Sem 2 - W - Orbit - Bones of Orbit, Tarsal Plates, Ligaments, Eyeball, Intra/extraocular muscles, nerves/vessels, lacrimal gland

Question 1

What bone forms the inferolateral margin of the orbit? What bone forms the inferomedial margin of the orbit? What bone forms the superior margin of the orbit?

Answer 1

• INferolateral margin of the orbit - zygomatic bone
• Inferomedial margin of the orbit - maxillary bone
• Superior margin of the orbit - frontal bone

Question 2

Forming the posterior bones of the orbit What is the order from medial to lateral? State the ducts/foramin in the bones

Answer 2

• Lacimal bone with nasolacrimal duct
• Ethmoid bone
• Sphenoid bone with optic canal medially and superior obital fissure more lateral

Question 3

There is a small contribution from the palatine bone in the orbit Where is this contribution?

Answer 3

The palatine bone offers a small contribution to the floor of the orbit in the wall of the inferior orbital fissure

Question 4

What is the function of the tarsal plates? Which part of the obicularis oculi is associated withtthe tarsal plates?

Answer 4

The palpebral part (gentle blinking) of the obricularis oculi is associated with the tarsal plates

• The tarsal plates are dense connective tissue which supports the eyelids and contain glands

Question 5

How are the tasral plates attached to the orbit?

Answer 5

The tasral plates are attached to the orbit by the medial and lateral palpebral ligaments

• Medial palpebral ligament - attaches to the maxilla
• Lateral palpebral ligament attaches to the zygoma

Question 6

What do the tarsal glands produce and what is the function of this? What is the other name for the tarsal glands?

Answer 6

The tarsal glands produce meibum (meibomian glands)

• An oily substance which prevents the evaporation of tears

Question 7

What is the function of the suspensory ligament of the eyeball? What does it run between and what muscles does it close?

Answer 7

The suspensory ligament of the eye forms a hammock stretching below the eye from medial to lateral check ligament and enclosing the inferior rectus and inferior oblique muscle It acts to support the eyeball

Question 8

What is the function of the medial and lateral check ligaments?

Answer 8

The medial and lateral check ligaments are expansions of the medial and lateral recti muscle sheaths respectively which act to restrict the movements of the medial and lateral recti muscles respectively

Question 9

What are the three layers of the eye? Which is the tough outer fibrous coat of the eye? Which is the vascular layer? Which is the neuronal layer?

Answer 9

Three layers of the eye

• Outer tough fibrous coat of the eye - sclera with the cornea anteriorly (transparent)
• Middle vascular layer - uvea (choroid, ciliary body and iris)
• Inner neuronal layer - retina

Question 10

There are two types of photoreceptors in the human retina, rods and cones. Rods are responsible for vision at low light levels but are not capable of colour vision Cones are active at higher light levels and are capable of colour vision

• * Where are cones in the highest density?
• * Which is more useful for peripheral vision?
• * What is the optic disc?

Answer 10

• Cones are found in their highest density at the muscula lutea (the fovea) and are used for central vision
• Rods are found on the circumference of the retina and are useful for peripheral vision
• The optic disc is where the optic nerve leaves the eye

Question 11

Aqueous humor is found in the anterior and posterior chambers of the eye

• Where are these chambers and how does aqueous humor reach them?
• What produces the aqueous humor?

Answer 11

The aqueous humos is produced by ciliary body filtering blood

• The posterior chamber is found posterior to the iris between the lens and ciliary body, the fluid drains through the pupil and into the anterior chamber The anterior chamber of the eye is between the iris and the cornea

Question 12

What is the function of the aqueous humour? Where does it drain to?

Answer 12

The aqueous humour functions to help maintain intraocular pressure It drains via the trabecular meshowrk into the corneo-scleral junction in the canal of Schlemm and back into the venous system

Question 13

What is the transparent jelly like substance posterior to the lens known as? What is its function?

Answer 13

The vitreous humor is a transparent like jelly substance posterior to the lens that helps to support the retina

Question 14

Intraocular eye muscles

• * Dilator pupillae
• * Sphincter (constrictor) pupillae
• * Ciliary muscles (ciliary body)

What is the function of the dilator and sphincter pupillae and what are they innervated by?

What is the difference in the arrangement of the muscle fibres?

Answer 14

Dilator pupillae is innervated by sympathetics carried on blood vessels, it increases the diameter of the pupil - has radially arrange smooth muscle fibres

Sphincter pupillae is innervated by parasympathetics carried by the oculomotor nerve, it decreases the diameter of the pupil, has circularly arranged smooth muscle fibres

Question 15

Intraocular eye muscles

• Dilator pupillae
• Sphincter (constrictor) pupillae
• Ciliary muscles (ciliary body)

What do the sympathetic fibres travel on to reach the dilator pupillae?

Answer 15

The sympathetic fibres travel up the ICA and then along the ophthalmic artery to reach the dilator pupillae of the lens

Question 16

• What innervates the ciliary muscles to enable them contract?
• What attaches the ciliary muscles to the lens?

Answer 16

• The ciliary muscles are innervated by parasympathetics via the oculomotor nerve (CN III)
• The ciliary muscles are attached to the lens by the zonular fibres
• The ciliary muscles is a circular muscle around the lens

Question 17

What happens to the lens when the ciliary muscles relax or contract?

• State when the lens is better for near or distant vision

Answer 17

When the ciliary muscles relax, this causes the zonular fibres to tighten (under tension) therefore stretching the lens making it flatter for distant vision When the ciliary muscles contract, the zonular fibres relax therefore the lens is able to bulge making it more spherical to retract near vision onto the retina

Question 18

What is the process known as where the intrinsic eye muscle change the shape of the lens to enable focus on an image?

Answer 18

This is known as accommodation

Question 19

What are the extraocular muscles?

Answer 19

• * Levator palpebrae superioris
• * Superior oblique
• * Inferior oblique
• * Superior rectus
• * Medial rectus
• * Inferior rectus
• * Lateral rectus

Question 20

What is different about superior oblique and superior rectus compared to the inferior oblique and inferior rectus

Answer 20

The superior oblique passes under the superior rectus to attach to the sclera of the eye The inferior oblqiue passes over the inferior rectus to attach to the sclera of the eye

Question 21

What are the attachments of the 7 extraocular muscles? Do the recti or obliques attach anterior to the equator of the eye?

Answer 21

• Levator palpebrae superioris from obrital roof to the upper eyelid
• Superior, medial, inferior & lateral rectus attach from annular ring to the sclera anterior to the equator
• Superior oblique attaches from the lesser wing of the sphenoid & inferior oblique from the orbital floor to insert onto the sclera posterior to the equator

Question 22

What part of the sphenoid bone do the superior orbital fissure and optic canal sit between?

Answer 22

• The superior orbital fissure sits between the greater and lesser wings of the sphenoid bone
• The optic canal sits between the lesser wing and body of the sphenoid bone

Question 23

What allows the eyes to move in more than one direction in the orbit?

Answer 23

The axes of the orbit (bony cavity) and the optical axis (line of gaze) are different and therefore the eye muscles can move the eye in more than one direction

Question 24

Mneomic to help remember the basic movements of the extraocular muscles is RADSIN What is the nerve supply to each extraocular muscle?

Answer 24

RAD-SIN

• Rectus generally ADdduct (therefore obliques must abduct)
• Superior (rectus + oblique) INtort (therefore inferior (rectus + oblique) must extort)
• LPS, SR, IR, MR, IO - Oculomotor
• Lateral rectus - abducent
• Superior oblique - trochlear

Question 25

State the full function of each of the extraocular muscles State their main movement first for the muscles with more than one movement

Answer 25

• LPS - raises upper eyelid
• Superior rectus - elevation , adduction, intorsion
• Inferior rectus- depression , adduction, extortion
• Medial rectus - adduction
• Lateral rectus - abduction
• Superior oblique- intorsion , depression, abduction
• Inferior oblique - extorsion, elevation, abduction

Question 26

Now state each extraocular muscle attachment, function and nerve supply * RAD-SIN * Rectus generally ADdduct (therefore obliques must abduct) * Superior (rectus + oblique) INtort * (therefore inferior (rectus + oblique) must extort)

Answer 26

• * LPS - Attaches from orbit roof to upper eyelid, raises upper eyelid, CN III
• RECTI attach from annular ring to cornea anterior to equator
  
  • * SR - elevation , adduction, intorsion, CN III
  • * IR - depression , adduction, extorsion, CN III
  • * MR - adduction, CN III
  • * LR - abduction, CN VI
• Superior oblique - lesser wing of sphenoid to cornea posterior to the equator - intorsion , depression, abduction, CN IV
• Inferior oblique - orbital floor to cornea posterior to the equator - extorsion , elevation, abduction, CN III

Question 27

Where does the optic nerve begin? What % of fibres travel through the thalamus? Once the fibres reach the thalamus, what are the optic fibres known as that head towards the primary visual cortex? Where is the primary visual cortex?

Answer 27

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Question 28

After passing through the superior orbital fissure the oculomotor nerve will divided into a superior and an inferior division What muscles specifically does each division supply? Which division travels to the ciliary ganglion and why?

Answer 28

• Superior division supplies the superior rectus and levator palpebrae superioris
• The inferior division supplies the medial rectus, inferior oblique and inferior rectus and travels to the ciliary ganglion where it picks up parasympathetics

Question 29

What are the nerve branches which come from the ciliary ganglion carrying parasympathetics to the sphincter pupillae and ciliary muscles known as?

Answer 29

The postganglionic fibres run in short ciliary nerves to supply the ciliary muscles and sphincter pupillae with parasympathetic innervation

Question 30

If we were to take off the frontal bone (roof of the orbit), we would be able to see the trigeminal nerve branches superiorly from CN V1 What are the 3 branches of CN V1? Which branch passes through the annular ring?

Answer 30

Ophthalmic nerve divides into

• Frontal nerve - most superiorly
• Nasociliary nerve medially (passes through the annular ring)
• Lacrimal nerve laterally

The nerve medial to the frontal nerve in this diagram is the trochlear nerve

Question 31

What two divisions does the frontal nerve give anteriorly? How do these branches exit the orbit?

Answer 31

Frontal nerve gives off supraorbital and supratrochlear nerve

• Supraorbital nerve exits the orbit through the supraorbital foramen
• Supratrochlear nerve exits the orbit between the pulley (trochlea) of the superior oblique and the supraorbital foramen

Question 32

What does the lacrimal nerve supply? What branches does the nasociliary nerve give (PLICA)?

Answer 32

Lacrimal nerve provides geeral sensory to the lacrimal gland

Nasociliary nerve branches

• * Posterior ethmoidal nerve
• * Long ciliary nerve
• * Infratrochlear nerve
• * Communicating sensory branch to ciliary ganglion
• * Anterior ethmoidal nerve

Question 33

What runs through the optic canal with the optic nerve?

What branches does this give to the face/scalp, naspharynx, lacrimal gland, the retina?

Answer 33

Ophthalmic artery runs through the optic canal with the optic nerve giving the central artery of the retina to run to the retina

• It gives the supraorbital artery and terminates as the dorsal nasal and supratrochlear arteries which supply face/scalp.
• It gives the anterior /posterior ethmoidal arteries which pass into the nasopharynx
• It gives the lacrimal artery to the lacrimal gland.

Question 34

What is the route of infection from forehead/face to the dural venous sinuses?

Answer 34

Blood can drain back from the forehead via the supraorbital and supratrochlear veins into the superior ophthalmic vein into the cavernous dural venous sinus

Blood can drain back from the face into the pterygoid and cavernous dural venous sinus

Question 35

Lacrimal gland has tiny small ducts which secrete tears to eye to protect it

Describe the drainage of these tears all the way to the nasopharynx

Answer 35

There are tiny punctum at the medial corner of the eye which absorbs these tears into canaliculi which drain into the lacrimal sac

This continues as the nasolcarimal duct which empties into the inferior nasal meatus in the lateral wall of the nasal cavity