Visual System Flashcards
Duction
Duction – Eye Movement in One Eye
‘Simultaneous movement of both eyes in the same direction’
what is this called?
Version
_______ : Simultaneous movement of both eyes in the opposite direction
Vergence
Convergence
– Simultaneous adduction (inward) movement in both eyes when viewing a near object
Saccade
– short fast burst, up to 900°/sec Reflexive saccade to external stimuli Scanning saccade Predictive saccade to track objects Memory-guided saccade
Lacrimal system
types of tears
Basal
Reflex
emotional
Tears - where produced
where do they flow from?
gather?
exit?
Drain through two puncta openings on medial lid margin
flow through superior and inferior canaliculi
gather in tear sac
exit via tear duct into nasla cavity
What is a basal tear?
It produces tear at a constant level,
even in the absence of irritation or stimulation
Reflex tears
response to occular irritation , increased tear production
Emotional tear
crying
Tear reflex pathway
afferent pathway > CNS > Efferent pathway > lacrimal gland
afferent pathway : cornea, CNV1 [ophthalmic trigeminal ]
efferent pathway : parasympathetic innervates lacrimal gland
Neurotransmitter : acetylcholine
What is the ‘Tear Film’ -
Where is it found?
Use?
Thin layer of fluid : composed of 3 layers> lipid layer, aqueous> mucious layer
covers healthy cornea, maintaining smooth cornea to air surface
important for maintaining clear vision, removal of debris
Why is the layering of the tear film important?
lipid layer allows for reduced tear film evaporation
produced by meibomian glands
aqueous layer important in protection against harmful bacteria ; provides nutrients and oxygen to surrounding tissue
mucinous layer contains mucin
Thin, transparent tissue that covers the outer surface of the eye
Conjunctiva
3 layers forming coat of eye?
Sclera
Choroid: pigmented vascular
retina : ligh into neuro impulses transmitted to brain via optic nerve
sclera properties
high water content
the tough, opaque tissue that serves as the eye’s protective outer coat.
what happens if you hydrate the eye?
It becomes white
usually low water content
so can be a clear window to look through / look into eye
how does cornea get oxygen / glucose?
oxygen from air
glucose via fluid absorbed by endothelium
uvea
lies between sclera and retina
Iris, Ciliary Body, Choroid
How are cataracts formed?
Lens losing its transparency with ages resulting in an opaque lens known as Catarct
Most sensitive part of the retina?
fovea found within the macula
It has the highest concentration of cones, but a low concentration of rods
Retinal Structure
Photoreceptors [1st] > Bipolar Cells [2nd] > Retinal ganglion cells [3rd]
Rods vs Cones
Rods : Night vision , 100 times more sensitive to light : 120 mill
Cones: faster response , less sensitivity. fine vision, colour vision 6 million
Deuteranomaly
not completely colour blind but they don’t perceive the colour red.
full colour blindness
achromatopsia
what is responsible for capturing light rays?
retina
where is the macula located?
centrally in the retina,
where is the fovea found?
centre of macula
peripheral vision?
extensive loss of visual field
navigation vision loss
shape, movement night vision
central vision
detail day vision, colour
fovea has the highest concentration of cone photoreceptors
refraction
light goes from one medium to another velocity changes
light bends path changes
convex
takes light rays and brinsg them to a point
concave lens
diverging lens which takes light rays and spreads them outwards
example of a converging lens?
camera
convex lens
adequate correction between axial length and refractive power is known as what?
emmetropia
ametropia is ?
refractive error
axial length and refractive power mismatch
myopia
short sight blurred distance vision squinting headache treatment correction with a negative lens contact lens removal of lens to reduce refractive power of the eye by surgery
hyperopia
Long sighted
light rays converge BEHIND retina = blurred NEAR vision so reading
eye strain / hence headache
why?
short globe
not enough refractive power
hyperopia symptom
visual acuity at near tends to blur relatively early
short sight
children can get learning difficulty
treatment
glasses
lens
surgery
astigmatism
2 focal lines rather 1 focal point - 2 points
heredity
refractive media is not spherical
refract differently as refractive media is not spherical
= blurred vision, frontal headache
eye strain and pain
astigmatism
symptoms
asthenopic symptoms
blurred vision
distortion of vision
head tilting / turning
adaptation for near vision
pupillary miosis to increase depth of field
convergence to align both eyes towards a near object
accommodation to increase the refractive power of the lens for near vision
presbyopia
onset 40 onwards
naturally occuring loss of accommodation
corrected by reading glasses
treatment for presbyopia
bifocal glasses
trifocal glasses
progressive power glasses
presbyopia correction
spectacle lenses : monofocal lenses , cylindrical lenses, multifocal lenses
signal from Eye to Visual Cortex pathway
eye optic nerve optic chiasm optic tract lateral geniculate nucleus optic radiation - 4th order neuron primary visual cortex or striate cortex
visual pathway retina
first order neurones are ?
rod and cone retinal photoreceptors
second order neurons?
retinal bipolar cells
third order neurons
retinal ganglion cells
what are third order neurons?
optic nerve CN II
partial decussation at optic chiasm - 53%
optic tract
LGN relays visual info to visual cortex
where is the lateral geniculate nucleus
thalamus
if lesion is found anterior to optic chiasm?
then visual defect is in one eye primarily
i
crossed fibres originate
temporal visual field
uncrossed fibres
nasal visual field
what produces contralateral homonymous Hemianopia?
As a rule, visual pathway lesion posterior to the chiasma produces contralateral Homonymous Hemianopia in both eyes.
Bitemporal Hemianopia
causes?
Damage to the crossed nasal ganglion fibres,
results in deficit in temporal visual field loss in both eyes simultaneously
pituitary adenoma
causes of
Homonymous Hemianopia
stroke
Cerebrovascular accident
Homonymous Hemianopia
with Macular sparing
stroke causes primary visual cortex damage
leads to contralateral homonymous hemianopia
but macula is spared - as the area representing it receives dual blood supply from BOTH right and left posterior cerebral arteries
shine light
pupillary response?
which nerve?
pupil constriction
decrease spherical abberations&glare
mediated by CN III - PARAsympathetic nerve
dark
pupillary response?
dilatation increases
mediated by sympathetic nerve : iris radial muscle
afferent pathway
draw this out
rod & cone photoreceptors synapse on Bipolar cells > synapse on retinal ganglion cells
pupil- specific ganglion cells exits at posterior third of optic tract before entering lateral geniculate nucleus
afferent pathway synapses on Edinger-westphal nuclei
where is the edinger-westphal nucleus?
brainstem
efferent pathway
edinger-westhpal nucelus > occulomotor nerve efferent >
synapses at ciliary ganglion
short posterior ciliary nerve
pupillary sphincter
what is the efferent pathway mediated by?
parasympathetic nerve
afferent pathway in left eye senses bright light
what happens?
pupillary constriction in both eyes
as afferent pathway stimulates efferent pathway of both eyes
Pupillary Reflex afferent pathway
A small sub-section of retinal ganglion cells participate in the Pupillary Reflex Pathway.
They exit the Optic Tract before the Lateral Geniculate Ganglion,
and synapse upon the Dorsal Brain Stem,
as shown by the red and green pathways in the diagram
consensual light reflex?
why does this happen?
Consensual Light Reflex refers to the constriction of the pupil from the fellow eye.
neurological basis : afferent pathway stimulates both efferent pathway
efferent defect in left eye
response to light shone in left eye?
right eye constricts
left eye unresponsive
right eye constricts regardless of light shone in R/L eye
afferent right eye defect ?
pupillary response to light?
weak pupillary reflect in both eyes
how to demonstrate weakened response ?
stimulate one eye at a time
swinging torch test
when light is in undamaged eye both pupils are constricted
when light is swung to damaged eye, pupils actually dilate as there is relative to the other eye reduced drive for pupillary constriction
- damaged afferent pathway unable to process to brainstem that bright light is being shone as it is weak compared to to other eye
convergence happens when?
viewing a near object
simultaneous adduction, inward movement of both eyes
vergence happens when?
simultaneous movement of both eyes in the opposite direction
6 muscles of the eye?
4 straight muscles superior rectus medial rectus lateral rectus inferior rectus
superior oblique
inferior oblique
superior oblique
- attached high on temporal side passes under the superior rectus moves eye DOWN & OUT travels through tochlea
which muscle moves the eye DOWN and OUT?
superior oblique
which 3 cranial nerves are involved in eye movements?
CN III
CN IV
CN VI
what is eye movement in one eye called?
Duction
what is version?
simultaneous movement of BOTH eyes in Same direction
simultaneous movement of BOTH eyes in OPPOSITE direction
vergence
which muscle moves eye up?
superior rectus
attached at 12 o’clock
inferior rectus
eye movement?
moves eye down
where does the lateral rectus attach?
where does it move eye?
temporal side of the eye
at 3 o’clock
moves eye toward outside of head
eye movement
Up and OUT
inferior oblique
attached low on the nasal side of the eye
diagonal pattern of movement
when does Saccade occur?
scanning text when reading a book
which muscle doesnt come from a cone at the back of the orbit?
where does it come from
inferior oblique
comes in nasally
medal rectus
attaches nasal side
moves eye toward the middle
which muscle raises the eyelid?
what is it’s innervation
levator palpebrae superioris
3rd CN
which muscles are innervated by CN III
superior branch-
1) superior rectus,
2) levator palpebrae superioris
inferior branch
1) Inferior Rectus – depresses eye
2) Medial Rectus – adducts eye
3) Inferior Oblique – elevates eye
4) Parasympathetic Nerve – constricts pupil
depression of eye ?
CN 3
inferior branch
inferior rectus muscle
superior oblique
innervation
CN IV
tochlear
depresses eye
Abducens
6th CN
lateral rectus
lateral
abducts eye
what causes adduction?
medial rectus innervated by inferior branch of CN III
Oculomotor nerve
when does the oculomotor divide?
when it enters the orbit
divides into superior and inferior
lateral rectus muscle testing ?
lateral Rectus muscle action is best tested in the abducted position
medial rectus muscle action
Medial Rectus muscle action is best tested in the adducted position.
Superior Rectus muscle action
Superior Rectus muscle action is best tested in the elevated and abducted position.
Inferior Rectus muscle action
Inferior Rectus muscle action is best tested in the depressed and abducted position.
.
Inferior Oblique is best tested
Inferior Oblique is best tested in the elevated and adducted position
Superior Oblique is best tested
Superior Oblique is best tested in the depressed and adducted position.
Supraduction
Supraduction – one eye
Supraversion
Supraversion – both eyes
Dextroversion
eye movement to right
Levoversion
left eye movement
3rd nerve palsy
down and out eye droopy eyelid( levator palpebrae superioris)
why does the eye droop down and out in 3rd nerve palsy
Unopposed superior oblique innervated by fourth nerve (down)
Unopposed lateral rectus action innervated by sixth nerve (out)
6th nerve palsy
inability to abduct
deviated inwards
double vision worsen on gazing to the side of the affected eye
