eyelid
• Actions:Elevates the upper eyelid.
• Innervation:The levator palpebrae superioris is innervated by the_______________ . The superior tarsal muscle (located within the LPS) is innervated by the sympathetic nervous system.

Answer 55

lesser wing of thesphenoidbone;

oculomotor nerve(CN III)

Question 56

Orbicularis Oculi
The OO is the only muscle involved in closing the eye and consists of 3 parts: _________, ________, __________

Attachments:Originates from the nasal part of the_____________, from the frontal process of the____________ and themedial palpebral ligament. It attaches to the lateral palpebral ligament

Actions:The muscle acts to close the eye and is the only muscle capable of doing so. The palpebral portion acts involuntarily, closing the lids gently, as in blinking; the orbital portion is subject to conscious control. The lacrimal part of the orbicularis oculi also plays the function of a pump for tear drainage

Innervation:_________________

Answer 56

orbital, palpebral and the deeper lacrimal portion;

frontal bone; maxilla;

Facial nerve (CN VII)

Question 57

what are the 2 main types of eye movement disorders?

Answer 57

• Paralytic disorders (neurological)

- Restrictive disorders (restrictive)

Question 58

[3rd cranial nerve palsy]
Any damage to the 3rd nerve will cause weakness in the levator palpebrae superioris and all the extraocular muscles except the ____________

This will result in the patient having ptosis and the eye in a __________ position.

If the affected eye has a ________________ pupil, this is known as a surgical 3rd nerve palsy classically due to a brain aneurysm and can be life threatening

Answer 58

superior oblique and the lateral rectus;

“down and out”;

fixed and dilated;

Question 59

Another common nerve palsy to know is the 6th cranial nerve palsy. Damage to this nerve will cause weakness in the lateral rectus resulting in the patient being unable to ___________________

The most important etiologies that can cause a 6th nerve palsy include a “false localizing” 6th nerve palsy due to ______________, space occupying lesions like a nasopharyngeal carcinoma, ischemia and trauma

Answer 59

abduct the involved eye;

raised intracranial pressure

Question 60

Thyroid eye disease usually occurs in patients with hyperthyroidism

The most common form of hyperthyroidism is __________.

The recti muscles are affected in the acute stage by ________ and in the late stage by _____________.

It most commonly affects the ___________ then _________ then _________ then __________ recti

In the patient to the right, you can see that the right inferior recti is severely affected cause a ________________ in primary gaze and the inability to elevate the right globe due to restriction

Answer 60

Graves’ Disease;

inflammation ;

fibrosis and contracture;

inferior; medial; superior ; lateral;

right hypotropia

Question 61

The saccadic system exists to acquire a target of interest while exploring our visual world

Saccades are _________________ that are characterized by their ballistic nature and high velocity (400–800°/s)

These redirect our line of gaze while trying to acquire a new object of interest

For example, when visually scanning a room of people for a friend

Answer 61

rapid, brief conjugate eye movements

Question 62

Unlike the saccadic system, the smooth pursuit system kicks into action while ________________.

An apt example would be a watching a bird flying across the sky

The smooth pursuit system cannot follow objects moving faster than 30–40°/s

Faster moving objects elicit ___________.

Answer 62

tracking an object of interest that is in motion;

saccades

Question 63

[Corneal blink reflex]The corneal blink reflex is caused by a loop between the trigeminal sensory nerves and the facial motor nerve innervation of the orbicularis oculi muscles

The reflex activates when a sensory stimulus contacts either free nerve endings or mechanoreceptors within the epithelium of the cornea

Sensory information transmits through the _________________ of the trigeminal nerve (V) to synapse within the _________________ in the brainstem

The contacted nerve within the spinal trigeminal nucleus then projects to the ______________ and synapses with the facial nerve

The facial nerve exits the facial nucleus to activate the _____________ muscle
Contraction of this muscle causes a blink movement

Summary: Trigeminal (________________ branch) –> Spinal Trigeminal Nucleus –> RF –> Facial nucleus (bilaterally) –> Facial motor neurons (___________ branch) –> Orbicularis oculi

Answer 63

ophthalmic division;

spinal trigeminal nucleus;

facial nucleus;

orbicularis oculi;

nasociliary;

temporal

Question 64

[Lacrimation reflex]
Parasympathetic fibers that originates in __________________ and fibers leave brain with nervus intermedius and travel with CN VII through _____________, emerges from petrous portion of sphenoid bone as _______________; enters pterygoid canal and enters sphenopalatine ganglion, where primary parasympathetic fibers synapse and second-order fibers join ____________, which sends a branch to lacrimal gland

Summary: Trigeminal (____________branch) –> ________________ Nucleus –> RF –> Facial nucleus (bilaterally) –> Facial parasympathetic neurons –> Lacrimal gland

Answer 64

superior salivatory nucleus;

geniculate ganglion;

greater superficial petrosal nerve;

zygomatic nerve;

nasociliary;

Spinal Trigeminal

Question 65

The lacrimal system produces, distributes, and drains tears
Tears are produced by the lacrimal gland and multiple accessory glands
- The lacrimal gland is divided into the orbital lobe and the palpebral lobe by the ___________________
- The lacrimal gland is - oriented in the _____________ region of the orbit and lies in the __________________
- The ducts of the orbital lobe traverse the palpebral lobe before opening into the fornix

Tears are drained via a conduit of tubes along the medial angle of the eye

• The system is composed of paired lacrimal papillae, puncta, and canaliculi that connect to form the common canaliculus, lacrimal sac, and nasolacrimal duct
• The tears are stored in the ________________ and then drain through the nasolacrimal duct that opens into the ___________________

Answer 65

lateral horn of the levator aponeurosis;

superior-temporal ;

fossa glandular lacrimalis;

lacrimal sac;

inferior meatus of the nasal cavity

Question 66

[Lacrimal secretory system]

The lacrimal secretory system consist of the lacrimal gland and accessory glands

The main lacrimal gland is located in the superotemporal orbit in a shallow lacrimal fossa of the ________________.

The gland is divided by the lateral horn of the levator aponeurosis into a larger _____________, and a lesser _________________ below.

Two to six secretory ducts from the orbital lobe of the lacrimal gland pass through the palpebral lobe joining with ducts from the palpebral lobe to form six to 12 tubules that empty into the _____________________.

The lacrimal gland is responsible for the secretion of _________________ only.

Accessory lacrimal glands of Wolfring and Krause are located in the ________________ and maintain the ‘basal’ (unstimulated) tear secretion that is necessary to keep theeye moist.

Answer 66

frontal bone;

orbital lobe;

palpebral lobe;

superolateral conjunctival fornix;

‘reflex’ (aqueous) tears;

conjunctival fornices and along the superior tarsal border

Question 67

[Lacrimal drainage system]

The lacrimal excretory pathway begins as an opening on the medial portion of each eyelid termed the ___________.

The punctal opening widens into the __________, which is 2 mm in height and directed perpendicular to the eyelid margin, before making a sharp turn into the _______.

In more than 90% of individuals, the superior and inferior canaliculi merge to form a common canaliculus before entry into the ____________.

The nasolacrimal sac and duct are portions of the same continuous structure and it opens into the _____________.

Answer 67

punctum;

ampulla;

canaliculi;

nasolacrimal sac;

inferior meatus in the nasal passage

Question 68

[Tear film structure]

Thegoblet cells, the ______________ and _______________ contribute tothe inner mucus layer
- This helps to interface the tear film with the hydrophobic cornea and also contains IgA

The __________________ are responsible for the basalsecretion of the middle aqueous layer
- This layer provides nutrition to the cornea and assist in flushing out debris

The outer lipid layer is mainly produced by the __________________, but also by theglands of Zeis and the glands of Moll
- It is the outermost layer and acts to stabilize and prevent evaporation of the aqueous layer

Answer 68

tarsal crypts of Henlé;

limbal glands of Manz;

accessory lacrimal glands of Wolfring and Krause;

Meibomian glands

Question 69

The precorneal tear film has several important functions that are essential to the healthof the eye:
- lubricates the surface of the eye, facilitating the movement of the _____________
- maintains a _______________ surface on the cornea, to ensure that the eye cansee correctly
- provides the __________ , which has no blood vessels, with the nutrients and oxygennecessary for its metabolism
- contains enzymes (such as lysozyme), antibodies and phagocytic cells that destroybacteria and prevent the growth of microcysts of the cornea
removes waste products from the cornea

Answer 69

eyelids;

smooth refracting;

cornea