Session 5 - Eyeball and Orbit Flashcards
(28 cards)
What are the main fissures and canals in the orbit canal and what runs through then?
Optic canal - optic nerve
Superior orbital canal - lacrimal, Trochlear, frontal, oculomotor and Abducens nerve and superior opthalmic vein.
Inferior orbital canal - infraorbital nerve
Fossa for lacrimal sac
What bones form the roof, floor and medial and lateral walls of the orbit?
Roof - Frontal bone, sphenoid bone
Floor - Zygomatic bone, maxillary bone
Medial - Nasal bone, Lacrimal bone, Maxillary bone
Lateral - Zygomatic bone, Sphenoid
Describe the structure of the optic nerve:
Optic nerve surrounded by pia, arachnoid and dura mater. These are continuous with the brain and could be a source of spread of infection.
Contains the central artery and vein.
What clinical sign would you see in the eyes if there is raised intracranial pressure?
Papilloedema
What areas of the orbit are more likely to be fractured?
Medial and inferior walls
What areas can be involved in fractures of the orbit?
Inferior wall fracture - maxillary sinus
Medial wall fracture - ethmoidal and sphenoidal sinus
What are the muscles of eye movements?
Superior, medial, lateral and inferior rectus muscles
Superior oblique and inferior oblique
Which nerves supplies the muscles of eye movement?
CN III Oculomotor nerve - Inferior oblique, medial, superior and inferior rectus.
CN IV - Trochlear nerve - Superior oblique
CV VI - Abducens nerve - Lateral rectus
What are the movements of the inferior oblique muscle?
Move eyes to look up and out
Abduction and extorsion (lateral rotation)
What is the action of the superior oblique?
Primary - intorsion - internal rotation
Secondary - depression in adducted position e.g. Reading a book
Tertiary - abduction
What is the blood supply to the orbit?
Opthalmic artery (branch of internal carotid)
Central artery branches off to supply the retina
If blocked causes blindness
What is the venous drainage of the orbit?
Superior and inferior orbital veins which exit via the supraorbital fissure and drain into the cavernous sinus.
The central vein of the retina either drains directly into the cavernous sinus or into the opthalmic veins.
Blindness occurs gradually and is slow and painless.
Infection can spread to the brain via the veins.
What are some of branches of the opthalmic artery?
Central retinal artery
Lacrimal artery
Posterior ciliary artery
Muscular branch of extraoccular arteries
What is the danger triangle?
An area where infections can spread from the face to the brain via the facial vein via the superior and inferior opthalmic veins to the cavernous sinus.
What are the consequences of spread of infection from the face to the brain?
Cavernous sinus thrombosis
Meningitis
Brain abscess
What is the purpose of the eyelids?
Protect the eye from light and injury
Prevent corneal drying, through controlled spread of lacrimal fluid
What are the layers of the eyelid?
Skin Areolar tissue Fibres of orbicularis oculi Levator palpebrae superioris Superior tarsus - dense connective tissue Tarsal glands - secrete oil (dry eye) Ciliary glands - sebaceous glands (stye) Palpebrae conjuctiva
What is the corneal reflex for?
Protects corneal drying out
In expectation of contact
Corneal irritation or contact (perceived as pain)
What nerves are involved in the blink reflex?
CN Vi - sensory
CN VII - motor action
What muscles are involved in closing the eyelids?
Orbicularis oculi
What muscles are involved in opening the eyelids?
Levator palpaebrae superioris
Superior tarsal muscles - smooth muscle of upper eyelid
How is the eye affected in Bells Palsy?
Paralysis of orbicularis oculi
Loss of corneal and blink reflex
Dry eyes
Likely lead to infection
What signs do you see in the eye if CNIII is paralysed?
Dropping of the upper eyelid ptosis
Only partial ptosis as superior tarsal muscle is still functional
What innervates the superior tarsal muscle?
Sympathetic fibres
