Anatomy Flashcards
how is the eye protected from a direct blow
the superior orbital margin is more anterior than inferior orbital margin
what is commonly affected by orbital blowout fractures and why
medial wall and orbital floor
very thin
what can be damaged in a blowout fracture
orbital contents can become trapped
infraorbital NVB can be damaged
what is the external layer of the eyelid made of
orbicularis oculi
- composed of orbital and palpebral parts
what are the eyelids called
superior tarsus
inferior tarsus
what attached the eyelids to either side
medial/lateral palpebral ligament
what lifts the eyelids
tendon of levator palpebrae superioris
what is the name of the corneoscleral junction
limbus
what does the lacrimal gland do and what innervates it
lacrimal fluid
CN VII
where does the lacrimal fluid go
Lacrimal gland >> over the eye >> lacrimal puncta >> Canaliculi >> lacrimal sac >> nasolacrimal duct >> inferior meatus
what is used to track the symmetry of bilateral eye positions/movements
corneal reflections
what are the 3 layers of the eyes
Fibrous (outer layer)
Uvea (vascular layer)
Retina (photosensitive)
what are the 2 parts of the fibrous outer layer
sclera - muscle attachment
cornea - 2/3 of refractive power
what are the 3 parts of the uvea middle layer
iris - pupil diameter
ciliary body - controls iris, shape of lens and secretion of aqueous humour
choroid - nutrition and gas exchange
what are the segments of the eye
anterior segment - in front of lens posterior segment - behind the lens - 2/3rds of eye
what is the anterior segment composed of
anterior chamber
- between cornea and iris
- contains aqueous humour
posterior chamber
- between iris and suspensory ligaments
- contains aqueous humour
what is the posterior segments composed of
contains vitreous body
- vitreous humour
- vitreous body common location for ‘floaters’
what is the route of circulation of aqueous
1 - Ciliary body secrete Aqueous
2 - Aqueous circulates within posterior chamber
2 - Aqueous passes through pupil into anterior chamber
4 - Aqueous reabsorbed into scleral venous sinus at iridocorneal angle
what is the role of aqueous fluid
nourishes lens and cornea
why is the iridocorneal angle clinically important
angle in “open-angle” & “closed-angle” glaucoma
what is included in the retina
optic disc
macula
fovea
where is the greatest density of cones
macula
what is the centre of the macula called and what is its features
fovea
area of most acute vision
where is the blind spot
at optic disc
what are the layers of the retina from anterior to posterior
1 - the axons of the ganglion cells
2 - the ganglion cells
3 - the photoreceptors
what lies anteriorly to the retina
the retinal veins and arteries
blood supply of the eye
internal carotid artery»_space;> carotid canal»_space;> cavernous sinus»_space;> ophthalmic artery
venous drainage of the eye
superior ophthalmic vein
what are the muscles of the eye
superior rectus inferior rectus medial rectus lateral rectus superior oblique inferior oblique levator palpebrae superioris
what is the innervation of the eye muscles
LR 6
SO 4
AO 3
what are the only eye muscles that do not have secondary movements
medial and lateral rectus
movement of Lateral rectus
ONLY abduct the eyeball
what muscles does moving lateral rectus move into plane
Superior Rectus
Inferior Rectus
(SILly)
what movement does SR have
when in abduction, SR can only elevate
what movements does IR have
when in abduction, IR can only depress
what movement does MR have
can only adduct eyeball. Bring towards nasal cavity
what muscles does MR bring into plane
Superior oblique
Inferior oblique
(MOO)
what movement does IO have
when in adduction, IO can only elevate
what movements does SO have
when in adduction, SO can only depress
what is a traumatic cause of diplopia
fractured zygoma
- suspensory ligaments attach here
- eye may be lowered towards orbital floor
- diplopia/double vision
what is a complication of a zygoma fracture
infraorbital NVB within the infraorbital canal can be damaged resulting in a general sensory deficit of the facial skin
what area does CN V1 supply the general sensory
- the upper eyelid
- the cornea
- all the conjunctiva
- the skin of the root/bridge/tip of the nose
what area does CN V2 supply the general sensory
- the skin of the lower eyelid
- the skin over the maxilla
- the skin of the ala of the nose
- the skin/mucosa of the upper lip
what area does CN V3 supply the general sensory
the skin over the mandible and temporomandibular joint
what provides the general supply of the angle of the mandible
C2, 3 spinal nerves
what is the afferent limb of the blink reflex
action potentials are conducted centrally via CN V1 to the trigeminal ganglion then in CN V (the trigeminal nerve) to the pons
what is the efferent limb of the blink reflex
action potentials are conducted peripherally in CN VII to the eyelid part of orbicularis oculi
how do sympathetic axons course from the CNS to the organs
cell body of presynaptic neurone in the CNS
»> presynaptic axon
ganglion of the cervical part of the sympathetic trunk
» postsynaptic axon
Organs
what happens at the synapse in sympathetic innervation
the presynaptic axon releases acetylcholine
what happens at the organ in sympathetic innervation
the postsynaptic axon releases noradrenaline to stimulate the organ to respond
where do presynaptic sympathetic axons synapse
in the superior cervical sympathetic ganglion
at what levels do sympathetic axons descend the spinal cord
T1 - L2
for innervation of the eye, what happens after the synapse at the superior cervical sympathetic ganglion
enter the internal carotid nerve & external carotid nerve
pass onto the surface of the internal and external carotid arteries
(internal is the one important for the eye)
what are the nerves with parasympathetic axons
CN III, VII, IX and X
where is the ganglion located in parasympathetic innervation
within the organ
what is released in parasympathetic innervation
presynaptic axon - ACh
postsynaptic axon - ACh
what does CN X supply
organs of the neck/chest & abdomen as far as the midgut
what nerve is responsible for parasympathetic innervation of the eye
CN III
what does CN III supply
SR, LPS - superior branch
MR, IR, IO, - inferior branch
presynaptic parasympathetic axons to the ciliary ganglion - inferior branch
what does CN III travel through
superior orbital fissure
what do ciliary nerves supply and control
autonomic axons to control the diameter of the iris (& pupil) & the refractive shape of the lens
what are the autonomic reflexes of the eye
- maximal eyelid elevation
- pupillary dilation/constriction i.e. the (pupillary) light reflex
- focussing the lens i.e. the accommodation reflex
- lacrimation
- the vestibulo-ocular reflex
- the oculocardiac reflex
what is the vestibulo-ocular reflex
turns the eyes in the opposite direction to a head movement (to stabilise the gaze on an object during head movements)
- CNS connections between CN VIII & CNs III, IV & VI
what is the oculocardiac reflex
- reflex bradycardia in response to tension on the extraocular muscles or pressure on the eye
- CNS connections between CN V1 & CN X
what are the sympathetic functions of the eye
open eyes wider
get more light into eyes
focus on far objects
emotional lacrimation
what are the parasympathetic functions of the eye
allow orbicularis oculi to work
get less light into eyes (protect retina from bright light)
focus on near object
reflex lacrimation (wash away stimulant)
how are eye opened wider
postsynaptic sympathetic fibres reach levator palpebrae superioris via:
the superior cervical sympathetic ganglion»_space;» the internal carotid nerve»_space;»the internal carotid plexus»»>axons carried on the ophthalmic artery and on its branches to the orbital structures
what is in control of dilating pupils
sympathetic innervation
dilator pupillae fibres
what is in control of pupil constriction
parasympathetic innervation
sphincter pupillae fibres
what is a fixed dilated/blown pupil a sign on
serious CN III pathology
what is the (pupillary) light reflex
shine light in one eye, both pupils constrict
eye stimulated = direct light reflex
eye not stimulated = consensual light reflex
how does the afferent limb differ from the efferent limb in the light reflex
afferent - ipsilateral CN II (the optic nerve) i.e. just side light is getting shone in
efferent - bilateral via CNs III (the oculomotor nerves)
how do ciliary muscles work to control the refractive shape of the lens
relaxes in “far vision” (no parasympathetics) the ligament tightens & the lens flattens to focus on distance
contracts in “near vision” (parasympathetic) the ligament relaxes & the lens becomes spherical to focus on reading
what are the 3 types of lacrimation
basal tears - clean, nourish and hydrate avascular cornea
reflex tears - extra tears in response to stimuli
emotional tears
what controls reflex tears
the afferent limb of the reflex is CN V1 (the ophthalmic nerve) from the cornea/conjunctiva
the efferent limb is parasympathetic axons originating from CN VII (the facial nerve)
what is raised intracranial pressure and what can cause it
Increase in pressure within the cranial cavity
Brain tumour, Head injury, Hydrocephalus (increased fluid around the brain), Meningitis, Stroke
what is the Monro-Kellie hypothesis
the pressure-volume relationship between ICP, volume of CSF, blood, and brain tissue, and cerebral perfusion pressure (CPP)
what are the components of intracranial pressure
brain
blood
CSF
what will people with RIP have
transient blurred vision double vision loss of vision papilloedema (swelling of optic disc due to increased ICP) pupillary changes
what are the optic nerves covered by
meninges
what is meninges and what are its layers
Protective coverings of brain and spinal cord
1 - dura mater
2 - arachnoid mater
3 - pia
what is in the subarachnoid space and where is it found
Circulating CSF and blood vessels
completely surrounds both brain & spinal cord - cushions and protects
between arachnoid mater and pia mater
features of dura mater
tough
sensory supply CN V
encloses dural venous sinuses
features of pia mater
Adheres to brain (and vessels and nerves entering or leaving)
where is CSF produced
choroid plexus of the lateral and third ventricles
where is CSF reabsorbed
dural venous sinuses
- via arachnoid granulations found in the arachnoid mater
where can the a sample of CSF be obtained
Lumbar puncture at L3/4 or L4/5
how many ventricles are in the brain and what are they called
4
right lateral, left lateral, 3rd and 4th ventricle
what connects the third and fourth ventricle
cerebral aqueduct
what is the circulation of CSF
1 - secreted by choroid plexus 2 - to right and left lateral ventricles 3 - then to 3rd ventricle 4 - via cerebral aqueduct 5 - the 4th ventricle 6 - into subarachnoid space 7 - reabsorbed from the subarachnoid space via the arachnoid granulations 8 - into the dural venous sinuses
what will happen to CNII with raised ICP
Raised ICP will be transmitted along the subarachnoid space in the optic nerve sheath and compress optic nerve
what will also happen as a result of raised ICP
Compress central artery and vein of the retina
Can lead to bulging or swollen optic discs
visual symptoms of raised ICP
transient visual obscurations (graying-out of vision), transient flickering blurring of vision constriction of the visual field decreased colour perception
what are signs of CN III damage
lose/slowness of pupillary light reflex, dilated pupil, ptosis, eye turned inferolaterally
what nerve of the eye is most susceptible to damage and why
CN IV
Long intracranial course
Susceptible to stretching and compression
signs of CN IV damage
Paralysis of superior oblique muscle
Inferior oblique is unopposed
- eye cannot move inferomedially
- diplopia when looking down
signs of CN VI damage
Paralysis of lateral rectus muscle
Eye cannot move laterally in horizontal plane
what are the two component of seeing via the retina
Rods
- sensitive to low levels of light
- night vision / peripheral vision
Cones
- detailed vision (acuity)
- colour vision
what are the parts of the visual pathway
Optic nerve
Optic chiasm
Optic radiation
Visual cortex
what are the common refractive errors
Emmetropia - no refractive error
Hypermetropia - long sighted
Myopia - short sighted
Astigmatism - defect in the eye or in a lens caused by a deviation from spherical curvature
Presbyopia - comes to us all. long-sightedness caused by loss of elasticity of the lens of the eye
