L42 - Orbit

Question 1

Define the bones that form the medial wall of the orbit?

Answer 1

Medial wall:

a. Frontal process of Maxilla
b. Lacrimal bone
c. Orbital plate of ethmoid
d. Body of sphenoid

Question 2

Bones that form the Inferior wall of orbit?

Answer 2

a. Medial part: Maxillary bone
b. Lateral part: Zygomatic bone
c. Posterior part: Palatine bone

Question 3

Bones that form the Lateral wall of orbit?

Answer 3

a. Anterior part: zygomatic bone

b. Posterior part: Greater wing of sphenoid

Question 4

Bones that form the Superior wall of orbit?

Answer 4

a. Anterior part: Frontal bone

b. Posterior part: Lesser wing of sphenoid

Question 5

Define the divisions of the orbital fissure?

Answer 5

• Divided into the superior and inferior orbital fissure

- Separated into 3 segments by the annulus of Zinn

Question 6

Which part of the orbit is most prone to blowout fracture?

Answer 6

posteromedial aspect of orbital floor (thin)

where infraorbital nerve passes through infraorbital foramen

Question 7

Which bone forms the orbital fissure?

Answer 7

Sphenoid bone

Question 8

Superior orbital fissure: Extraconal (outside annulus of Zinn) content?

Answer 8

 Lacrimal nerve (V1)
 Frontal nerve (V1): Supraorbital nerve Supratrochlear nerve

 Trochlear nerve (CN IV): superior oblique muscle
 Superior ophthalmic vein

Question 9

Intraconal (inside annulus of Zinn) superior orbital fissure content?

Answer 9

Nasociliary nerve (V1): branches:

• Infratrochlear nerve
• Long ciliary nerves
• Short ciliary nerves

Abducens nerve (CN VI): lateral rectus muscle

Oculomotor nerve (CN III):  Superior division 
 Inferior division

Question 10

Describe the origins of the Long and Short ciliary nerves?

Answer 10

 Long ciliary nerves (postsynaptic/postganglionic sympathetic fibers from superior cervical ganglion)

 Short ciliary nerves (postsynaptic parasympathetic fibers from oculomotor nerve, synapse at ciliary ganglion)

Question 11

The optic nerve passes through the superior orbital fissure inside the annulus of Zinn. T or F?

Answer 11

False

Inside annulus of Zinn but passes outside the sup. orbital fissure through optic canal

Question 12

Content of the Inferior orbital fissure?

Answer 12

Inferior ophthalmic vein

Maxillary nerve (V2) and branches:

• Zygomaticotemporal nerve
• Zygomaticofacial nerve
• Infraorbital nerve

Question 13

Which nerve passing through the orbital fissures cause numbness that radiate to teeth when damaged?

Answer 13

Infraorbital nerve (through inferior orbital fissure)

Question 14

Define the sensory nerve supply of the orbit?

Answer 14

Optic nerve: for vision

V1: superior orbital sensation, Upper eyelids

• Nasociliary n.
• Ant + post. Ethmoid,
• Frontal n.,
• Supraorbital n.
• Lacrimal n.

V2: inferior orbital sensation, lower eyelids

• Infraorbital nerve,
• zygomatic n.

Question 15

Motor supply of the orbit?

Answer 15

• CN III, IV, VI for Extraocular muscles
• CN III: opening of eyelids (levator palpebrae superioris)
• CN VII: for eye closure and brow movement.

Question 16

Define the blood supply to the anterior segment of the eyeball?

Answer 16

• Iris + ciliary body:
  Long Post ciliary artery (runs through the choroid) anastomose with Ant. Ciliary Artery (runs to anterior segment through extraocular muscles).
• Forms major and minor arterial circles on the iris

Question 17

Define what is supplied by the Long posterior ciliary artery?

Answer 17

Recurrent branches supply the choroid anterior to equator

Anastomose with Anterior ciliary artery and Short Posterior Ciliary artery

Question 18

Define what is supplied by short posterior ciliary artery?

Answer 18

Supply choroid posterior to equator + Optic disc

Question 19

Define what is supplied by Anterior ciliary artery?

Answer 19

7 arteries, 2 for each rectus muscle except Lateral Rectus (only 1)

Supply sclera, conjunctiva, iris

Question 20

Define the posterior arterial supply of the eyeball?

Answer 20

Retina: Central Retinal artery (runs along optic nerve)

Fovea avascular zone = no capillaries over fovea

Choroid:
- Short posterior ciliary artery (anastomose with long posterior ciliary a.)

Question 21

What forms the blood retinal barrier?

Answer 21

Tight junctions of the Retinal Pigmented epithelium

Separate choroidal and blood circulation = immune privileged site

Question 22

Venous drainage of eyeball?

Answer 22

Retina: Central retinal vein

Choroid: 4 vortex veins (2 on each side) Exit eyeball posterior to equator

• Superior Vortex + central retinal vein&raquo_space; superior Ophthalmic vein&raquo_space; supraorbital vein + facial v.
• Inferior vortex vein&raquo_space; inf. Ophthalmic v.&raquo_space; Ophthalmic v/pterygoid venous plexus/Cavernous sinus

Question 23

Define Hyphema

Answer 23

bleeding that fills the anterior segment of the eye

Question 24

Explain why Central retinal artery occlusion results in a Cherry red spot?

Answer 24

When the retinal circulation is occluded by a emboli, the choroidal circulation is unaffected

whole retina is pale because of a lack of retinal circulation. But the thinnest part at the fovea shows through as a “cherry red spot” of the underlying choroidal ciruclation

Question 25

List the cavities located around the orbit?

Answer 25

``` Superior = Anterior cranial fossa Medial = Nasal cavity and ethmoid air cells Inferior = Maxillary sinus Postero-Lateral = Middle cranial fossa ```

Question 26

Define the sinuses that lie medial to the orbit?

Answer 26

Anterior, middle and posterior ethmoid sinus Middle meatus

Question 27

List the nerves and arteries that pierce the medial orbit wall

Answer 27

Ant. and post. ethmoid nerve Infratrochlear n. Terminal branch of opthalmic artery

Question 28

List the sinuses that lie inferior to the orbit?

Answer 28

Maxillary and palatine sinus

Question 29

List the vessels and nerves that are found on the lateral wall of the orbit?

Answer 29

Lacrimal nerve and vessels | Zygomatic nerves and branches

Question 30

List the structures found at the superior wall of the orbit?

Answer 30

``` Periorbital fat Frontal nerve Trochlear nerve Levator Palpebrae superioris Superior rectus Superior oblique Lacrimal gland ```

Question 31

List the veins that drain the orbit?

Answer 31

Superior = Supratrochlear and Supra-orbital veins Medial = Opthalmic and angular v. Lateral = Superficial temporal v.

Question 32

Compare the action of the Superior and inferior oblique muscles?

Answer 32

obliques act opposite to their names + abduct Superior oblique: Intorsion, Depression , Abduction Inferior oblique: Extorsion, Elevation , Abduction

Question 33

List the actions of all the rectus musces?

Answer 33

MR - Adduction SR - Elevation, Adduction, Intorsion LR - abduction IR - Depression, Adduction, Extortion

Question 34

Role of suspensory ligaments of eyeball?

Answer 34

suspends the eyeball of the orbital space Act as fulcrum/ pulleys for extraocular muscles

Question 35

Function of eyelids?

Answer 35

- eyelashes to protect from dust, foreign body, and perspiration - To regularly spread tears and other secretions to keep the eye moist - Blink and menace reflex protect the eye from foreign body

Question 36

Compare asian with caucasion eyelids?

Answer 36

Asian: Lower lid crease Smaller tarsal plate (cartilage) Lower orbital fat 50% people have single lid crease

Question 37

Blood supply of eyelids?

Answer 37

Marginal and Peripheral/ Superior and inferior palpebral arterial arcades = anastomosis between the facial artery and branches + medial and lateral palpebral arteries

Question 38

Define the nerves that provide sensation to parts of the eyelids?

Answer 38

Superior eyelid = Supraorbtal and Supratrochlear Inferior eyelid = Infraorbital nerve

Question 39

Venous drainage of eyelids?

Answer 39

Superior and inferior palpebral veins Branches of the facial vein: angular, anterior facial (medial) Superficial temporal vein (lateral) Supraorbital and Supratrochlear veins (superior)

Question 40

Drainage of tears?

Answer 40

``` Superior and inferior puntum > Upper and Lower Lacrimal canaliculus > Common canaliculus > Lacrimal sac > Nasolacrimal duct > Opening of nasolacrimal duct into Inferior nasal meatus ```

Question 41

What maintains tears from quickly evapourating?

Answer 41

Meibomian glands at the lid margin makes meibom to prevent tears from quickly evaporating

Question 42

Pathogenesis of Dacrocystitis?

Answer 42

Dacrocystitis occurs when the Nasolacrimal duct is blocked. Bacteria infect