L15: The visual system Flashcards
the path an image takes from the eye is
- optic nerve
- past the optic chiasm into the
- optic tract,
- to the lateral geniculate nucleus
- to the primary visual cortex in the back of the brain
what is the thalamic relay centre in the brain for images
geniculate nuclei
where in the brain does everything from the left visual field of both eyes go
right hemisphere
where do the fibres become purely one visual field
after the optic chiasm in the optic tract
if there is a lesion in the optic nerve on the right side what happens
loss information from the right eye only
homonymous defect =
when the information in a single visual field in both eyes is affected
what is damaged in a homonymous defect
optic tract
what can you get if only a part of optic radiation is damaged
quadrantanopia
what is macular sparing
very centre of visual field is the only preserved vision
why does macular sparing happen
central eye is highly innervated and has a good blood supply so less likely to be damaged
what happens when the optic chiasm is damaged
heterogeneous hemianopia
what is heterogeneous hemianopia
loss of vision in opposite hemifields in each eye
2 parts of outermost layer of eye
- cornea
- sclera
sclera=
white of eye
cornea=
clear bit at the front
3 continous layers of the vascular layer
- iris
- ciliary body
- choroid
choroid=
network of blood vessels
neural layer of the eye=
retina
2 humours of eye
aqueous humour
vitreous humour
aqueous humour 2 parts =
anterior chamber
posterior chamber
where is the anterior chamber
just inside the cornea
where is the posterior chamber
between the lens and the iris
2 blood supplies in the eye
- the choroid
- retinal blood vessels
fovea=
region of highest resolution vision, highest density of neurons
what is the fovea good at
fine detail and high sensitivity
conjugate eye movement=
eyes move in the same direction
4 types of conjugate eye movement
- vestibulo-ocular
- optokinetic -saccade
- smooth pursuit
1 type of disconjugate eye movement
-vergence
saccade=
directs eyes towards visual target
name 6 extraocular muscles
- Superior oblique
- inferior oblique
- superior rectus
- medial rectus
- lateral rectus
- inferior rectus
2 muscles on top of one another
- levator palpebrae superioris
- superior rectus
which muscle is on a kinda hook
superior oblique
which muscles elevate the eye
- superior rectus
- inferior oblique
which muscles depress the eye
- inferior rectus
- superior rectus
what adducts the eye
medial rectus
what abducts the eye
lateral rectus
what muscles move the top of the eye towards the nose
superior oblique
superior rectus
what muscles move the top of eye away from the nose
inferior rectus
inferior oblique
cranial nerve innervation of medial rectus, superior rectus and inferior oblique
oculomotor (3)
cranial nerve innervation of superior oblique
4- trochlear nerve
cranial nerve innervation of lateral rectus
6-abducens
final common pathway of all eye movements
brainstem nuclei
which is the most sensitive part of the body with the most nerve endings
cornea
what connects the lens to the ciliary body
zonules
what allows you to change pupil size
muscles in the iris
miosis=
pupil constriction
miosis nervous control=
parasympathetic
what is active in miosis
iris sphincter
mydriasis=
pupil dilation
what is active in mydriasis
iris dilator
what nervous controls mydriasis
sympathetic
what did david bowie have
Anisocoria - different levels of pupil dilation
accommodation=
the process of focusing an image with the lense
what looking at a distant object what shape is the lense
flat
looking at distant objects what position are the eyes in
diverge
in near objects what do the eyes do
converge
nervous control of the accommodation reflex-=
parasympathetic
3 factors of the pupil accommodation reflex
- pupil constriction
- lens accommodation
- convergence of the eye
what is the most important neural structure in controlling the accommodation reflex
Edinger-westphal nucleus (in brainstem)
what ganglion do neural impulses to the eye travel in
ciliary ganglion
most common cause of blindness
cataracts
cataracts=
opacification of the lens caused by compaction and protein deposition
name 5 risk factors for cataracts
ageing trauma diabetes smoking genetic
treatment for cataracts
lens removed under local anaesthetic and replaced with artificial lens
5 risk factors for glaucoma
- raised intraocular pressure
- high BP
- long corticosteroid use
- severe myopia
- eye injury
2 types of glaucoma
- primary open-angle glaucoma
- acute angle-closure glaucoma
cause of primary open-angle glaucoma
trabecular meshwork clogged
which glaucoma is acute onset
acute-angle-closure
cause of acute angle closure glaucoma
iris bows, closes anterior chamber angle and blocks drainage
symptom of primary open-angle glaucoma
gradual vision loss (peripheral to central)
symptoms of acute angle-closure glaucoma
sudden vision loss/ blurring; red eye; severe eye/ head pain; nausea/ vomiting
3 tests for glaucoma
- tonometry
- fundus photography
- visual perimetry
what does tonometry measure
intraocular pressure
what does fundus photography look at
optic nerve
visual perimetry=
measure visual fields
glaucoma treatment (5)
- beta blockers
- alpha2-adrenoceptor agonist
- carbonic anhydrase inhibitors
- prostaglandin analogues
- miotics (muscarinic agonists)
what produces aqueous humour
ciliary processes
where does the aqueous humour travel
passes from the posterior chamber behind the iris through the pupil and into the anterior chamber
what drains the aqueous humour
trabecular meshwork
anterior chamber angle=
the angle between the cornea and the iris
once the aqueous is through the trabecular meshwork where does it drain
schlemm’s canal
what blood supply supports the outer retina
choroid
what blood supply supports the inner retina
retinal vasculature
only part of the eye without retinal vasculature=
fovea
outermost layer of the retina=
photoreceptors (rods and cones)
middle layer of the retina =
- bipolar cells
- amacrine and horizontal cells
what do bipolar cells do
pass information from the receptors into the ganglion cells
what do amacrine and horizontal cells do
communication horizontally across the retina
what is spread away more in the fovea
the first 2 layers (ganglion and bipolar cells)
what photoreceptors are presents in the very centre of the retina
only cones
what are cones good at
high resolution vision
photoreceptors in the peripheral retina=
more rods
where are both rods and cones fatter
peripheral
scotopic photoreceptors=
rods
scotopic=
night time vision (very sensitive to light)
photopic=
cones
photopic=
daytime vision (less sensitive) -higher resolution
3 types of cones
red cones
green cones
blue cones
red/green colour blindness is passed down
recessively on X chromosome
what do protanopes lack
red cones
what do deuteranopes lack
green cones
what do tritanopes lack
blue cones (NOT X-linked)
2 layers of the lateral geniculate nucleus=
magnocellular
magnocellular=
large cells, light/dark greyscale, low resolution
4 layers of the lateral geniculate nucleus=
parvocellular
parvocellular=
small cells, higher resolution, colour
where is the primary visual cortex
back of the brain
where are the central visual fields processed in the brain
very back of the brain
where are the peripheral visual fields processed
more anteriorly in the visual cortex
where is the brain specialises in colour
ventral surface V4
where in the brain is sensitive to motion
V5 lateral brain
sense found in
parahippocampal place area
faces found in
fusiform face area
objects found in
lateral occipital cortex
