L13 - Neuro-opthalmological disorders Flashcards
1. Revise visual pathways up to and behind the optic chiasm 2. Describe types of visual field loss and how these correspond to certain locations within the visual system. 3. Learn the chief causes of visual field loss. 4. Describe the common disorders of the extraocular muscle system (squint / straibismus, double vision and amblyopia) 5. Learn the common / important causes of double vision (nerve palsies, myasthenia gravis. thyroid eye disease, mitochondiral disease / CPEO)
What would a lesion in the left optic nerve result in?
Blindness in left eye.
Information from temporal and nasal fields cannot be brought down.
Blindness in left eye is known as….
Left Anopia
A lesion along the optic chiasm would result in?
Nerves that cross over and capture images on temporal visual fields cannot send this info.
- Blindness in temporal visual field from both right and left eye.
- Bitemporal Haemianopia
Blindness in temporal visual field in both eyes is known as….
Bitemporal Haemianopia
- commonly caused by chiasmal lesions.
What would occur if there was a lesion on the left side just after the optic chiasm?
Loss of vision on the left nasal field and right temporal field.
What is Hemianopsia?
Visual field loss on the left or right side of the vertical midline.
Why does homonymous hemianopsia occur?
- Right half of brain has visual pathways for the left hemifield of both eyes.
- Left half of brain has visual pathways for right hemifield of both eyes.
Describe optic disc?
Where optic nerve and vessels of eyeball pass through.
What is the macula?
contains fovea.
Fovea
- area containing many pigmented cells (cone cells)
- pigmented cells of retina allow for high resolution
Damage of the macula may lead to?
Loss of central vision.
What occurs during macula degeneration?
aka central schomata
- loss of central vision because of damaged macula.
What is known as constricted visual fields?
When only macula of eye remains.
Patient has tunnel vision
- observed in glaucoma
What nerve also brings information to midbrain?
optic nerve
Monocular visual loss may occur due to?
lesion affecting on eye or optic nerve anterior to optic chiasm.
How is pupil response in disease of the eye?
Usually normal.
However in optic nerve disease the pupil response is impaired.
Describe Amaurosis Fugax?
- Causes sudden, reversible loss in vision lasting up to 30 mins.
- Complete and rapid recovery.
- Usually due to embolism from ipsilateral carotid artery to retinal artery.
What is a transient ischaemic attack?
Caused by temporal disruption in blood supply to part of brain ‘mini stroke’.
What are the symptoms of a transient ischaemic attack?
Face - dropped on 1 side? person may not be able to smile
Arms - weakness, numbness in arms, unable to lift
Speech - slurred, garbled?
Time - call 999!
What is optic neuritis?
Inflammation of optic nerve.
Causes visual loss that commonly evolves over 3-10 days then gradually improves over days to weeks.
What are some symptoms of optic neuritis?
Pain behind eye.
Flashing lights on eye movement.
Describe the visual pathway?
- Photoreceptor’s convert light energy into neuronal signal, passed onto biopolar cells.
- Bipolar cell to Amacrine cell to Ganglion cell
- ganglion cell axons exit retina via optic nerve.
- nasal fibers from each eye cross over at optic chiasm and terminate in opposite sides of brain.
- optic tract carries fibers from chaism to LGN.
- fibers leave LGN as optic radiations that terminate in visual cortex of occiptal lobe.
Inattention to the contralateral visual field without a field defect occurs when…
Lesions of parietal lobe, esp. on RHS.
Patients tend to ignore stimuli presented to the left visual field.
e.g. If asked to draw clock, patients typically miss numbers of squish numbers into right half.
What is Agnosia?
Inability to recognise or categorise objects presented visually in the presence of normal acuity.
- objects might be identified if palpated
What is anterior ischaemic optic neuropathy?
- Sudden loss of vision
- due to an interruption of blood flow
- to the anterior part of optic nerve
- aka optic nerve head.
Optic neuritis is found typically in adults between the ages of ?
20 - 50 y/o
Optic Ishaemia usually affects patients aged…
> 50s
What is giant cell arteritis? GCA
- Causes inflammation of medium and large sized arteries.
- Potentially fatal.
- Can damage entire optic nerve head
- leading to permanent massive vision loss.
What is nonarteritic AION caused by? (5)
- Drop in BP to such a degree that BS to optic nerve decreased.
- Increased pressure inside eyeball
- Narrowed arteries
- Increased blood viscosity
- Decreased BF to optic nerve where it leaves back of eye.
What is the main symptom of NA-AOIN?
Sudden, painless loss of blurring of vision in one eye.
Pneuonmic:
Remembering optic chiasm
TRUNC T- Temporal R- Retina U- Uncrossed N- Nasal C- crossed
Describe a disadvantage of the location of the optic chiasm?
- Located just above pituitary.
- Can be compressed by pituitary tumours.
- This leads to bitemporal field loss.
Describe the structure of the Lateral genuiculate nucleus?
6 cellular layers with thin sheets of myelinated fibers sandwiches between them.
where might you find a lesion in inferior quadrantanopia?
Parietal lobe.
e. g. legion in left parietal lobe will cause right homonymous lower quandrantopia.
- loss of lower nasal quadrant from the left eye and the lower temporal quadrant from the right eye.
Describe superior quadrantopia?
loss of same upper quadrant from each visual field.
- temporal damage.
e. g. lesion in left temporal lobe will cause a right homonymous upper quadrantanopia. - loss of upper nasal quadrant from left eye and upper temporal quadrant from right eye.
Lesion in left parietal lobe may result in?
- loss of lower nasal quadrant from the left eye
- the lower temporal quadrant from the right eye.
Lesion in in left temporal lobe will result in?
- loss of upper nasal quadrant from left eye
- loss of upper temporal quadrant from right eye.
State some causes of visual field loss?
Glaucoma Vascular disease Tumour Retinal disease Optic Neuritis Hereditary diseases Inflammatory processes
Generalised constriction of the visual field could be due to… (4)
Glaucoma
Retinitis Pigmentosa
Hysteria
Chronic high intracranial pressure
Glaucoma
Condition that causes damage to eye’s optic nerve, gets worse over time.
- tends to be inherited, may not show up till later life.
- often linked to buildup of pressure inside eye.
Retinitis pigmentosa
- Genetic.
- Involves breakdown and loss of light sensitive cells in retina
- hence causing difficulty seeing at night and loss of peripheral vision.
What are the two general types of photoreceptor?
- Rods
- in outer regions of retina, allow u to see in dim and dark light - Cones
- mostly in central portion of retina, allow us to perceive fine visual detail and colour..
Anisometropia
Both eyes have unequal refractive power.
- each eye can be either nearsighted (myopia), farsighted (hyperopia) or a combination of both (antimetropia)
A difference in power of how many diopters is used to label a condition anisometropia?
Difference in power of 2 DIOPRTERS usually an accepted threshold to label the condition anisometropia.
What is amblyopia?
Even when correcting the refractive error of a patients eye, the patients eye is still not correctable to 20 /20.
What broadman area is the primary visual area?
Broadman area 17.
What is nystagmus?
Uncontrolled movement of the eyes.
Movements are usually side to side but can also be up and down or in a circular motion.
Strabismus
Crossed eyes.
Visual condition in which a person can not align both eyes simultaneously under normal conditions.
Describe how a occulomotor nerve palsy may occur?
CN III
Compression of nerve.
Inadequate blood flow to nerve.
How may compression of the occulomotor nerve occur?
Posterior communicating artery aneurysm.
Disorder causing herniation of brain. (Herniation occurs when brain is forced downward through a small opening in sheets of tissue that separates brain into compartments)
Occulomotor palsy may …
Impair eye movements, the response of pupils to light, or both.
A palsy of the Trochlear nerve may affect?
CN IV
Can affect Vertical eye movements.
What is special about the trochlear nerve?
Longest and thinnest nerve, hence trauma susceptibility.
Patients suffering from trochlear palsy may…
- Double vision, however tilting head to side opposite the affected eye can elimate them.
Describe thyroid eye disease?
e. g. Graves ophthalmopathy
- potentially sight-threatening ocular disease, generally occurs in patients with hyperthyroidism.
What are some common clinical signs of thyroid eye disease?
- Retraction of eyelid
- Exophthalmos
- Restriction of eye movements.Q
What is CPEO?
- Chornic progressive external ophthalmoplegia
Type of eye disorder characterized by slowly progressive inability to move eyes and eyebrows.
What age ranges does CPEO usually manifest in?
Typically manifests in young adult years.
Most common manifestation of mitochondrial myopathy.
Describe mitochondrial disease?
Group of disorders caused by dysfunctional mitochondria.
- can be caused by mutations in the mitochondrial DNA.
Patients with CPEO typically present with?
Ptosis - drooping eyelids
Difficulty to move eye.
