2 - neurological eye problems Flashcards
what nerves are the eye muscles innervated by?
LR6 SO4 AO3
= lateral rectus - CN VI
= superior oblique - CN IV
= medial rectus, inferior rectus, superior rectus, inferior oblique, sphincter pupillae & levator palpebrae superioris (LPS) - CN III
what is presentation of CN VI palsy?
= lateral rectus not working so can’t look laterally & also since lateral rectus like holds eye out a bit, when palsy eye naturally squints in medially
what is main cause i should know for CN VI palsy?
raised intracranial pressure (it’s not very common but most critical since kills quick)
- also tumours, vascular, congenital bla bla
what is main cause of CN IV palsy i should know about?
- congenital is main cause of CN IV palsy
what is presentation of IVth palsy?
IV = superior oblique palsy so when abduct can’t look down
= people have vertical squint and often adopt compensatory head posture to reduce double vision (like look tilting to side)
what is presentation of CN III palsy?
CN III = supplies all eye muscles but lateral rectus & superior oblique so eye = looks down & out (also w large pupil & slightly closed eyelid)
what is main cause of CN III palsy i should know?
aneurysm
describe the visual pathway?
- photoreceptors (cones & rods) stimulated and make electrical impulse
- electrical signals passed to ganglions forming optic nerve (CN II) and goes to middle cranial fossa in optic canal
- R&L optic nerves cross over at optic chiasm (nasal swap but temporal stay same side)
- optic tracts run to thalamus where nerves synapse at lateral geniculate nucleus
- optic radiations then carry from lateral geniculate nucleus to occipital lobe
what type of blindness seen in optic nerve lesions?
ipsilateral monocular blindness = one eye fully blind (since no cross over or anything yet)
what type of blindness seen at optic chiasm?
bitemporal hemianopia = loss of temporal vision in both eyes (since nasal fibres are crossing)
what type of blindness seen in optic tract problem?
affects temporal of one eye and nasal of other eye - so lose vision of like left hand side of each eyeball
what type of blindness in optic radiations problem?
contralateral quadrantanopia = pie in the sky/pie on the floor - where loss of quarter on same side of eyeball e.g. top left of left eyeball (temporal) & top left of right eyeball (nasal)
what blindness seen in occipital lobe problem?
homonymous hemianopia with sparing of macula - half blindness on same side of each eyeball
what are causes of optic nerve blindness?
- ischaemic optic neuropathy (giant cell)
- optic neuritis = like MS, progressive
- tumours
what are causes of optic chiasm blindness?
pituitary tumours (common)
- also craniopharyngioma & meningioma
what are optic tract & radiations causes of blindness?
- strokes (common)
- tumours
- demyelination
