anatomy Flashcards
what are some anatomical features of the orbit?
supraorbital notch / foramen
orbital plate of ethmoid
infraorbital foramen
superior orbital fissure
optic canal
orbital plate of frontal
which bones make up the orbit?
frontal
zygomatic
maxilla
palentine
sphenoid
ethmoid
lacrimal
what shape is the orbit?
pyramidal
the base is located anteriorly
and the apex is located at the optic canal
which way does the orbit face?
anterolaterally
which bones in the orbit are susceptible to fracture?
orbital plate of ethmoid and maxilla
what is the most external structure of the eyelid?
orbicularis oculi muscle
what is the orbicularis made up of?
the orbital part- responsible for tight squeezing shut of eyes
the palpebral part- responsible for gentle closing of eyelid
what nerve innervates the orbicularis oculi?
CN VII
what helps prevent spread of infection between the deep and superficial eyelid?
the orbital septum
what makes up the deeper eyelid?
lateral palpebral ligament
superior tarsus
inferior tarsus
medial palpebral ligament
tendon of LPS
what kind of muscle is tenon of levator palpebrae superiorus?
skeletal mainly
bit of smooth (superior tarsus muscle/ muellers muscle)- sympathetic innervation
what do tarsal glands secrete?
lipids
where is the lacrimal gland found?
superiolaterally
which nerve innervates production of lacrimal fluid?
CN VII (parasympathetic)
what is the route of lacrimal fluid?
- wash over eye
- pushed towards medial angle
- drains through lacrimal puncta
- eventually reaches inferior meatus
name the seven extraocular skeletal muscles?
superior rectus
inferior rectus
medial rectus
lateral rectus
superior oblique
inferior oblique
LPS
what are the attachments for the rectus muscles?
- all originate from common tendinous ring
- all insert onto sclera
what are the attachments for oblique muscles?
superior oblique
- originates from sphenoid bone
inferior oblique
- originates from orbital plate of maxilla
both insert onto sclera
what is the attachment for LPS?
originates from lesser wing of sphenoid
inserts onto skin and tarsus of superior
eyelid
what is the innervation for extraocular muscles?
LR6 SO4 AO3
lateral rectus CN VI (abducent nerve)
Superior oblique CN IV (trochlear nerve)
All others CN III (oculomotor nerve)
what are the features of the fibrous layer of the eye?
outer layer
2 parts
:sclera – muscle attachment
:cornea – 2/3 of refractive power
what are the features of the uvea (vascular layer) of the eye?
middle layer
3 parts
:iris – pupil diameter
:ciliary body – controls iris, shape of lens and secretion of aqueous humour
:choroid – nutrition and gas exchange
what are the features of the retinal (photosensitive) layer of the eye?
inner area with many parts
what are the features of the anterior segment of the eye?
in front of lens (cornea to iris)
has an anterior chamber and a posterior chamber (iris to vitreous body)
contains aqueous humour
what are the features of the posterior segment of the eye?
behind lens
2/3rds of eye
contains vitreous body which contains vitreous humour
which structure of the eye is completely avascular?
cornea
what is the pathway of circulation of aqueous humour?
Ciliary body
-smooth muscle and blood vessels
-ciliary processes secrete aqueous
- Aqueous circulates
-within posterior chamber
-nourishes lens - Aqueous then passes through pupil
-into anterior chamber
-nourishes cornea - Aqueous reabsorbed
-into scleral venous sinus (Canal of Schlemm)
-at iridocorneal angle
what can cause ischaemia of the retina and glaucoma?
raised intra ocular pressure
which sinus does the internal carotid pass through?
cavernous artery
What does the ophthalmic artery pass through?
The optic canal, travelling with the optic nerve
What supplies the uvea (coroid)?
Ciliary arteries
What do ciliary arteries pierce through?
Optic nerve
What is the only blood supply to the retina?
Central blood supply to the retina
What is the valveless vein?
Facial vein
What are the bits of the retina?
Fundus
Optic disc
Macula
Fovea
What are the features of the fundus?
Posterior area where light is focused
Contains the optic disc, macula and fovea
What are the features of the optic disc?
Point of CN II formation
Only point of entry/exit for blood vessels and axons of CN II
blind spot
What are the features of the macula?
Greatest density of cones
What are the features of the fovea?
Centre of the macula
A depression (1.5 mum diametre)
Area of most acute vision
Where do the retina veins and arteries lie?
Anterior to the retina
Are there photoreceptors in the optic disc?
No
What does a complete interruption of the retinal artery branch/retinal vein lead to?
Loss of an area of visual field corresponding to the area of ischaemia
What does a complete interruption of flow of the central artery lead to?
Monocular blindness (complete blindness)
What does the vertical axis of the eye control?
Abduction/addiction
Direction of gaze
What does the transverse axis of the eye control?
Elevation/depression
Direction of gaze
What does the anteroposterior axis control?
Intorsion/extortion (medial/lateral)
Superior pole of the eyeball
Is the axis of the orbit the same as the axis of the pupillary gaze?
No
When testing the muscle what else is being tested?
Nerve supply
What does the lateral rectus do?
Only abducts eyeball
Supplied by CN VI (abducent)
Brings pupillary gaze into same plane as superior rectus and inferior rectus
What does superior rectus do?
When in abduction (done by lateral rectus), SR can only elevate
Supplied by CN III (oculomotor)
What does inferior rectus do?
When in abduction (lateral rectus) IR can only depress
Supplied by CN III (oculomotor)
What does medial rectus do?
Only adducts eyeball
CN III (oculomotor)
Brings line of gaze into the same plane as superior oblique and inferior oblique attachments
What does inferior oblique do?
When in adduction (medial rectus) IO can only elevate
Supplied by CN III (oculomotor)
What does superior oblique do?
When in adduction (medial rectus) SO can only depress
Supplied by CN IV (trochlear)
What does CN V1 (opthalamic nerve) innervate?
Upper eye lid
Cornea
Conjunctiva
What does CN V2 (maxillary nerve) innervate?
Skin of lower eyelid
Skin over maxilla
What are the features of corneal (blink) innervations
Sensory (affferent) limb
-action potentials conducted from cornea via CN V1 branches
Then goes to trigeminal ganglion then along CN V to the pons
There is a central CNS connection between CN V and CN VII
motor (efferent) limb
- APs conducted via CN VII to the eyelid part of orbicularis oculi
What are the autonomic reflexes of the eye
Wide opening of flight or fight
Pupillary light reflex
Accommodation reflex
Lacrimation reflex
Vestibule-ocular reflex
Oculocardiac reflex
What are the features of vestibuloocular reflex?
Turns eye in opposite direction to head movement
Stabilises gaze during movement
CNS connections between CN VIII and III, IV and VI
What does the sympathetic reflex do?
Opens eyes wider
Gets more light into eyes
Focus on far objects
Emotional lacrimation
what are the parasympathetic reflexes of the eye?
gets less light into eye
focuses on near objects
reflex lacrimation (to clear foreign bodies etc)
what opens eyes wider?
levator palpebrae superioris
contains skeletal muscle PLUS smooth muscle
Mueller’s muscle
sympathetic innervation
which route do the parasympathetic fibres to open the eye wider travel?
superior cervical sympathetic ganglion
then
internal carotid nerve
then
internal carotid plexus
then
axons carried on the ophthalmic artery…
and on its branches to the orbital structures
what do sphincter pupillae fibres do?
constrict the pupil
- in bright light and “rest & digest”
sphincter pupillae fibres encircle pupil around the internal circumference of iris
what is the innervation of phincter pupillae fibres?
parasympathetic
what are the features of dilator pupillae fibres?
dilator pupillae fibres are radially arranged
originate around the external circumference of iris – fixed
insert around the internal circumference of iris - mobile
what is the innervation of dilator pupillae fibres?
sympathetic
what are the features of the pupillary light reflex?
special sensory (afferent) limb of the reflex is the ipsilateral CN II
CNS connections occur in the midbrain
motor (efferent) limb of the reflex is bilateral via CNs III
direct light reflex occurs in the stimulated eye
a consensual light reflex occurs in the non-stimulated eye
what happens to the ciliary muscle in ‘far’ vision?
it relaxes:
no parasympathetics
ligament tightens & lens flattens to focus on an object in the distance
what happens to the ciliary muscle in ‘near’ vision?
it contracts:
parasympathetic
ligament relaxes & lens becomes spherical to focus on near objects
what are the features of basal tears?
corneal health
clean/nourish & hydrate the avascular cornea
contain lysozyme
- hydrolyses bacterial cell walls
what are the features of reflex tears?
extra tears in response to mechanical or chemical stimulation
afferent limb is CN V1 from cornea/conjunctiva
efferent limb is parasympathetic axons originating from CN VII
what is the term for a droopy eyelid?
ptosis
