Types , role and control of neural eye movements

Question 1

why do we have eye movements

Answer 1

to achieve clear and stable vision

so that the image is held stable on the fovea which allows for the best va

avoid oscillipsia whilst compensating for head movements

so that we stimulate both fovea simultaneously

binocular vision

steropisis

are eyes movement system is designed to move the two eyes together to look at the object of interest so that we get bincolar single vision and steroposis

Question 2

what are the two types of eye movement

Answer 2

those that keep the images steady on the retina e.g. vestibular collar , and optokinetic and smooth pursuit systems , there are also eye movement systems that change the line of sight to a new object of interest and hold it on the fovea e.g. saccades and vergence

Question 3

what does fixation entail

Answer 3

fixation i.e. keeping the eyes still is about holding the image steady on the fovea to achieve clear vision

because that is where there is the greatest density of photoreceptors

when the image moves from the central fovea you have a reduced va and oscillipsia (the image that we are seeing is not stable and it is actually wobbling)

we dont keep our eyes still all of the time there is a small amount of retinal motion called saccadic intrusions

when we slip from that slightly unstable motion to nystagmus that is when the oscillations are abnormal

that is when a another oscillation is happening and we possibly have nystagmus

so patients may report blur or oscillopisa or things moving around

Question 4

describe saccades

Answer 4

conjugate movement i.e. the eyes are moving together

fast - ballsistic

they are very brief and accurate to place an object of interest on to the fovea

dont interfere with vision - saccadic suppression e.g. when you are crossing a road and a car is coming down the road you move your eyes quickly to your periphery so that you can see the car but you dont see your eyes making the movement

voluntary (different stimuli)

on command

rem occurring during sleep

fast phase of the okr and the vor

Question 5

what are the features of saccades

Answer 5

latency (i.e. length of time before the saccade starts)

e.g. when has the object appeared and where have the eyes started to move

= 200m/s

velocity = 400- 700 degrees/sec

often reported as the peak velocity - how fast the eyes move when they are at there fastest

larger saccades have a higher peak velocity

Question 6

what is the saccade mean sequence

Answer 6

the bigger the movement - i.e. the more they have too move the faster they will move to get there

Question 7

describe the amplitude of saccades

Answer 7

amplitude referes to how far the eyes have to move to get from one target to another depends on the peak velocity

Question 8

what are you looking at in saccades when you testing accuracy

Answer 8

you are looking at accuracy

speed - i.e. are they slow at initiating the saccade

latency

you are also testing it horizontally and vertically

hypometric = often in small saccades (they undershoot the target)

hypermetric = they overshoot the target

Question 9

how do the eyes make a saccade

Answer 9

through a pulse and step process - this is the innervation that is ent to the eye muscles that gets them to a new position

there is a big pulse which makes the agonist muscle get to the new location

pulse gets the eyes to the new position - you dont want eyes to drift into the middle because you have lots of tissue in the orbit - the eyes are designed to be in the primary position so if you keep the eyes in the eccentric postion - they will drift back to the midline - so the step is the innervation that holds the eyes in there new position

Question 10

what happens to the antagonist and agonist muscles during the pulse step process

Answer 10

pulse = high frequency burst of activity

which happens to the agonist muscle which generates the forces needed and created a vicious drag

during the step process theree is a higher level of tonic innervation to the agonist muscle which holds the eye in its new position

and there are orbital elastic restoring forces

the antagonist muscle receives a reciprocal innervaion of change (i.e. the antagonist muscle must relax aswell)

Question 11

when a saccade is initiated how is its eccentric position maintained

Answer 11

there are a collection of neurone called the neuron integrators ( which are a distribution of neurone in the brainstem) - this helps to maintain eccentric gaze - neural integrator - integrates velocity and position to mathematically keep the eyes in that eccentric position of gaze

if you have a leak in your neural integrator you will not be able to maintain an eccentric position of gaze - the eyes will drift back to the middle and saccade

Question 12

what happens if you have a leaky neural integrator

Answer 12

unable to hold eccentric gaze position

eyes drift back to the centre

saccade back to the eccentric position

gaze evoked nystagmus

Question 13

what neurones are involved in saccades

Answer 13

burst neurons intikte the pulse (excitatory)

omnipause nuerons (inhibit the burst neruons)

Question 14

where are the burst neurones responsible for horizontal saccades situated

Answer 14

paramedian pontine reticular formation

pprf (horizontal saccades

rostral interstitial nucleus of the medial longitudinal fasiculus (rimlf) - vertical saccades

Question 15

what neurone are responsible for the holding the eyes in its eccentric position (step process)

Answer 15

the neurone that activate the tonic activity to maintain the eye In its eccentric position are in the nucleus prepostius hypoglossi for horiztonal saccades and for vertical saccades they are in the medial vestibular nucleus for horizontal gaze holding

interstitial nucleus of cajal is in the midbrain which is responsible for vertical and torsional gaze holding

Question 16

what is accuracy of saccades dependent on

Answer 16

age and fatigues - old people and babies

Question 16

what types of saccades can you have

Answer 16

you can have rudimentary reflexive saccades or higher level voluntary saccades the brain monitors accuracy and makes adjustments

e.g. for hypometric and hypermetric saccdes it will make an adjustment so that the eyes can reach the target

Question 17

when you record saccades what do you record

Answer 17

you can record where the abnormlaities are in the saccadic system e.g.

in the initiation , accuracy , velocity , pulse , step or a pulse - step mismatch

Question 18

what happens in the brain to get the signal to the eye muscles to make a saccade

Answer 18

there are 2 parallel pathways that converge In the brainstem one of the pathways comes from the frontal cortex and the other one comes from the parietal cortex

Question 19

what are horizontal saccades in control by

Answer 19

horizontal saccades are under contralateral control if you want to make a saccade to the left it is the right frontal eye field and the posterior parietal cortex that are sending that signal to saccade to the left the pathway decussates at the midbrain probably at the level of the 3rd cranial nucleus

Question 20

a saccade to the left is coordinated by which areas in the midbrain

Answer 20

right frontal eye fields and posterior parietal cortex

Question 21

a saccade to the left is coordinated by which areas in the midbrain

Answer 21

left frontal eye fields and posterior parietal cortex

Question 22

what are the two parallel pathways that converge in the brainstem responsible for

Answer 22

when the 2 parallel pathways converge - (the frontal cortex and the parietal cortex)

the frontal cortex pathway passes via the fef directly to the superior colliculus and also indirectly to the basal ganglia , its involved with self generated gaze changes to remembered anticipated or learned behaviour

the parietal cortex passes from the posterior parietal cortex to the superior colliculus

involved with shifting of visual attention to new targets that appear

Question 23

what are frontal eye fields responsible for

Answer 23

frontal eye fields initiate visually guided purposive saccades

Question 24

what is the dorso medial supplementary motor area responsible for

Answer 24

important in learned oculomotor behaviour

Question 25

what is the dorso lateral frontal cortex responsible for

Answer 25

the dorso lateral frontal cortex is responsible for the programming of saccades and attention shifts to remembered targets

Question 26

what is the role of the superior colliculus

Answer 26

contains a map to locate the eye to different areas of the visual field

Question 27

how is the thalamus , the basal glaglia and the cerebellum important in making the pathway for saccades

Answer 27

the thalamus is involved in the programming of saccades the basal ganglia is involved in thee initattion of voluntary saccades and preventing unwanted reflexive saccades and the cerebellum is involved in the control of saccadic accuracy and adaptive stuff(i.e. making adaptive changes if our eyes are not exactly where we need them to be)

Question 28

what are the components involved in the saccadic pathway

Answer 28

there are areas in the frontal cortex and in the parietal Cortex , there is a pathway going to the superior colliculus and ending up in the pons - making connections with the cerebellum - ultimately the pawtahy ends up in the brainstem making a saccade because we want a saccadic pulse

Question 29

describe the horziontal pathway for saccades

Answer 29

saccade begins in the left frontal cortex and the partial cortex the pathway is sent to the superior colliculus - it then deecussates to the other side and ends up in the right pprf (Paramedian pontine reticular formation) - i.e. the pulse generator for horizontal saccades if we want to saccade to the right we want our right lateral rectus and our left medial rectus to fire

Question 30

if you were to saccade to the right horizontally where does the impulse come from

Answer 30

the signal ends up in the right pprf and that sends excitatory burst neurones to the right 6th cranial nerve nuclei which sends a pathway from the 6th cranial nerve nucleus to the right lateral rectus - right lateral rectus innervates the right cranial nerve , from the 6th nerve signals also go from the mlf to the ipsilateral 3rd cranial nerve nucleus which innervates the left medial rectus - these are the excitatory burst neurone making the right lateral rectus fire and the left medial rectus fire

Question 31

when saccading horizontally to the right how are the antagonist muscles relaxing (i.e. how is the signal transmitted from the brain to the areas in the brainstem to ensure the eye muscles make the saccade)

Answer 31

from the right pprf - there are inhibitory burst neurones which inhibit the contralateral 6th nerve nucleus in the pons which makes the left lateral rectus relax and the right medial rectus relax which allows for a saccade to happen to the right

Question 32

what happens if you have a lesion in the pontine paramedical reticular formation

Answer 32

you will have ipsilateral saccadic paresis (saccadic palsy) ipsilateral saccadic paresis (saccadic palsy) paresis of ipsilateral conjugate gaze (gaze palsy) saccades/ pursuit/vestibular movements are affected

Question 33

if a patient is unable to make a saccade to the right what type of lesion do they have

Answer 33

a lesion can be localised at a level in or around the right pprf

Question 34

why is It important to test saccades in patients with 6th nerve palsies

Answer 34

if they have a ipsilateral gaze palsy - because the pprf is in close proximity to the nucleus of the 6th nerve

Question 35

describe the vertical pathway of saccades

Answer 35

you need bilateral stimulation of the frontal eye fields that signal ends up in the rostral interstitial nucleus of the MLF through posterior commissure to the cranial nerve nuclei it goes through the posterior commissure to the cranial nerve nuclei

Question 36

what is the posterior commisure

Answer 36

a rounded band of white fibres crossing the middle line on the dorsal aspect of the rostral end of the cerebral aqueduct connects the 2 cerebral hemispheres along the midline

Question 36

describe the downgaze pathway for vertical saccades

Answer 36

for downward pathways Impulse needs to go to the 3rd and 4th nuclei that innervate thee inferior rectus and the superior oblique

Question 37

describe the pawthay for up gaze saccades

Answer 37

pathway needs to go the 3rd narwal nerve nucleus to innervate the superior rectus and the inferior oblique

Question 38

where do the neurone originate and transmit to that ar responsible for vertical saccades

Answer 38

the excitatory burst neruons originate in the riMLF motor neurons in the 3rd and 4th nuclei in the interistial nucleus of cajal upward EBN projects bilaterally downward EBN projects ipsilaterally

Question 39

describe the pathway for vertical saccades

Answer 39

begins in the midbrain looking at the rIMLF and the INC to make a upward scare there are excitatory burst neurones sent to the 3rd and 4th cranial nuclir- they innervate the inferior oblique and the superior rectus the INC will get the contralateral superior oblique to relax and the ipsilateral inferior rectus to relax

Question 40

what happens if you have a lesion in the riMLF

Answer 40

it may have a mild effect on vertical saccades you will be unable to make ipsilateral torsional saccades if you have bilateral lesions of the rIMLF you will be unable to make vertical and torsional saccades

Question 41

describe the smooth pursuit movement

Answer 41

smooth tracking movement (object of interest must be kept on the fovea to ensure that the object of interest is maintained on/near the fovea velocity has to match the velocity of the target stimulus = movement off the fovea latency = 80- 120ms can be affected by drugs and age

Question 42

what is the role of the brain during smooth pursuit movements

Answer 42

during smooth pursuit movements the brain uses vision to monitor the performance of the smooth pursuit and it ig notes movement of background the brain can adjust smooth pursuits and the cerebellum is important in adaptation- if the eyes are going to slow/fast and aren't on the target the change in smooth pursuit can occur to ensure the eye is looking directly at the target

Question 43

what are the pathways hypothesised for smooth pursuits called

Answer 43

2 functional divisions of the visual system - they are detecting moving stimuli or what is happening to the object of interest (i.e. the features) in that vision of moving system = the magnocellular pathway - has retinal ganglion cells - m type and magnoceullaur layers of the LGN 4c alpha of primary visual cortex parvocellular pathway is involved in feature analysis contains retinal ganglion cells (p type) and parvocellular layers of the LGN layer 4c (beta) of the primary visual cortex

Question 44

from the visual cortex what areas are important for the response of moving visual stimuli

Answer 44

from the visual cortex the areas that are important the areas are in the striate cortex which projects to the middle temporal visual area - and the middle temporal visual area projects to the medial temporal visual area

Question 45

what cells in the visual cortex are responsible for smooth pursuits

Answer 45

in the primary visual cortex, v1 brodmann area 17 , striate cortex cells respond to moving visual stimuli striate cortex - projects to the middle temporal visual area , which is important in the processing of moving visual stimuli the mt projects to the medial superior and temporal visual area (MST) which is important for head and eye movement , the mt , most and posterior parietal cortex have connections with frontal eye fields and then the supplementary eye field in the frontal lobe

Question 46

describe the smooth pursuit pathway

Answer 46

descending pathways (originates in the parties - temporal occipital cortex) the pathway gets to different nuclei in the pons - e.g. the dorsolateral pontine nuclei and the nucleus reticular tegmenttai points from pontine nuclei tp cerebellum from cerebral,lum to pontine nuclei (adaptation happening - adaptive feedback) from the pontine nuclei to the 3rd , 4th and 6th cranial nerve nuclei

Question 47

describe the simplified pathway of smooth pursuits

Answer 47

detect that something is happening e.g retinal image motion - this goes to the lateral geniculate nucleus which then goes to the primary visual cortex from the primary visual cortex there is then a pathway that goes to the extra striate areas which sends signals to areas in the pons but also to the frontal lobe - you have adaptive feedback from the cerebellum and then the pathway ends up in the cranial nerve nuclei in the pons to make the Smoot pursuit

Question 48

what abnormalities occur in smooth purists

Answer 48

abnormalities in initiation , gain and symmetry unilateral lesions can cause a ipsilateral defect of smooth pursuit

Question 49

what is vergence

Answer 49

visual axes of the image object - interest falls on both fovea smulatenously disjugate movement - i.e. the eyes are moving in an opposite direction e.g. convergence , divergence , vertical vergence and cyclovergence when vergence fails the patient will report diplopia and confusion - when vergence fails patients= symptomatic

Question 50

what is vergence driven by

Answer 50

retinal image disparity and retinal image blur disparity = a stimulus for fusional vergence movements and blur is a stimulus for accommodative vergence movements accomodation of lens pupil constrictiion

Question 50

describe the speed of vergence

Answer 50

vergence is a slow movement - we have to encourage the patient to do it blur driven vergence = 200m/s reaction time disparity driven vergence= 160m/s reaction time 3/12old neonatal misalignments 45 yrs old (slower vergence)

Question 51

describe vertical vergences

Answer 51

vertical prism fusion range improves with practice , - however they are slower and a lower range of amplitude than a horizontal movement extended in longstanding vertical deviations e.g. in patients with TED

Question 52

describe the vergence pathway

Answer 52

visual signals (e.g. blur and retinal disparity) visual signals from the occipital cortex goes to the mesencephalic reticular formation (midbrain) - that projects to the 3rd cn nucleus - different cells respond to different types of movement pro[osed tha other cells are involved in vergence e.g mergence neural integrator, vergence tonic and burst cells

Question 53

abnormalities of conergence

Answer 53

erg, convergence insufficiency / paralysis divergence paralysis spasm of near reflex

Question 54

what is the vestibular ocular reflex

Answer 54

relates to keeping vision steady and gaze steady even though the head is moving dolls head movement is when the eyes are moved I n an opposite direction to the head movement but at the same speed e..g head movement to the left , eye movement to th =e right fast movement with a short latency use vision to monitor the accuracy of the movement cars indendeptly of visually mediated eye movements

Question 54

how does the brain detect that the head is moving

Answer 54

vestibular system - inner ear hair cells and fluids in the ear that detect movement difff structures in the ear detect head movement and send neural impulses to the vestibular nuclei

Question 55

what structures in the ear detect head movements

Answer 55

peripheral vestibular apparatus linear movements. transitional vor otolith organs (utricle and scull) rotational movements angular vor 3 semicircular canals on the inner ear specialised hair cells convert mechanical forces into neural impulses - inputs are sent to the vestibular nuclei

Question 56

what are the 2 pathways for the vestibular ocular pathway

Answer 56

the pathway goes via the cerebellopontine angle and ends up in the vestibular nuclei which then project to the 3rd, 4th and 6th nuclei , the different canals in the head detect different types of head movement and initiate different types of eye movement - depending on where that eye movement comes from determines which signals get a movement

Question 57

which part of the ear is responsible for upward and torsional eye movements

Answer 57

anterior semicircular canal (Ipsilateral superior rectus and contralteeral inferior oblique) posterior semiccircular canal is responsible for downward and torsional eye movements (ipsilateral superior oblique an d contralateral inferior rectus's) lateral semicircular canal is reesponsbiblee for horizontal eye movement s 9ipsilateral medial rectus and contralateral lateral rectus

Question 58

what other parts of the brain are responsible for the vestibular ocular pathway

Answer 58

vestibular. nuclei also receive projections from other brainstem nuclei , cerebellum and cerebral hemispheres central role in generating compensatory eye movements (head movement) adaptation

Question 59

what ar symptoms of vor abnormalities

Answer 59

disorders of vor can cause changes in gain , are and or balance common signs / symptoms disequilibrium unsteadiness vertigo nystagmus blurred vision oscillopsia(particularly with head movement)

Question 60

what are features of vestibular nystagmus

Answer 60

it will only be present in the dark where there are no visual stimulus peripheral and central vestibular lesions can result in vestibular nystagmus- test with and without visual fixation - peripheral vestibular lesions - mixed vertical and torsional nystagmus central vestibular lesions (purely vertical or purely torsional nystagmus)

Question 61

what is caloric stimulation

Answer 61

irrigating the ear with different temperatures f water to try and initiate different eye movements used to try and compare the response to different tempretures of water using it to investigate acoustic nerves cold water in ear - eyes beat in opposite direction warm water eye beat in the same direction

Question 62

what is an optokinetixc response

Answer 62

slow following. movement (pursuit) and a fast re- fixation (saccade) in the opposite direction only present if afferent visual pathway to cortex and connections to brainstem ocular motor system are intact

Question 63

when does a optokinetic response occur

Answer 63

occurs during sustained self rotation/sustained movement of the visual envrioment (own drum)/ full field stimulus persists after stimulus has ceased optokinetic after nystagmus

Question 64

what is the ateiology of latent nystagmus

Answer 64

accessory optic pathway

Question 65

what is the pathway of the optokinetic response

Answer 65

pathway unkown important areas are MT OR MST

Question 66

what is a vestibular ocular reflex

Answer 66

holds images of the seen world steady on the retina during head rotation direction = conjugate and the control is vestibular and the speed is slow

Question 67

what are optokinetic eye movements

Answer 67

holds images steady on the retina during sustained head rotation direction = conjugate control is supra nuclear and the speed is slow

Question 68

what are smooth pursuit eye movements

Answer 68

holds images of a moving target on the fovea , direction = conjugate control = supranuclrar and the speed = slow

Question 69

what are saccadic eye movements

Answer 69

brings objects of interest onto the fovea , the direction= conjugate and the control = supranuclrar and the speed = fast

Question 70

what are vergence eye movements

Answer 70

when the eyes move in opposite directions so that the images of a single object are placed on both fovea it is a disjugate movement and the control is supranuclear and the speed is slow

Question 71

what are nystagmus quick phase movements

Answer 71

directs the fovea towards the oncoming visual scene during self rotation resets the eyes during prolonged rotation conjugate movement control is supranuclear speed = fast