Vision 2 - The visual pathway Flashcards
what is the visual field?
everything you see with one eye
how can you test someones visual field?
confrontation test
automated perimetry
is your visual field up right or upside down on your retina?
your visual field is formed upside down and inverted on your retina
describe the visual pathway.
light rays enter each eye
travel through the optic nerve
both nasal fibres cross at the optic chasm
the optic tract now contains fibres from temporal half of the ipsilateral eye and the nasal fibres from the contralateral eye
the optic tract then synapses at the LGB
from here optic radiation passes behind internal capsule to reach the primary visual cortex
where is the primary visual cortex found?
the occipital lobe
where is the LGB found?
its part of the thalamus
where is the optic chasm found?
directly onto of the pituitary gland
what is the clinical significance of the optic chasm being found onto of the pituitary gland?
if someone has a pituitary tumour, one of the first symptoms is visual disturbances
is someones optic nerve got damaged on the right side what would this cause?
blindness in the right eye
if the optic chasm got damaged what would this result in?
bilateral hemianopia
if the optic tract got damaged on the right side what would this result in?
contralateral homonymous hemianopia
if the optic radiation is damaged what would this result in?
contralateral homonymous hemianopia
what side of the visual field does the right visual cortex see?
the left side (from both eyes)
what is the name for the condition in which there is misalignment of the eyes?
strabismus (squint)
what are the different types of strabismus?
esotropia - convergent quint
exotropia = divergent squint
how do you test for strabismus?
shine a light in their eyes
the light spot should be equal in both eyes
what are the functional consequences of strabismus?
amblyopia (lazy eye)
diplopia (double vision)
how does amblyopia occur as a consequence of strabismus and how is it corrected?
the brain suppresses the image of on eye which leads to poor vision without any pathology
corrected by wearing eye patch in early childhood to stimulate the lazy eye
how does diplopia occur as a consequence of strabismus?
usually occurs as a result of nerve palsies which cause the strabismus
describe the pathway way of fibres which activate the pupillary reflex.
fibres which activate the reflex don’t go to the LGB
they leave the optic tract and enter the midbrain
they stimulate the occulomotor nerve nucleus
part of the nucleus is EWN which has parasympathetic fibres
these parasympathetic fibres pass into the orbit and synapse of ciliary ganglion
post synaptic fibres then go through short ciliary nerves to the constrictor pupillae to constrict it on both side = pupillary reflex
in the pupillary reflex, what nerve does the fibres stimulate?
occulomotor nerves nucleus
what type of fibres does the pupillary reflex stimulate?
parasympathetic
what is the term for pupils that are different sizes and what condition does this occur in?
Aniscoria
Horners syndrome
what are the common causes for absent or abnormal pupillary reflex?
diseases of the retina - detachment , degeneration or dystrophies
diseases of optic nerve - optic neuritis (frequently seen in MS)
diseases of the CN III (efferent limb)
CN III palsy can occur in which medical condition?
diabetes
in CN III palsy due to diabetes, the pupillary reflex is normal, why?
the parasympathetic fibres aren’t damaged so the reflex is normal
in someone with CN III palsy due to diabetes, if they didn’t have a pupillary reflex, what would you suspect?
cerebral artery aneurysm = emergency
horners syndrome causes what eye abnormality?
aniscoria (pupils different sizes)
why does aniscoria occur in corners syndrome?
due to damage of the sympathetic innervation of the pupil
what are the main features of Horners syndrome?
aniscoria = pupils different sizes
mitosis (excessive constriction of the affected eye)
ptosis (drooping of the eyelid)
anhidrosis (loss of sweating on the affected side)
why could a pan coast tumour of the lung cause horners syndrome?
horners syndrome can occur due to disruption of the sympathetic fibres at any point in the thoracolumbar outflow
