anatomy of the orbit Flashcards
bones of orbit- what are vulnerable+ how many bones DIAGRAM
7 bones-maxilla quite thin, and ethmoid bone almost paper like- both vulnerable
orbital foramina DIAGRAM
optic canal- optic nerve (2) and opthalmic artery (main vessel to eye) in lesser wing of sphenoid inferior orbital fissure- maxillary nerve (v2) with infraorbital vessels, which emerge from hole not labelled (infraorbital foramen) superior orbital fissure- all nerves innervating extrinsic muscle of eye (oculomotor 3, trochlear 4 and abducens 6, and opthalmic nerve V1) + SNS fibres+ opthalmic vessels
extrinsic eye muscles- recti
4 recti muscles inferior, superior, medial and rectal, which originate at COMMON TENDINOUS RING, and insert at SCLERA, supplied by oculomotor except lateral muscle (abducens)
extrinsic eye muscles- obliques
2 oblique inferior and superior, which originate at maxilla and common tendinous ring respectively, and insert at POST/INFERIOR QUADRANT and POST/SUP VIA TROCHLEA (bony structure) respectively, innervated by oculomotor and trochlear nerve respectively
extrinsic eye muscles- levator palpebrae superioris
muscle of upper eyeld, originating from lesser wing of sphenoid, and inserting at superior tarsal plate+skin of eyelid innervated by oculomotor and SNS fibres to smooth muscle (IMPORTANT- if SNS innervation lost to HNS= horners syndrome= drooping upper eyelid
extrinsic muscles of eye DIAGRAM
most superior is levator
isolated muscle actions DIAGRAM
LR and MR purely ab/adduct, SI/IO move eye up/down and abduct, SR/IR move eye up/down and adduct- ONLY IF ISOLATED, doesn’t actually occur clinically
testing muscle actions clinically DIAGRAM
LR and MR simple- depression/elevation of eye doesn’t isolate any muscle as two muscles help for each although anatomically SO moves down and out, to test it it you need to move down and IN, and vice versa for IR- IMPORTANT and CONFUSING
nerves of orbit- superifical DIAGRAM
optic (retinal ganglion cells), oculomotor (motor to most eye muscles+ PNS), trochlear (SO) and abducens (LR) main branch of ophthalmic nerve is frontal nerve
cavernous sinus+ relevance DIAGRAM
trochlear, oculomotor and 2 divisions of trigeminal here, along with abducens running with internal carotid- infection can damage nerves
deeper nerves of orbit DIAGRAM
opthalmic branches- lacrimal (to gland), frontal (supraorbital branch runs to forehead ie when testing trigeminal at forehead, ur testing this branch), and supratrochlear branch), and nasociliary branch (ethmoidal branch, infratrochlear branch and branch to ciliary ganglion ciliary ganglion- PNS to sphincter pupillae and ciliary muscle: arising from this is post ganglionic fibres (short ciliary nerves)
blood vessels of eye
opthalmic artery- supplies retina, muscles, ciliary branch, lacrimal etc opthalmic veins are superior (go to cavernous sinus ie can potential route of intracranial infection) and inferior- inferior goes through inferior orbital fissure to join pterygoid plexus
lacrimal system
lacrimal gland supplied PARASYMPATHETICALLY via facial nerve- goes into lacrimal sac, then into inferior meatus via nasolacrimal duct IMPORTANT- lacrimal nerve branch of V1, but facial nerve PNS fibres from pterygopalatine ganglion HITCHHIKES ONTO lacrimal nerve to travel to gland
relations of orbit to cranial fossa and contents of orbit
INFERIOR to anterior cranial fossa, but ANTERIOR to middle cranial fossa contains eyeball (globe), extraocular muscles and lacrimal apparatus
identify upper eyelid muscles and innervation
levator palpebrae superioris and ORBICULARIS OCULI innervated by facial nerve
ophthalmic branch of trigeminal (v1) and branches DIAGRAM
purely sensory- divides into lacrimal, frontal and nasociliary nerves
motor component of oculomotor and nerve route DIAGRAM
motor to eye muscles, and PNS motor to spinchter pupillae+ ciliary body nerve divides into superior and inferior divisions, THEN enter orbit through common tendinous ring (PNS component in INFERIOR division)- fibres go to ciliary ganglion, then to body and pupillae via ciliary nerve WITH T1 SNS FIBRES
pathway of SNS fibres
originate at T1, synapse and superior cervical ganglion (C2), then go to carotid plexus, where they go to dilator pupillae (with CILIARY NERVES), blood vessels of eye and SUPERIOR TARSAL MUSCLe
importance of nasociliary nerve
this nerve has ciliary branches- oculomotor PNS fibres travel to ciliary ganglion, then leave oculomotor and HITCHHIKE onto ciliary branches of V1 to go to pupillae and body also, SNS fibres HITCHHIKE onto ciliary branches of nasociliary nerve to go to dilator pupillae and blood vessels of eye
testing CN 3
movement of eyeball PNS functions ie light and accommodation reflex
effects of damaged oculomotor
loss of movement of MOST ocular muscles PTOSIS (drooping eyelid due to levator muscle) loss of PNS function= dilated pupil (NOT SNS at hitchhikes onto V1)
testing orbicularis oculi (facial) and ophthalmic branch of trigemnial
screw eyes shut for orbicularis test dermatome and corneal reflex for opthalmic
pupillary light reflex
affterent- impulses travel along optic nerve via left and right optic tracts to PRETECTAL nucleus, then BOTH EDINGER WESTPHAL nuclei efferent- PNS fibres travel via inferior branch of nerve 3, synapse in ciliary ganglion, then via ciliary nerve to BOTH sphincter pupillae (ie ipsilateral and CONSENSUAL response) this means if damage in AFFERENT PATHWAY, when light shined on undamaged eye, both pupils constrict due to consensual response, but when light shone on damage eye, no afferent response, so BOTH EYES dilate
corneal reflex
tests OPTHALMIC afferent- sensation to touch via ophthalmic efferent- facial nerve to orbicularis oculi to close eye
