anatomy of the orbit

Question 1

bones of orbit- what are vulnerable+ how many bones DIAGRAM

Answer 1

7 bones-maxilla quite thin, and ethmoid bone almost paper like- both vulnerable

Question 2

orbital foramina DIAGRAM

Answer 2

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

Question 3

extrinsic eye muscles- recti

Answer 3

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)

Question 4

extrinsic eye muscles- obliques

Answer 4

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

Question 5

extrinsic eye muscles- levator palpebrae superioris

Answer 5

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

Question 6

extrinsic muscles of eye DIAGRAM

Answer 6

most superior is levator

Question 7

isolated muscle actions DIAGRAM

Answer 7

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

Question 8

testing muscle actions clinically DIAGRAM

Answer 8

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

Question 9

nerves of orbit- superifical DIAGRAM

Answer 9

optic (retinal ganglion cells), oculomotor (motor to most eye muscles+ PNS), trochlear (SO) and abducens (LR) main branch of ophthalmic nerve is frontal nerve

Question 10

cavernous sinus+ relevance DIAGRAM

Answer 10

trochlear, oculomotor and 2 divisions of trigeminal here, along with abducens running with internal carotid- infection can damage nerves

Question 11

deeper nerves of orbit DIAGRAM

Answer 11

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)

Question 12

blood vessels of eye

Answer 12

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

Question 13

lacrimal system

Answer 13

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

Question 14

relations of orbit to cranial fossa and contents of orbit

Answer 14

INFERIOR to anterior cranial fossa, but ANTERIOR to middle cranial fossa contains eyeball (globe), extraocular muscles and lacrimal apparatus

Question 15

identify upper eyelid muscles and innervation

Answer 15

levator palpebrae superioris and ORBICULARIS OCULI innervated by facial nerve

Question 16

ophthalmic branch of trigeminal (v1) and branches DIAGRAM

Answer 16

purely sensory- divides into lacrimal, frontal and nasociliary nerves

Question 17

motor component of oculomotor and nerve route DIAGRAM

Answer 17

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

Question 18

pathway of SNS fibres

Answer 18

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

Question 19

importance of nasociliary nerve

Answer 19

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

Question 20

testing CN 3

Answer 20

movement of eyeball PNS functions ie light and accommodation reflex

Question 21

effects of damaged oculomotor

Answer 21

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)

Question 22

testing orbicularis oculi (facial) and ophthalmic branch of trigemnial

Answer 22

screw eyes shut for orbicularis test dermatome and corneal reflex for opthalmic

Question 23

pupillary light reflex

Answer 23

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

Question 24

corneal reflex

Answer 24

tests OPTHALMIC afferent- sensation to touch via ophthalmic efferent- facial nerve to orbicularis oculi to close eye

Question 25

lacrimal gland innervations

Answer 25

PNS fibres travel first in facial nerve- then branch off and synapse at PTERYGOPALATINE ganglion, then go along zygomaticotemporal nerve (V2), then lacrimal nerve of V1