Eyes Flashcards
What are the structures which pass through the superior orbital fissure?
Lateral —-> Medial
Lacrimal nerve, Frontal nerve, Trochlear nerve, Superior branch of oculomotor nerve, Nasociliary nerve, Inferior branch of oculomotor nerve, Abducens nerve, Opthalmic veins, Sympathetic nerves
What is the optic chiasm?
X-shaped structure formed by two optic nerves, near the pituitary gland (some nerves cross over - contralateral - and some nerves continue - ipsilateral)
Describe the course of the optic nerve in the orbit.
Covered by meninges continuous with the brain which fuse with sclerae (infection spread)
Travel with central artery & vein of retina
What signs of raised intracranial pressure are present in the eyes?
- venous engorgement
- papilloedema = swelling of first part of optic nerve (optic disc/papilla), causing it to move to the centre
note: order of compression: optic nerve —> central vein of retina —> central artery of retina —> slow venous return —> oedema of retina
Describe the features of orbital fractures.
Usually occur at bony sutures on the medial & inferior walls of the orbit (thinner walls)
Medial wall fractured = can involve ethmoidal & sphenoidal sinuses
Inferior wall fractured = can involve maxillary sinus
Blowout fracture = displaces walls & contents
e.g. muscle entrapment, infection, diplopia (double vision)
- sinus can fill with fluid (oedema, blood, inflammatory infiltrate)
- enopthalmos (eye forced back into socket)
- infra-orbital bleeding
- pulsatile exopthalmos (blood forces eyeball forwards, which pulses in time with heartbeat)
What are the muscles responsible for eye movement?
LR6SO4R3
Lateral rectus (CNVI abducens nerve) = abduction of eyeball
Superior oblique (CNIV trochlear nerve) = pupil directs down & out
- primary action: intorsion (internal rotation)
- secondary action: depression in adducted position (reading a book)
- tertiary action: abduction
- test by asking patient to follow finger, which you move towards nose (looking inwards & downwards)
Rest of muscles (CNIII oculomotor nerve):
- levator palpebrae superioris = opens upper eyelid
- superior rectus = elevation, adduction, & internal rotation of eyeball
- medial rectus = adduction of eyeball
- inferior rectus = depression, adduction, & external rotation of eyeball
- inferior oblique = pupil directs up & out
+ orbicularis oculi (CNVII facial nerve) - lowers eyelid
+ superior tarsus - residual opening of eyelid
What clinical features related to the eye will result from a lesion of the third cranial nerve? What could cause this?
- loss of pupillary reflex on affected side
- eye turns down & out
- dilated pupil
- ptosis (paralysis of levator palpebrae superioris, but superior tarsus is still active but has little effect)
note: eyelid can not be raised voluntarily due to unopposed action of orbicularis oculi (CNVII facial nerve)
Possible causes: pressure from herniating uncus fracture involving cavernous sinus aneurysm
What clinical features related to the eye will result from a lesion of the fourth cranial nerve? What could cause this?
Inability to look down when the eye is adducted
Possible causes:
- stretching of nerve
- fracture of orbit
What clinical features related to the eye will result from a lesion of the sixth cranial nerve? What could cause this?
Eye fails to move laterally —> diplopia on lateral gaze & convergent strabismus (squint inwards)
Possible causes:
- base of brain lesion
- fracture involving orbit/cavernous sinus
What are the blood vessels of the orbit?
Opthalmic artery = branch of internal carotid artery, travels via the optic canal to give rise to central artery of retina and:
- short & long ciliary arteries —> external aspect of eye
- lacrimal artery —> lacrimal gland, eyelids, conjunctiva
- muscular branches —> extraocular muscles
- branches to ethmoidal & frontal sinuses, eyelids, forehead, scalp, etc.
note: lesser arterial supply to retina from infraorbital artery (branch of external carotid artery, via orbital floor)
Opthalmic veins =
- superior opthalmic veins move from inner angle of orbit, exiting via the superior orbital fissure
- inferior opthalmic veins move from plexus on floor & medial wall of orbit, exiting via the inferior orbital fissure
- give rise to the central vein of the retina before draining into the cavernous sinus
Blockage of central artery of retina —> rapid blindness
Blockage of central vein of retina —> slow, painless loss of vision
What are the purposes of the eyelids?
- protect from light & injury
- prevent corneal drying (which would cause infection/ulceration/scarring) by controlled spread of lacrimal fluid
- epithelial lining = conjunctiva (palpebral & ocular/bulbar)
note: palpebral fissure (distance between upper and lower eyelids) is often not equal (hereditary/ptosis)
Describe the anatomical features of the eyelid.
Levator palpebrae superioris
Orbicularis oculi (palpebral part)
Superior tarsal muscle = dense connective tissue containing tarsal glands (supportive function + residual opening of eyelids)
Tarsal (Meibomian) glands = secrete oil to prevent dry eyes
Ciliary glands = sebaceous; blockage of causes a stye (acute inflammation of gland causing pus-filled cyst to develop)
Palpebral conjunctiva
What are the triggers for reflex bilateral blinking?
- corneal drying
- corneal irritation (tiredness/irritants)
- corneal contact (perceived as pain)
- expectation of corneal contact
note: CNV1 = sensory component
CNVII = motor component
Outline the process of lacrimation.
Eyes close lateral to medial
Tears collect at lacrimal base (medial canthus)
Tear production is controlled by parasympathetic fibres of facial nerve (CNVII)
Sensory supply - lacrimal branch of CNV1 (also supplies eyelid and conjunctiva)
note: injury to the CNV1 —> sudden pain & excessive tears —> cornea at risk of abrasion/laceration due to foreign particles
Give some examples of age-related eye disorders.
Presbyopia = lens becomes harder & more flattened, reducing the focusing capacity
Cataract = partial/complete opacity of the lens
