Neuro-Ophthalmology Flashcards
Revise autonomic control of pupil size
Pathway causing Miosis
Revise pupil reflex pathway
Pathway causing Mydriasis
Describe the Visual Pathway
Starts in the retina and projects into the occipital cortex. Lesions after the retina typically result in hemianopia and quadrantanopia. Lesions of the retina tend to result in scotomas
Describe the defects which can be produced by lesions along the visual pathway
List the 4 divisions of the optic nerve (CN2)
Divisions:
- Intraocular: shortest and ends at the lamina cribrosa
- Intra-orbital: longest and ends at optic foramen
- Intracanalicular: through the optic canal into the middle cranial fossa
- Intracranial: ends at the chiasm
Axons of the retinal ganglion cells wrap together to form what?
The optic nerve
Blood supply to the optic nerve
Intraocular → short posterior ciliary artery
Rest → ophthalmic artery (Pial vessels)
Where do axons travelling from the nasal part of the retina leave the optic nerve and decussate?
At the optic chiasm
Anatomical location of the optic chiasm
The chiasm sits anterior to the hypothalamus and superior to the pituitary gland
Describe the following defects of the chiasm
- Willebrand’s knee
- Middle Chiasmal Lesions
- Posterior Chiasmal Lesions
Note:
Remember that the lower part of the retina is responsible for the upper part of the visual field, and the upper part of the retina sees the lower visual field
Optic Tract
There are 2 optic tracts, one for each hemisphere
- They project from the chiasm to the LGN
- They carry ipsilateral temporal axons and contralateral nasal axons
Defects produced by lesions of the optic tract
Lesions of the tract result in contralateral incongruous (asymmetrical) homonymous hemianopia.
I.e lesion of the right tract will result in left homonymous hemianopia
Lesions of the tract can also produce contralateral afferent RAPD because over half the fibres have already crossed at the chiasm
What are Optic Radiations
Projections from the LGN to the visual cortex. The radiations are divided into superior (Dorsal loop) and inferior (Meyer’s loop) projections
Compare the two loops of the optic radiations
In what area of the brain does cognitive visual perception occur?
The occipital cortex
List 2 lesions in the occipital cortex
What visual field defects would be produced?
Systemic hypoperfusion or back of head injury → homonymous hemianopia with central scotoma
Posterior cerebral artery occlusion → homonymous hemianopia with macular sparing (central vision spared)
What are Visual Streams
How far do the visual fields extend
- 50° superiorly
- 60° nasally
- 70° inferiorly
- 90° temporally
Revise scotomas
Revise the different types of field defect terminology
- Scotoma: Area of visual loss surrounded by normal visual area
- Absolute scotoma: No light seen at all
- Relative scotoma: Brighter lights are seen
- Homonymous: Same visual field quadrants are affected in both eyes
- Hemianopia: 2 quadrants of vision loss
- Quadrantanopia: 1 quadrant vision loss
- Congruousness: the degree to which the defects are the same in both eyes, increases as you move posteriorly in the tract
- Seidel scotoma: enlargement of blind spot
A Goldmann Perimeter. The clinician sits on the opposite side and moves the stimulus at the edges of the bowl.
What does the report from the Humphrey visual field test of the right eye show?
It shows a complete loss of the temporal visual field.
What is used to measure visual fields
Perimetry
Compare the 3 types of perimetry
A Humphrey visual field analyser. The patient looks into the bowl and static stimuli a presented at various locations of the field, the patient responds when they see a stimulus. This data is plotted automatically
Goldmann visual field record sheet
What conditions are associated with Red-Green loss
Optic nerve problems such as neuritis
(NOT glaucoma!)
What conditions are associated with Blue-Yellow loss
Macular problems such as AMD
And glaucoma!
List the extraocular muscles of the eye
List the 4 important rules/laws which apply to the Extraocular muscles of the eye
Origins of the extraocular muscles
- All recti originate from the common tendinous ring (Annulus of Zinn).
- SO originates from the lesser wing of sphenoid
- IO originates from the orbital floor
Which extraocular muscle of the eye inserts closest and furthurest to the limbus
- Medial rectus inserts closest to the limbus
- Superior rectus inserts furthest away
Innervation to the extraocular muscles of the eye
- CN6 → LR
- CN3 → All other recti + IO
- CN4 → SO
Actions of the extraocular muscles
- Elevation → SR (Primary) + IO
- Depression → IR (Primary) + SO
- Adduction → MR (Primary) + SR + IR
- Abduction → LR (Primary) + SO + IO
- Intorsion → SO
- Extorsion → IO
Where are the nucleus locations of the CN3,4, 6
- CN3 → dorsal midbrain at the level of the superior colliculus
- CN4 → dorsal midbrain at the level of the inferior colliculus
- CN6 → ventral to 4th ventricle at pontine tegmentum near the paramedian pontine reticular formation
CN3 Pathway
CN4 pathway
CN6 pathway
When is CN4 most likley to be damaged
CN4 is most likely to be damaged by trauma because it has the longest course.
When is CN6 most likley to be damaged?
CN6 is most likely to be damaged by raised ICP because it travels within Dorello’s canal where it is tightly packed against hard bony structures.
Revise cavernos sinus anatomy
CN3 actions
- Ipsilateral IO IR MR
- Contralateral SR
- Bilateral levator
- Ipsilateral sphincter pupillae
CN4 actions
Contralateral SO
CN6 actions
Ipsilateral LR
What controls ‘gaze’
Your gaze is controlled at 3 levels:
- supranuclear (initiates movement at the cortex)
- Intra-nuclear (coordinates movement at the brainstem)
- Infra-nuclear (efferent nerves to muscles)
List the 3 types of gaze
- saccades
- smooth pursuit
- vestibular ocular movements
Saccades
The horizontal gaze pathway can be tricky to grasp at first but is well worth learning because it is frequently tested.
Smooth pursuit
Slow tracking of moving objects
- Initiated by the Parietal-occipital-temporal (POT) region, ipsilateral to the tracking direction
- For example, right slow pursuit is initiated by the right POT
Vestibular ocular movements
Keep eyes stable with head movement
- Initiated at brainstem level, does not involve the cortex
Tested by dolls head reflex
- The eyes move when the head is moved to keep them looking in the same direction
- If the dolls head reflex is intact, then the internuclear pathways must be intact
What is Nystagmus
Nystagmus is repeated, involuntary oscillation of the eyes. It can be physiological or pathological
What is physiological nystagmus
Occurs at extremes of gaze or by following fast-moving objects
Causes of pathological nystagmus
- Upbeat → medullary lesions
- Downbeat → Arnold-Chiari malformation
- Vestibular → vestibular lesion causes nystagmus towards the lesion
- Latent → horizontal nystagmus that starts when one eye is covered. Beats towards the covered eye. Associated with infantile esotropia
- Convergence retraction nystagmus → bilateral convergence and retraction of the globe on attempted upgaze
Congential nystagmus may be caused by what?
Congenital nystagmus can be caused by bilateral cataracts and neurological disorders
What is Optic neuritis
Inflammation of the optic nerve, anywhere from the chiasm to the optic disc.
The most common cause is demyelination.
Classification of optic neuritis
- Papillitis: Inflammation of the optic disc. Typically presents in post-viral children with flame haemorrhages and an oedematous optic nerve
- Retrobulbar neuritis: disc is spared but the segment behind the eyeball is affected. The disc looks normal in this acute setting. More common in adults
- Neuroretinitis: The disc and retina are both involved. Occurs in Lyme disease and cat scratch
Disc Structure
- High myopes have larger discs and hyperopes have smaller discs
- Axons travel within the neuroretinal rim of the disc, not at the centre. The centre of the disc is vascular and contains the central retinal vessels
- Macular fibres are responsible for central vision and count for over 1/3 of the axons of the disc, this is why optic neuropathies commonly cause central/paracentral scotomas
What causes cat scatch disease
Bartonella Henselae, transmitted by cats
Compare typical vs atypical optic neuritis
Compare the clinical manifestations of optic nerve disease vs macular disease
Papilloedema
Papilloedema is swelling of the optic disc directly from raised intracranial pressure. Disc oedema is the generic term for a swollen optic disc.
What effect does acute papilloedema have on vision
Causes an enlarged blind spot
What effect does acute papilloedema have on vision
Causes an enlarged blind spot
What effect does chronic papilloedema have on vision
Results initially in the loss of the inferior nasal quadrant of vision
Fundus image of a patient with papilledema. There are multiple haemorrhages and the disc margin is blurred.
How can Anterior Ischemic Optic Neuropathy (AION) be classified?
Compare these
Arteritic or Non-arteritic
Pathology of MS
T-cell mediated type 4 autoimmune neurodegenerative disorder of myelin in the central nervous system, which leads to inflammation and sclerosis.
Classification of MS
- Relapsing remittent - Episodes of MS which come and go
- Primary progressive - The episode lasts >1 year and gets worse continually with time
- Secondary progressive - Like relapsing remittent but the baseline condition is worse after each episode
Presentation of MS
Classically presents in women in their 20s with optic neuritis.
Investigations for MS
Diagnosis is based on episodes of neurological dysfunction in the history alongside CNS lesions, disseminated across time and space respectively.
List/ Discuss 3 Other Optic Nerve Disorders
Describe the following 3 pupil abnormalities
- Marcus-Gunn Pupil
- Argyll-Robertson Pupil
- Adie’s Pupil
What is Holmes-adie syndrome?
Aldie pupil + decreased lower limb reflexes
What is Horner Syndrome
Horner syndrome is a triad of: ptosis, anhidrosis and miosis.
It is caused by a lesion in the sympathetic pathway to the head and neck.
Lesions of first, second and third order neurons in Horners
- First order : lesions of brain and spinal cord
- Second order : Pancoast tumour and neck trauma
- Third order: no anhidrosis. Caused by cavernous sinus lesions and internal carotid dissection
Why is there no anhydrosis in third order Horner syndrome
Because the secretomotor fibres that supply the sweat glands of the face leave this pathway before the third-order neuron.
Therefore, a lesion of the third neuron will not affect sweat gland function.
How can the lesion in Horners be localised
Administration of various topical medications bilaterally helps localise which order neuron is likely to be affected, and then relevant imaging of the high yield sites are conducted for diagnostics.
Horners Syndrome - Topical Cocaine
- Used to confirm horner syndrome, a lesion somewhere along the sympathetic chain
- It blocks noradrenaline reuptake → enhances sympathetic effect and causes mydriasis in normal people
- In Horner syndrome, the sympathetic pathway is broken so the Horner pupil will not dilate to Cocaine, but the normal one will
Horners Syndrome - Topical Apraclonidine
- Used to confirm Horners
- Apraclonidine is an alpha agonist that causes mydriasis in normal people
- In Horner syndrome, the sympathetic pathway is broken and the effector muscles at the end of the pathway are hypersensitive. When Apraclonidine is administered, the Horner eye dilates even more than the normal eye.
- The principle underlying this test is denervation hypersensitivity
- Remember that medications are applied bilaterally, to both eyes.
Horners Syndrome - Topical Hydroxyamphetamine
- Used to distinguish 3rd order lesions from the others (postganglionic or preganglionic). The ganglion in question is the superior cervical ganglion; it sits at the carotid bifurcation
- Hydroxyamphetamine releases noradrenaline from the 3rd order neuron endings (postganglionic) to the dilator pupillae muscle which causes pupil dilation. If there is a 3rd order lesion, the pupil will not dilate. If there is no lesion, or a lesion of 1/2 order, the pupil will dilate
Horners Syndrome - Topical Dilute Adrenaline
- Used to distinguish 3rd order lesion from the others (postganglionic or preganglionic). The ganglion in question is the superior cervical ganglion; it sits at the carotid bifurcation
- Adrenaline activates postsynaptic effector terminals to bring about the sympathetic response - pupil dilation. In Horner syndrome there is denervation hypersensitivity in these receptors, especially in 3rd order disease. If there is a 3rd order lesion, significant dilation is seen. Preganglionic Horner syndrome does not dilate as much.
What 2 topical medications can be used to diagnose Horners
Cocaine and Apraclonidine
What 2 topical medications can be used to localise 3rd order disease in Horners
Hydroxyamphetamine and dilute adrenaline
Painful Horner syndrome is what until proven otherwise?
Carotid dissection until proven otherwise!
Urgent carotid angiogram is needed
How are CN3 lesions characterised
Medical or surgical
Medical lesions characteristically spare the pupil (i.e pupil reflexes are intact and there is no anisometropia).
How do medical vs surgical CN3 lesions differ
Medical
- Much more common than surgical type
- Typically caused by microvascular complications of diabetes and hypertension
- The pupil will react to light
Surgical
- Characteristic surgical causes include posterior communicating artery aneurysm and uncal hernia
- The pupil will not react to light
Why is the pupil only affected in surgical causes of CN3
The pupil is affected in surgical causes because they violently compress the pupillomotor fibres which run within CN3.
Microvascular problems are unlikely to affect these superficial fibres because of the rich blood supply via pial vessels.
Hence the pupil reflexes are spared in medical CN3 lesions.
Presentation of CN3 lesion
- Ptosis
- Ophthalmoplegia with only abduction preserved
- Down and out eye
- Dilated pupil (in surgical type)
Investigation for CN3 lesion
- Urgent CT angiography in acute surgical third nerve palsies to rule out posterior communicating artery aneurysm
- Medical cases should still get neuroimaging and workup for vascular risk factors, but this is far less serious in comparison.
What is Weber’s stroke syndrome
CN3 palsy + contralateral hemiparesis
CN4 Lesion causes
CN4 lesions are typically either congenital, traumatic or microvascular (most common)
Presentation of CN4 lesion
Patients present with vertical diplopia and hypertropia (superior displacement of the eye)
What special test is used to identiy CN4 lesion
Parks Test / Park-Bielschowsky 3 step test
- Find the hypertropic eye in the primary position
- Evaluate how the diplopia changes with horizontal gaze direction
- Image separation is worse in contralateral gaze direction
- I.e if the left eye is affected, diplopia is worse on right gaze
- Evaluate how diplopia changes with head tilt
- Image separation is worse on ipsilateral head tilt
- I.e if the left eye is affected, diplopia is worse on left head tilt.
Most common cause of CN6 lesion
The most common cause is microvascular disease resulting in nerve ischemia.
Presentation of CN6 lesion
- Presents with horizontal diplopia and esotropia (the affected eye is deviated inwards).
- Abduction is severely limited
What is Gradenigo Syndrome
- A classic syndrome of otitis + CN6 palsy
- CN6 travels very close to the auditory structures so an infection in the ear can result in CN6 palsy.
- Characteristically caused by pathology at the petrous apex of the temporal bone
What is Internuclear Ophthalmoplegia (INO)
Internuclear refers to communication between CN6 (Pons) nucleus and the contralateral CN3 (midbrain) nucleus. This communication is by the medial longitudinal fasciculus (MLF). A lesion of the MLF results in internuclear ophthalmoplegia.
Normal MLF Function
- Normally, the MLF coordinates the CN6 and CN3 to permit horizontal gaze
- The 2 muscles needed for horizontal gaze are CN6 (innervates LR) and CN3 (innervates MR)
- The MLF connects the CN6 nucleus to the contralateral CN3 nucleus
- E.G the RIGHT MLF connects the LEFT CN6 nucleus to the RIGHT CN3.
Identifying The Lesion INO
Bilateral INO (WEBINO/EBINO)
Bilateral internuclear ophthalmoplegia (INO) occurs when both MLF are diseased. It is also called WEBINO or EBINO. ‘WE’ stands for wall-eyed in WEBNIO. ‘E’ stands for Exotropic in ‘EBINO’. WEBINO is an outdated term as it conveys a negative image.
Findings of Bilateral INO
In the primary position, both eyes are slightly deviated outwards, hence wall-eyed/exotropic.
On attempted LEFT gaze
* abducting nystagmus of the LEFT eye
* unable to adduct the RIGHT eye
On attempted RIGHT gaze
* abducting nystagmus of the RIGHT eye
* unable to adduct LEFT eye
One and Half Syndrome
The ‘one’ refers to horizontal gaze palsy. This is caused by a lesion of the CN6 nucleus/PPRF. For example, a RIGHT CN6 nucleus lesion will stop the function of the right CN6 and the LEFT MLF. This means that neither eye will move on attempted RIGHT gaze. But LEFT gaze would be completely normal.
The ‘half’ refers to INO.
Findings of One and Half Syndrome
The Pontine paramedian reticular formation (PPRF) and the CN6 nucleus are separate entities but are very closely associated, and can be considered as one entity for image below.
List 2 other Gaze abnormalities
Myasthenia Gravis
Myasthenia gravis is an autoimmune disorder of the neuromuscular junction. It is relevant in ophthalmology because it affects the eyelid/eye muscles.
Pathology of Myasthenia Gravis
Anti-acetylcholine antibodies target the postsynaptic acetylcholine receptors at the neuromuscular junction, causing fatigability.
- Repetitive movements worsen fatigue and weakness.
- Because the eyelid muscles are used extensively throughout the day, ptosis and diplopia towards the end of the day is a classic sign.
Lambert-Eaton syndrome
Another disease of the neuromuscular junction, but it affects the presynaptic calcium channels. Fatigue improves with muscle use.
Presentation of Myasthenia Gravis
- Ptosis which is worse at the end of the day
- Diplopia is worse after extended reading or TV watching
- Respiratory depression (Myasthenic crisis)
Investigations for Myasthenia Gravis
- Autoantibodies: Anti-AChR and Anti-MUSK
- Repetitive nerve stimulation shows decrease in action potential amplitude
Why is a CT thorax indicated in Myasthenia Gravis
A CT thorax is indicated in these patients because a thymoma can cause myasthenia gravis.
In these cases, thymectomy can cure the disease
Management of Myasthenia Gravis
Acetylcholinesterase inhibitors such as pyridostigmine are used in long term management
Steroids are used in myasthenic crisis
Myotonic Dystrophy
An autosomal dominant disorder is characterised by the failure of muscle relaxation after contraction.
Pathology of Myotonic Dystrophy
Caused by trinucleotide expansion of CTG on the DMPK gene (chromosome 19)
Presentation of Myotonic Dystrophy
- Presents by the 2nd decade of life
- Bilateral ptosis, cataracts(Christmas tree) and ophthalmoplegia.
- Muscle weakness with delayed relaxation (myotonic grip)
- Frontal baldness, testicular atrophy and cardiomyopathies
Investigation for Myotonic Dystrophy
Diagnosis made by DNA testing
Kearns-Sayre Syndrome
A rare cause of chronic progressive external ophthalmoplegia of mitochondrial inheritance. This is ultra-rare and has only been included for completeness, and to demonstrate that general myopathies often affect the extraocular muscles
Presentation of Kearns-Sayre Syndrome
- Can present at birth, most cases manifest well before the 2nd decade of life
- Bilateral ptosis and ophthalmoplegia
- Pigmentary salt and pepper retinopathy
- Cardiac conduction defects
Compare Neurofibromatosis (1&2) vs Tuberous Sclerosis
Inheritance of Neurofibromatosis and Tuberous Sclerosis
Autosomal Dominant
Types of Strabismus
There are 2 broad types of strabismus (tropias and phorias):
- A tropia is when the eyes are always deviated (manifest deviation)
- A phoria is a more subtle deviation which is hidden by binocular fusion, and becomes apparent when this is broken during testing.
What is Strabismus
Strabismus is caused by abnormalities in extraocular muscle function. It can be treated with prism lenses or surgery, depending on the extent of the deviation.
Types of Tropias and Phorias
Further classified according to the direction of eyeball deviation
- Exotropia - outwardly turned (Divergent squint)
- Esotropia - inwardly turned (Convergent squint)
- Hypertropia - upwardly turned
- Hypotropia - downwardly turned
The same terminology applied to phorias
Most common form of childhood strabismus
Esotropia
Esotropia is associated with what?
Hypermetropia
How can Esotropia be classified
Compare these
Accommodative
- Fully accommodative → Esotropia resolves with correction of hypermetropia
- Partially accommodative → Esotropia partially resolves with cycloplegic hypermetropic correction and also needs treatment for amblyopia
- Convergence excess → Esotropia for only nearly vision caused by high convergence. Manage with bifocal glasses or squint surgery
Non-accommodative
- Infantile Esotropia is the commonest non-accommodative type
Exotropia is typically associated with what
Myopia
How can Exotropia be classified
Compare these
Intermittent vs Constant
Intermittent
* More common
* Exotropia which worsens based on distance or near gaze.
* Near exotropia is relatively common in in the adolescent population
Constant exotropia
* Presents in infants as a result of gross abnormalities in ocular motility
What is responsible for stereopsis?
Binocular vision is also responsible for stereopsis (depth perception).
You need inputs from both eyes to perceive depth.
Special Tests for Strabismus
- Titmus, TNO, Lang, synoptophore → Stereopsis
- worth 4-dot, Bagolini glasses and synoptophore → Sensory fusion
- Prism cover test → Motor fusion (alignment)
Hirschberg Test
Allows the clinician to identify tropias
- A light from an ophthalmoscope is shone, and the corneal light reflex is located.
- In orthophoria, the cornea light reflex should be right over the centre of the pupil.
- In tropias, the corneal light reflex is deviated.
I.e In a right exotropia:
The corneal light reflex of the right eye will be more medial to the pupil. Demonstrating outward deviation of the eyeball.
Cover Test
What are Restriction Syndromes
Extraocular muscle action can be mechanically restricted for various reasons. This can lead to strabismus.
List 2 types of Restriction Syndromes
- Duane Syndrome
- Brown Syndrome
Duane Syndrome
Thought to be caused by aberrant co-innervation of both the LR and MR by CN3
- This makes the globe retract during adduction.
- Systematically associated with Goldenhar syndrome
- There are 3 types based on additional features:
1: esotropia + abduction deficit
2 : exotropia + adduction deficit
3: esotropia + abduction and adduction deficits
Duane type 1 is the commonest
Brown Syndrome
Limited elevation when adducted
- Upgaze causes a characteristic clicking sensation
- Caused by mechanical restriction of the superior oblique
- Can be found congenitally or after trauma
Strabismus Surgery techniques and outcome
Amblyopia
The visual pathways develop in childhood by the age of 8. Any visual problems during this age can lead to abnormal visual development, which is then permanent throughout life. This is why strabismus and amblyopia are so important in paediatrics.
Pathology of Amblyopia
- Anything that affects vision in childhood can potentially lead to amblyopia
- Common causes include strabismus and refractive error
- Other causes include ptosis and congenital cataract
Management of Amblyopia
- Occlusion therapy - the good eye is occluded with an eye patch to allow the amblyopic eye to develop properly and catch up
- Atropine penalisation - atropine is topically administered to the good eye, thereby reducing its visual acuity, and allowing the amblyopic eye to develop properly
