The Visual System Flashcards
what is required for control of eye movement?
visual stimuli
sensory info from eye muscles
head movement (direction, velocity)
auditory info (via sup colliculus)
limbic system (fear, excitement)
voluntary control (intention, plan)
what are the fxns of the visual system?
control eye movement
visual ID of objects
perception of the relationships bw objects and self
contribute to motor control
what muscles control the thickness of the lens?
ciliary muscles
when the lens is contracted is it thicker or thinner and does this allow for near or far vision?
when the lens is contracted, it’s thicker and allows for near vision
what is the optic disk?
blind spot
where all the ganglionic neurons are bundled and leave the eye
what is the fovea?
the area of the retina w/the most rods and cones for best visual acuity
describe the image of the retina?
inverted and flipped
where is the 4th quadrant (lower R) of the visual field in the retinal image
upper L
where is the 3rd quadrant (lower L) of the visual field in the retinal image?
upper R
where is the 2nd quadrant (upper R) of the visual field in the retinal image?
lower L
where is the 1st quadrant (upper L) of the visual field in the retinal image?
lower R
what is the 1st order neuron of the visual input from the retina to the cortex?
optic nerve
what is the path of the 1st order neuron for visual input?
optic chiasm–>optic tract–> lateral geniculate nucleus of the thalamus
what is the path of the second order for visual input
LGN–>optic radiation (geniculocalcarine tract)–>primary visual cortex (V1)
what is V1 responsible for?
conscious vision
what is another name for the V1 cortex?
calcarine cortex
what structures make up the midbrain?
tectum, pretectum, and superior colliculus
what is the visual fxn of the midbrain?
pupillary reflexes and orienting the eyes and head
what are the 2 streams that come from the V2 cortex?
dorsal action stream
ventral perception stream
what is the V2 cortex responsible for?
color and motion
what is the dorsal stream
the action stream
visual guidance for movement
what is the ventral stream?
the perception stream
visual ID of the object
where does the dorsal action stream flow?
to the posterior parietal cortex
where does the ventral perception stream flow?
to the occipitotemporal region
does the nasal or temporal retina cross the midline in the optic chiasm?
the nasal retina
does the nasal or temporal retina remain ipsilateral
the temporal retina
t/f: info from one visual field projects to the opposite visual cortex
true
where does light from the R visual field go to?
the nasal retina on the R
the temporal retina on the L
all axons leaving the chiasm in the L optic tract carry info from the __ visual field–> __ LGN–>__ V1 cortex
R, L, L
all axons leaving the chiasm in the R optic tract carry info from the __ visual field–>__ LGN–>__ V1 cortex
L, R, R
are visual pathway lesion named by the side you can or can’t see out of?
the side you CAN’T see out of
what is the visual loss with a R optic nerve lesion?
R monocular vision loss
what is bitemporal (heteronomous) hemianopsia?
loss of the medial retinal images and lateral visual field
if there is a loss of the medial retinal image, what is the loss in the visual field?
lateral
if there is a loss of the lateral retinal image, what is the loss in the visual field?
medial
what visual loss with an optic tract lesion?
homonymous hemianopsia
what is homonymous hemianopsia?
loss of the same side in both eyes
what is quadrantopsia?
loss of a quadrant of the vision that can be superior or inferior
what is the Edinger-Westphal nucleus?
the nucleus of CN 3 parasympathetic neurons (efferent of oculomotor reflexes) in the midbrain tegmentum
what are the oculomotor reflexes?
pupillary light reflex
accomodation reflex
what muscles are innervated by the neurons from the Edinger Wesphal nucleus?
pupillary sphincter and ciliary muscles
what is the pupillary light reflex?
light is shone in one eye and the pupils constricts in both eyes
what is the afferent of the pupillary light reflex? efferent?
afferent=CN 2
efferent=CN 3
what happens in ipsilateral direct pupillary light reflex when a light is shone in the L eye?
the L pretectal area receives the info and activates the L CN 3 parasympathetic nucleus
what happens in the indirect consensual pupillary light reflex when a light is shone in the L eye?
the L pretectal area receive the info and activates the R CN parasympathetic nucleus
info goes bilaterally
if there is a lesion to the R optic nerve, and a light is shined in the R eye, what is the direct response? consensual response?
no direct or consensual response
if there is a lesion to the L optic nerve, and a light is shined in the R eye what is the direct response? consensual response?
normal direct and consensual response
if there is a R oculomotor nerve lesion and a light is shined in the R eye, what is the direct response? consensual response?
absent direct response, normal consensual response
if there is a L oculomotor nerve lesion and a light is shined into the R eye, what is the direct response? consensual response?
normal direct response, absent consensual response
what is the near triad?
adjustment for near vision to maintain clarity of images at the fovea
1) accomodation reflex
2) pupillary constriction
3) convergence
is convergence conjugate or dysconjugate eye movement?
dysconjugate
what is the accomodation reflex?
the lens thickens from contraction of the ciliary muscles to adjust to near objects
what is the pathway of the accomodation reflex?
visual cortex–>oculomotor nuclei (midbrain)–>ciliary muscle
what is the pathway of pupillary constriction?
visual cortex–>oculomotor nuclei–> sphincter muscle
what is dysconjugate eye movement?
eyes moving in opposite directions
what is conjugate eye movement?
eyes moving in the same directions
what is the pathway for convergent eye movement?
visual cortex–>frontal eye fields –>CN 3
what are the age related pupillary changes?
pupils become smaller and sluggish
older adults can take more than 40 minutes to adjust to darkness
less flexible adjustment of the lens
what causes blown pupils?
CN 3 isn’t working to constrict the pupil bc the sphincter muscles aren’t innervated, so it stays dilated
efferent pupillary reflex isn’t working
increased intracranial pressure
BS damage
what causes miosis (excessive constriction)?
Horner’s syndrome
drug overuse
t/f: binocular vision requires image projection to corresponding point on both retinas
true
if image projection is not lined up in both eyes what occurs?
double vision
what structure is really important in L/R eye movement control?
the MLF!
how does the sup colliculus contribute to L/R eye movement?
via the MLF
what is the job of the MLF?
signals for head-eye movement coordination
BL connections among CN 3, 4, 6, 8, 11 nuclei
what is the result of an MLF lesion?
internuclear opthalmoplegia (INO) - lesion in the connection bw CN 3 and 6 contralaterally
can’t adduct one eye
eyes aren’t lined up=diploplia
what muscles need to be activated for conjugate eye movement?
lateral rectus and medial rectus
what muscles does CN 3 innervate?
levator palpebrae superioris
sup rectus
med rectus
inf rectus
inf oblique
pupillary sphincter muscles
ciliary muscles
what muscles are innervated by CN 4?
superior oblique
what muscles are innervated by CN 6?
lateral rectus
what is the role of the sup rectus?
eyes up
what is the role of the med rectus?
eyes medially
what is the role of the inf rectus?
eyes down
what is the role of the inf oblique?
moves adducted eye up and rotates abducted eye
what is the role of the sphincter muscles?
pupillary constriction
what is the role of the ciliary muscles?
increases the curvature of the lens of the eye
what is the role of the superior oblique?
brings the adducted eye down and rotates the abducted eye
what is the role of the lat rectus?
eye laterally
what is the result of a CN 3 lesion?
ipsilateral eye deviation out and down (can’t look in and up)
ptosis (droopy eyelid)
loss of pupillary constriction (enlarged pupil)
what is the result of a CN 4 lesion?
ipsi eye deviates up when adducted
no upward deviation unless adducted
what is the result of a CN 6 lesion?
ipsi eye deviates inward
eye can’t abduct bc of abducens and lateral rectus lesion
a lesion to what CNs can lead to diploplia?
CN 3, 4, 6
what causes diploplia?
misalignment of the eyes
will a chronic lesion have diploplia?
no, only acute, bc in chronic the eye will learn to block out images of one side
t/f: there is a loss of depth perception in chronic lesion bc of the lack of 2 visual fields
true
does a CN 3 lesion result in horizontal or vertical diploplia?
can be either or both
does a CN 4 lesion result in horizontal or vertical diploplia?
vertical (bc one eye is higher)
does a CN 6 lesion result in horizontal or vertical diploplia?
horizontal
does INO result in vertical or horizontal diploplia?
horizontal (bc one eye can’t abduct)
what is vertical diploplia?
eye is deviated upward and makes taking stairs difficult
what is horizontal diploplia?
eye deviated R/L makes it difficult to read
what are the 2 objects of eye movement?
direction of gaze and gaze stabilization
what are the components of direction of gaze?
saccades
smooth pursuits
vergence
what are saccades?
look quickly bw 2 images
what are smooth pursuits?
following slow motion like a moving train
tracking motions
what is vergence?
dysconjugate eye movements
what are the components of gaze stabilization?
VOR and OKR (optokinetic reflex)
what is the optokinetic reflex (OKR)?
physiologic/normal nystagmus
rapid eye movements
what are reflexive saccades?
unexpected movement mediated by the superior colliculus
what are voluntary saccades?
saccades involving more brain structures
frontal eye fields–> sup colliculus–> pons (PGC) and midbrain reticular formation–>CN 6, 3, 4
horizontal saccades result from stimulus from what CNs?
6 then 3
vertical saccades result from stimulus from what CNs?
3 and 4
what structures are involved in horizontal smooth pursuits?
CN 6 and part of CN 3
what structures are involved in vertical smooth pursuits?
midbrain reticular formation
CN 3 and 4
is smooth pursuits or saccades examined more by PTs?
smooth pursuits
what is the pathway for horizontal smooth pursuits?
visual cortex–>temporal eye fields–>frontal eye fields–> dorsolateral pons–>vestibular cerebellum–>vestibular nuclei–> CN 6 then 3
what is the pathway for vertical smooth pursuits?
visual cortex–>temporal eye fields–>frontal eye fields–> dorsolateral pons–>vestibular cerebellum–>vestibular nuclei–> midbrain reticular formation–> CN 3 and 4
what is nystagmus?
involuntary oscillating eye movement
physiologic or pathologic
what is the pathway of the optokinetic reflex?
pretectal area–>med vestibular nuclei–> oculomotor nuclei
what is vection? what is it important in?
illusion of movement/sensation of movement of the body in space produced by visual stim
VR games
is OKR physiologic or pathologic nystagmus?
physiologic
what are the 2 components of the OKR?
saccades and smooth pursuits
what does the VOR do?
stabilizes gaze on a target during fast head movement
when the head moves in one direction, which direction do the eyes move?
in the opposite direction
what is the pathway for the VOR?
head rotation–>SCC–>vestibular nuclei–>MLF–>oculomotor nuclei–>extraocular muscles
when the head rotates right, what extraocular muscles are activated?
lat rectus on the L
med rectus on the R
which visual stream is essential for saccades?
dorsal (action) stream
what are the areas essential for saccades?
frontal eye fields
dorsolateral prefrontal cortex
post parietal cortex
what are the frontal eye fields responsible for?
voluntary control of eye movements
what is the dorsolateral prefrontal cortex (DLPFC) responsible for?
preparation of saccadic eye movement
what is the post parietal cortex responsible for?
spatial info for eye movement
what visual stream is essential for the OKR and smooth pursuits?
ventral (perceptual) stream
what structures are essential for the OKR and smooth pursuits?
occipital and temporal eye fields
