visual pathway 2 Flashcards
what is the optic nerve
collection of axons of ganglion cells
exit back of eye through hole in sclera
optic disc (nerve) can be seen at the back
what is the neuroretinal rim
where all the nerve fibers are
tends to be pink
cup in centre (nothing there)
if cup is bigger rim gets thinner
what should you comment on when looking at the optic nerve
margin
colour
cup
what are 4 important optic nerves to know
healthy
swollen-edge of nerve not as distinct (increased pressure)
cup bigger (glaucoma)
diffusely pale optic nerve (nutrioninal def)
if pupils are different size what does that mean (sensory or motor)
motor/ efferent issue (sympathetics and parasympathetics)
if the same size you will be looking for a sensory issue
-shine light
-involving retina and optic nerve
what is the technique for testing pupil
measure pupil diameter in light and dark
– less reactive is abnormal
test direct response
-shine light in one eye and response in same eye
test indirect response
-shine light in one eye and response in same eye
check for a relative afferent pupillary defect
check for accomodation
-alternating fixation on a distant from near target
how do you test motor system on observation
darken room
and difference accentuated
small is problem
-sympathetic issue
bright area
if difference in eye size increases
big pupil is problem
-parasympathetic issue
how do you test for RELATIVE AFFERENT PUPILLARY DEFECT
shine light on one eye for 2-3 seconds
rapidly move to fellow eye
normal- no change in size, brief constriction and returning to same state
if RAPD– PARADOXICALLY DILATE when light moves towards it
-common reason is GLAUCOMA
where do afferent axons join brainstem
lateral geniculate nucleus
1st synapse after leaving retina
nerves being divided up
6 layers
ipsilateral 2, 3, 5
contralateral 1, 4, 6
magnocellular (large axons, project to parietal lobes) 1 and 2
parvocellular (small axons, project to temporal lobes) 3,4,5,6
what is the line of gennari
myelinated fibres running from LGN to synapse in layer 4 of the striate cortex
what is the next synapse after LGN
into occipital lobe
line of gennari
what is the role of the occipital lobe
relay station
retinotopic map- direct physical relationship between spots on the retina and spots in the occipital lobe
bits of visual field project to specific parts occipital lobe
neural tuning is present-specific populations of cells will respond to:
-colour
-spatial frequency
-orientation
what is amblyopia
lazy eye
what is patching used for
critical period of visual development–as plasticity
patch good eye
eye is deprived of a clear image
commonly due to a uncorrected refractive error or a squint
improve input into the lazy eye
correct squint
glasses
patching
what vision would you get with age related macular degeneration
central scotoma
what vision would you get with diabetic eye disease
central scotoma
lipid deposition so retina stretched and thickened due to leaky blood vessels
blurry
what vision would you get with retinal detachment
typically top bit of retina comes off
causes:
develop awareness of poor vision in lower part and opposite part
what can cause chiasmal lesion
pituitary tumour
-vision bad up to down
craniopharyngioma
-vision bad down to up
what are most common post chiasmal lesions
stroke
space occupying lesions- tumours and bleeds
mostly affects both eyes as info is crossed over
what is quadrantanopias
what is occipital lobe lesions
what are the techniques for testing visual fields
ask patient to say if they can see all of your face
present open palms in temporal quadrants
how to create conscious vision
the process of vision
survey overall scene
locate and attend to one object amongst many
recognise this object
decide on an appropriate plan of motor action
all happening in parallel simultaneously.
two functional streams of visual info that complement each other
-what and where streams
discuss vision
eyeball
connections
brain
eyeball- optical front end and retina at the back
connections- optic nerve, chiasm and optic tract
brain-occipital, temporal, parietal, frontal lobes
