The Orbit and Eyeball

Question 1

Name the layers of the eyelid

Answer 1

Skin
Areolar tissue
Orbicularis oculi fibres
LPS muscle
ST muscle
Tarsal glands
Ciliary glands 
Conjunctiva

Question 2

Describe some of the functions of the eyelid

Answer 2

Protect from light and injury

Prevent corneal drying through controlled spread of lacrimal fluid

Question 3

List the muscles of eye movement and their innervation

Answer 3

4 recti - superior, inferior, lateral, medial
2 oblique - superior, inferior
Arise from common tendinous ring
All innervated by CN III except lateral rectus (CN VI) and superior oblique (CN IV)

Question 4

Describe the blood vessels of the orbit

Answer 4

Arteries:
Ophthalmic artery –> central artery of the retina (internal carotid)
Branches - lacrimal, posterior ciliary
Infraorbital artery (external carotid)
Veins:
Superior and inferior ophthalmic veins –> cavernous sinus
Central vein of the retina –> cavernous sinus/ophthalmic veins
Infraorbital vein –> pterygoid venous plexus

Question 5

Describe cases and consequences of damage or disorders affecting the orbit and orbital contents

Answer 5

Fractures of the orbit - medial and inferior walls thin –> blowout fracture that displaces wall and contents –> infection, diplopia, enopthalmus, infraorbital bleeding, pulsatile exopthalmos
Conjunctivitis
Horner’s syndrome - damage to sympathetic trunk –> partial ptosis, miosis, enopthalmus, anhidrosis
Bell’s palsy - facial nerve palsy –> failure to close eye, loss of blink and corneal reflex, dry eyes
Blockage of artery - sudden blindness
Blockage of vein - slow, painless loss of vision
Danger triangle - communication between facial vein and cavernous sinus via ophthalmic veins –> cavernous sinus thrombosis, meningitis, brain abscess
Papilloedema –> increased intracranial pressure, backflow of venous blood, increased fluid, pushes optic disk forward

Question 6

List the bones of the orbit

Answer 6

Roof - frontal, sphenoid
Floor - zygomatic, maxilla
Medial - ethmoid, maxilla, lacrimal
Lateral - zygomatic, sphenoid

Question 7

Which structures run through the superior orbital fissure?

Answer 7

CN III, IV, V1, VI
Lacrimal (V1)
Frontal (V1)
Trochlear
Superior oculomotor
Nasociliary (V1)
Inferior oculomotor
Abducens

Question 8

Which structures run through the inferior orbital fissure?

Answer 8

CN V2
Emissary veins (inferior opthalmic vein –> pterygoid venous plexus)
Infraorbital vessels

Question 9

Which structures run through the optic canal?

Answer 9

Optic nerve

Opthalmic artery

Question 10

What is the nerve supply to the cornea?

Answer 10

V1

Question 11

Explain the difference between partial and complete ptosis with regards to the neural innervation of the eyelid

Answer 11

Partial - damage to CN III (levator palpebrae superioris)

Complete - complete damage to CN III (oculomotor nerve proper (LPS + superior tarsals (sympathetics))

Question 12

Describe the direct and consensual light reflex

Answer 12

Light –> optic nerve –> pre-tectal nucleus (midbrain) –> edinger westphal nucleus –> ciliary ganglion
Pretectal nucleus gives bilateral innervation

Question 13

Describe the structure and function of the lacrimal apparatus

Answer 13

Lacrimal gland –> lacrimal gland ducts –> punchum (x2) –> lacimal canal –> lacrimal sac –> nasolacrimal duct –> posterior nasal meatus