Neuroopthalmology Flashcards
What is CNII made up of?
convergence of retinal ganglion cells
which axons of CNII correspond to which visual fields?
temporal axons to nasal field
nasal axons to temporal fields
What are the 4 parts of CNII?
- Intraocular, shortest 1mm: exits posteriorly via lamina criborsa (scleral opening)
- intraorbital (longest, 25mm), myelinated covering and ends at optic foramen
- Intracanalicular: where the optic nerve exits the orbit through the optic canal to enter middle cranial fossa
- Intracranial fossa: ends at optic chiasm
What is the blood supply for CNII?
intraocular: short posterior ciliary artery
intraorbital to intracranial: pial vessels of ophthalmic artery
Where is the optic chiasm located?
anterior to the hypothalamus and usually directly superior to pit gland
Where do axons representing the temporal retina within the chiasm continue?
ipsilateral
Where do axons representing the nasal retina continue within the chiasm?
decussate at the chiasm and to the contralteral optic chiasm
Desrcibe the path of inferonasal axons
turn anteriorly within the chiasm to join the contralateral CNII (Willebrand’s knee) before continuing back to optic tract
How is the body’s circadian rhythym controlled?
a few photosensitive retinal ganglion cells axons connect with the suprachiasmatic nucleus of the hypothalamus
How do optic tracts connect to the optic chiasm?
with the lateral genticulate nuclei
Which retinas does the optic tract convey signals from?
contralateral nasal retina
ipisilateral temporal retina
What is the function of optic radiations?
connects lateral genitculate nuclei to the occipital lobe
What do superior optic radiations represent?
inferior visual field quadrants
Describe the path of superior optic radiations
pass through parietal lobe - terminate in the primary visual cortex
this is superior to a calacrine sulcus in the cuneus gyrus)
Describe the path of inferior optic radiations (meyer’s loop)
represent superior visual field
temporal lobe - primary visual cortex, inferior to the calacrine sulcus (in the lingual gyrus)
Where is the macula represented?
posteriorly, lateral to the tip of the calcarine sulcus
Where is the oculomotor nerve nucleus located?
dorsal midbrain at the level of the superior colliculus
What are the motor functions of the oculomotor nerve?
Ipsilateral innveration to IO, IR and MR
Contralateral innervation to SR
Bilateral innervation to levator muscle
Describe the pathway of the oculomotor nerve
exits brainstem through interpeduncular fossa, passing between posterior cerebral artery and superior cerebellar artery
travels close to uncus of temporal lobe, vulnerable to uncal hernations
next, lateral wall of cavernous sinus superior to CNIV and bifurcates into superior and inferior branch at anterior aspect of sinus
Where does the oculomotor nerve enter the orbit?
Enters orbit thorugh the SOF within the annulus of Zinn.
What does the superior branch of the oculomotor nerve innervate?
superior rectus and levator muscle
What does the inferior branch of the oculomotor nerve innervate?
Medial Rectus, Inferior rectus and inferior oblique
What fibres is CNIII accompanied by?
parasympathetic, originating from the Edinger-westphal nuclei
located in the midbrain dorsal to oculomotor nuclei,
innervates sphincter papillae and ciliary body muscles
What nerves are included in the pupillary light reflex?
CNII afferent limb
interconnecting neurons in the midbrain
CNIII efferent limb
Describe the pathway of the pupillary light reflex
originate from retinal ganglion cells
fibres exit the optic tract before reaching the LGN and entering midbrain to synapse on the ipsilateral pretectal nucleus
pretectal nuclei projects bilateral fibres to the contralateral and ipsilateral edinger westphal nuclei
preganglionic parasympathetic fibres from edinger westphal travel along with CNIII and exit the inferior branch of CNIII to synapse on the ciliary ganglion
from ciliary ganglion, postganglionic sympathetic fibres are carried via short ciliary nerves to innervate the ciliary body muscle and sphincter pupillae
What is the accommodation reflex?
adaption of the eye when focusing on a near object
How does the accommodation reflex work?
Increasing lens curvature: ciliary body muscles contract via parasympathetic from edinger Westphal, leading to relaxation of lens zonules
Pupil constriction: activation of the sphincter pupillary via parasympathetic from Edinger-Westphal
Eye convergence: contraction of media recti via CNIII
Where are the trochlear nerve nuclei located?
in the midbrain, at the level of the inferior colliculus
Which muscles to the trochlear nuclei innervate?
contralateral SO
Describe the pathway of the trochlear nerve
passes through the lateral wall of the cavernous sinus inferior to CNIII and enters the SOF above the common tendinous ring
Describe the CNIV characteristics
only cranial nerve that exits dorsally from the brainstem
fewest number of axons of all nerves
longest unprotected intracranial course
Where is the abducens nucleus located?
In the pontine tegmentum ventral to the fourth ventricle
nucleus is located near the paramedian pontine reticular formation and surrounded by looping fibres of CNVII
Where does the abducens nerve (CNVI) exit the brainstem? Describe the pathway
pontomedullary junction and crosses over the petrous apex of the temporal bone through an osteofibrous channel (dorello’s canal)
then travels through the cavernous sinus, lateral to the internal carotid
then enters the orbit via the SOF, through the tendinous ring to innervate the LR muscle
Where is CNVI most susceptible to stretching
at Dorello’s canal
Which system is responsible for pupillary dilatation and contraction of the Muller muscle?
Sympathetic
Describe the pathway for pupilry dilation
First order neurons: start at the posterolateral hypothalamus and synapse at the intermediolateral cell column between C8 to T2 (cilispinal centre of Budge)
Second order preganglionic neurons: leave centre of budge, travel over the lung apex and synapse at the superior cervical ganglion at the carotid bifurcation.
- this is where the sudomotor fibres exit to course with the external carotid and supply the sweat glands of the face
3rd order post ganglionic neurons: travel around the internal carotid artery to finally innervate the dilator pupillae via the long ciliary nerves (branches of the nasociliary nerve)
How are supranuclear eye movements controlled?
voluntary / reflex control
Voluntayr movements are initiated in the frontal eye field, brodmann area 8 in the frontal lobe
reflex movements coordinated via occipital cortex and superior colliculus in response to a visual stimulus
What are the 3 types of supranuclear motor movements?
saccadic eye movements
smooth pursuit movements
vestibulo-ocular movements
Describe saccadic movements
fast eye movements which involve the rapid fixation of a desired object onto the fovea
abrupt change of point fixation when switching from one object to the next
Describe the angular speed and duration of saccadic movements
600 degrees / s
lasting around 30-100 milliseconds after a latency of approx 200 milliseconds
What are voluntary saccadic movements initiated by?
frontal eye field
Describe how activation of FEF leads to saccadic movements
Right FEF = looking left
Describe the pathway of the projections from the frontal eye field
go directly or via the superior colliculus to the contralateral PPRF (which lies ventral to the abducens nucleus in the brainstem)
How does PPRF activation lead to saccadic movements?
activates the ipsilateral abducens nucleus and sends impulses through the medial longitudinal fasciculus to activate the contralateral oculomotor nucleus
How are vertical saccades controlled?
rostral interstitial nucleus of the MLF
What is smooth pursuit?
slow movements of the eye designed to keep a moving stimulus fixed at the fovea
describe the latency of smooth pursuit
100 milliseconds
Where are smooth movements initiated from?
parieto-occipital areas
What are vestibulo-ocular movements?
Stabilise the eye relative to head movements
Describe how vestibulo-ocular movements work
when head is moving and eyes are fixed
sensory information of the SEMICIRCULAR CANALS results in the movements of the eyes in the opposite direction to the head movement
how do vestibulo-ocular movements occur?
occurs via projections from the vestibular nuclei to creanial nerves and PRF
What is optic neuropathy?
damage of the optic nerve
What are the common signs of optic nerve dysfunction?
dVA
Dyschromatopsia
Visual field Defects: centrla scotomas, arcuate /
altitudinal defects
diminished contrast sensitivity
absolute / relative afferent pupillary defect
What are the cuases of optic neuritis?
Retrobulbar neuritis
Papillitis
Neuroretinitis
Describe retrobulbar neuritis?
optic nerve behind the globe is affected
optic nerve head is not involved, giving rise to a normal looking optic disc on fundoscopy
more common in aduls
Describe papillitis
Hyperaemia and oedematous optic disc with associated peripapillary flame shaped haemorrhage
optic nerve head is affected
more common in children especially post viral
Describe neuroretinitis
Papillitis with involvement of the retina
occurs in cat scratch disease and lyme disease
What is multiple sclerosis?
AI condition characterised by demyelination of the CNS
female predominance presenting in 3rd/4th decades of life
more common in countries further from equator
Describe the systemic features of MS
parasthesia
muscle cramping and wakness
bladder, bowel and sexual dysfunction
cerebellar dysfunction: tremor, dysarthria, ataxia (charcot’s triad)
Lhermitte sign: electrical shock on neck flexion
Uhthoff phenomenon: worse symptoms in warm temperature
Describe the ophthalmic features of MS
retrobulbar optic neuritis: acute unset of unilateral retrobulbar pain exacerbated by eye movements, dVA, central scotoma, dyschromatopsia and RAPD
-followed by spontaneous resolution after a few months
Internuclear opthalmoplegia
nystagmus
What investigations are used for MS
MRI - demyelinating plaques disseminated in space and time
Lumbar Puncture: oligoclonal bands in CSF
Describe how MS is managed
IV methylprednisolone for 3 days
oral prednisolone for 11 days
What is neuromyelitis optica?
A demyelinating disorder characterised by severe retrobulbar optic neuritis and transverse myelitis in three of more vertebral columns causing:
muscle weakness
increased tone
spasms
What key feature is found in neuromyelitis optica?
IgG antibodies against astrocytic aquaporin-4
What is neuroretinitis?
Inflammation of the optic nerve with oedema spreading from the optic nerve head along the papillomacular bundle to reach the macula
formation of exudates around macula gives a ‘macular star’ appearance
mainly caused by cat-scratch disease
What is cat scratch disease?
caused by: bartonella henslae (gram negative rod)
via cat scratch / bite
features:
- fever lymphadenopathy
- neuroretinitis: unilateral, painless dVA, papilitis, mild optic nerve dysfunction and star pattern of macular exudates
- uveitis
- granulomatous conjunctivitis
What is anterior ischaemic optic neuropathy?
occurs due to damage to the optic nerve as a result of ischaemia
can cause optic neuropathy in the elderly due to occlusion of short posterior ciliary artery
split into arteritic and non-arteritic
What is Leber hereditary optic neuropathy?
MITOCHONDRIAL inherited disease caused by ganglion cell degeneration
mitochondrial DNA mutation occurs at the 11,778 (most common and worst prognosis)
Describe the aetiology of non-arteriotic AION
HTN, diabetes,
sleep apnoea
physiologically small or absent cup (structural crowding of the optic nerve head)
Describe the vision loss of non-arteriotic AION
sudden
painless
unilateral
VA usually >6/60
often inferior / superior visual field defect
Describe the disc findings in non-arteriotic AION
usually segmental hyperaemic disc swelling with peripapillary splinter hemorrhages
What are the investigations used in non-arteriotic AION?
BP, blood sugar, examination of optic disc and exclude GCA
FA: delayed optic disc filling
What is the tratments for non-arteriotic AION?
treat underlying cause
What is the aetiology of arteriotic AION?
GCA most commonly
Describe the vision loss in arteriotic AION
sudden
painful
unilateral with high risk to fellow eye if untreated
severe visual loss <6/60
Describe the disc findings of arteriotic AION
chalky white diffuse swollen disc
Describe the associated symptoms of arteriotic AION
scalp tenderness, headache and jaw claudication
What investigations are used for arteritic AION?
ESR
CRP
temporal artery biopsy (high specificty but low sensitivity)
FA: delayed choroidal and optic disc filling
how is arteritic AION treated?
High dose IV methylprednisolone and oral prednisolone
What are the features of Leber Hereditary optic neuropathy
Unilateral initially with bilateral ocular involvement over weeks to months
painless visual loss
central / centrocaecal scotomas
Triad of: pseudo-oedema, peripapillary telangiectasia and tortuosity of medium-sized retinal arterioles
optic atrophy in late disease
What investigations are used for leber’s optic neuropathy?
Family history and genetic testing
OCT which can show optic nerve oedema (early) or atrophy (late)
What is nutritional optic neuropathy?
aka tobacco-alcohol ambylopia
caused by vit B, copper and folic acid deficiencies
medications (ethambutol, amiodarone or sildenafil) and other toxic causes
what are the features of nutritional optic neuropathy?
gradual, progressive, painless bilateral dVA and centrocaecal scotomas
Dyschromatopsia
What is papilloedema?
bilateral disc swelling secondary to raised ICP
what are some causes of raised ICP?
tumours,
haemorrhages
hydrocephalus
idiopathic intracranial HTN (typically in young obese females)
What are the features of an increased ICP?
headache worse in the morning
nausea and vomiting
pulsatile tinnitus
unilateral or bilateral transient visual loss with a duration of seconds
enlarged blind spot
diplopia due to CNVI palsy
HTN, bradycardia and bradypnea (Cushing reflex)
What signs are seen on teh optic disc in papillodema?
Hyperaemia and blurred margins of the optic disc (early)
swelling and elevation of the whole optic disc with peripapillary hemorrhages (late)
What are tilted discs?
bilateral, small optic discs tilted inferonasally
associated with high myopia
superotemporal field defect are common
What is morning glory anomaly?
unilateral and causes severe dVA
Characterised by FUNNEL-SHAPED EXCAVATION of the optic disc and surrounding retinal tissue
characteristically, the retinal vessels emerge from the periphery of the optic nerve head rather than from the centre
associated with retinal detachment
What is an optic disc pit?
characterised by a greyish oval depression in the optic nerve head, usually located temporally
complications: exudative retinal detachment
What is an optic disc coloboma?
occurs due to defect in embryonic fissure closing
cane be sporadic or associated with Golden har syndrome, micropthalmos and CHARGE syndrome
glistening white bowl shaped excavation of the disc (inferior part predominantly affected) causing superior field defect and dVA
What are optic dis cdrusen?
Collection of mucoproteins and mucopolysaccharides that progressively calcify in the optic disc, present as yellow or white bodies on the optic disc
commonly bilateral
varying degrees of blurring and visual loss
associations: retinitis pigmentosa and angiod streaks
What is optic nerve hypoplasia?
caused due to underdevelopment of the optic nerve
patients often present with visual loss and a double ring sign
risk factors include genetic diseases and maternal use of recreational drugs, smoking and alcohol
