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236 Cards in this Set

  • Front
  • Back
5 major eye movements
OKN
VOR
pursuits
saccades
vergences
What deters retinal slip?
VOR
OKN
What eye movements let you change the angle of gaze?
pursuits
saccades
vergences
What prevents fading of visual images?
microsaccades
drifts
tremors
When you feel as if the world is moving it is called
oscillopsia
What type of nystagmus do people tend to notice more visual problems: aquired or congenital?
Aquired

Congenital nystagmuses give the brain more time to adapt to retinal slip.
Aquired nystagmus, like in MS, occurs later in life and more people have difficulties adapting
When do VOR and OKN begin to develop?
At birth
At what age do saccades develop?
At birth
At what age do pursuits begin and develop?
6-8 weeks
At what age does vergences, accomodation, and binocular vision begin and develop?
3 months
What is the orbital plant?
The "apparatus" within the orbit: tissue, EOMS, neurons, cortex, brainstem, etc
Strabismus can occur due to what two things?
muscular OR neural control
What is viscous drag?
The resistance that must be overcome to initally move the eye
What is elastic restoring forces?
Occurs when the eye is displaced, it is the force needed to be overcome in order to move eye to a new position
Pulse signal
the PHASIC increase in neural activity.
Allows the EOM to overcome VISCOUS drag
What overcomes viscous drag?
Pulse/phasic signal --> burst of neural activity right before eye moves to give it the necessary push
Step signal
SUSTAINED increase in neural acitivty, allows EOM to work against the ELASTIC FORCES of the orbit tussue
What overcomes the elastic forces of the eye?
Step/sustained signal
__________ firing leads to the movement of the eye followed by a ________ signal to the muscle in order to maintain the new position
Pulse

Step
Without pulse, eye movement is _____
slow
Without step, eye position cannot be ____
maintained
Where is the problem located for internuclear opthalmoplegia?
Lesion is located at MLF. Information does not go from one side of the brain to the other.

Abducens nerve cannot cross MLF to send signal to contralateral 3rd nerve. This decreases PULSE signal.

NOTE: INO is a CONDUCTANCE problem, not a faulty pulse or step signal
What kind of problem is gaze- evoked nystagmus?
cerebellum

Eye gazes to one direction (left or right). Tell patient to look right. Patient gazes to right and see end pt. nystagmus with eye jerking to the left. When told to look centrally, there is a REBOUND effect where the eye will then nystagmus to the direction originally told to look (in this case, to the right)

http://video.google.com/videoplay?docid=83290528059760181
Is end point nystagmus abnormal or normal?
normal
Internuclear Ophthalmoplegia
There will be horizontal diplopia in lateral gaze. The patient will manifest an adduction deficit on the involved side and a nystagmus of the fellow eye in extreme abduction.
For example, for a patient to gaze to the left, the left supranuclear control center of horizontal eye movements [paramedian pontine reticular formation (PPRF)] must signal the left CN VI nucleus to turn the left eye outwards. At the same time, the PPRF must signal the right CN III nucleus, via the right MLF, to simultaneously turn the right eye inwards. A lesion of the right MLF would not allow the neural impulse to reach the right medial rectus. In this case, the left eye would abduct, but the right eye would not adduct. Further, the left eye would go into an abducting nystagmus.
http://content.lib.utah.edu/cdm4/browse.php?CISOROOT=/ehsl-shw
SPINOCEREBELLAR ATAXIAS
See nystagmus when gazing in either direction: right or left. And then see REBOUND when looking centrally
Wernicke's Encephalopathy
--> Lack of Vitamin B, seen in alcoholism.
See abnormal eye movements/nystagmus
T/F Eye movements can undergo adaptation changes
True

When you get new glasses, you need to adapt your VOR due to magnification changes
What plays a large role in motor plasticity? And what parts are most involved?
Cerebellum

Flocculus, nodulus, dorsal vermis
2 Prerequisites for eye movements?
Orbital plant AND neural signals
Afferent system for accurate eye movements provides info for?
Tells brain about the position of the is located with respect to the head.
There are two sources for the afferent system: proprioception( from muscle spindles and palisade tendon organ)
Efference copy (duplicate copy of the motor signal to move the eye that is sent back to brain)
2 sources of afferent system?
1. Proprioception involving the muscle spindles that respond to stretch AND the palisade tendon organs that respond to tension

2. Efference copy: the duplicate copy of the motor signal to move the eye that is sent to the brain.
Efference copy is part of the ______ system
afferent
Efferent system for accurate eye movements provides info for?
Tells the brain where and by how much to move the eye= how much PULSE and STEP signal to generate
Ocular Motor nuclei involved in controlling EOM movements?
3,4,6
Oculomotor nuclei controls
medial, superior, inferior rectus and inferior oblique.

It also controls levator, pupil size, accomodation and lacrimal gland
Abducens nuclei controls
lateral rectus
Trochlear nerve controls
Superior oblique
Twitch fibers
receive pulse signal! All or nothing action potential.
Are FAST-fatiguing fibers.
Known as GLOBAL fibers.
GOOD for rapid movement of the eye to new position
What are GLOBAL fibers?
Twitch fibers, all or nothing action potential, pulse signals
Non-twitch fibers
Tonic/STEP receivers.
These have graded contrations, high oxidative capacity.
Are known as ORBITAL fibers.
These are good for maintaining new eye positions.
Wat are ORBITAL fibers?
Non-twitch, graded, step signals
What is the Center of rotation?
NOT a fixed point inside the globe, but a locus of points known as the SPACE-CETROID OR BODY CENTRODE.
Reason for why there is no center of rotation?
Due to the fact that eye rotation is also accompanied by small TRANSLATIONAL movements.
Fick's axes:
X
Y
Z
X is --> LEFT to RIGHT

Y is --> FRONT to BACK

Z is --> UP and DOWN

Picture this from a TOP view of someone's head. (like placing an X-Y-Z axis on a a bald man)
Duction means
rotation of ONE eye
Duction axes:
X
Y
Z
X= elevatation or depression

Y= intorsion or extorsion --> cylorotation

Z= abduction and adduction --> looking laterally

Picture X_Y_Z axis and the eye rotating AROUND the axis
True torsion
Rotating around Fick's Y axis
Equator definition
circumfrence of eye that represents a locus of points equidistant from the ANTERIOR and POSTERIOR poles of the globe.
Listing's plane defintion
= Equatorial plane of the globe.

It is PERPENDICULAR to the fixation line in primary gaze.

It is defined as Fick's Z axis (going straight up and down)
Primary position
look straight ahead into the distance
Secondary position
Look up-down AND right to left.

Rotation around Z or X axis
Tertiary position
All oblique cobinations of up-down and right-left together. (Somewhere between X and Z axis)
This is FALSE torsion.

True torsion is rotation around Y axis alone
Muscle plane
2 lines joining the center of rotation at the MUSCLE axis.
What wraps around the eye and anteriorly attaches to the wall of the orbit?
Tenon's capsule, and the attachment to the wall is the CHECK ligament.
Superior check ligament
Whitnall
Inferior check ligament
Lockwood
Nasal check ligament
medial
Temporal check ligament
Temporal
Check ligament defines _______
the limit of eye rotation, affects the field of fixation
Anatomical insertions
physical point of insertion of EOM to the eyeball
Physiological insertion
point on the muscle that TANGENTIAL to the eye, where the torque of the muscle acts to rotate the globe.
Arc of contact
Angle created where the anatomical and physiological insertions points are connected to the center of rotation
Action of medial rectus muscle in 3 positions
adduction
Actions of lateral rectus muscle in 3 positions
abduction
Actions of inferior rectus muscle in 3 positions
depression, extorsion, adduction
Actions of superior rectus muscle in 3 positions
elevation, intorsion, adduction
Actions of inferior oblique muscle in 3 positions
extorsion, elevation, abduction
actions of superior oblique muscle in 3 positions
intorsion, depression, abduction
Superior muscles ______
INTORT
Oblique muscles ________
ABDUCT
Inferior muscles _________
EXTORT
CARDINAL positions: H figures
OD OS
SR IO IO SR
LR MR MR LR
IR SO SO IR
How to isolate SR muscle
look out 23 degrees
How to isolate SO muscle
Look toward nose by 54 degrees
Sherrington's Law of reciprocal innervation
Increased activity in one agonist EOM has equal decreased activity in the antagonist muscle.
So to look to the right:
OD eye has innervation of Right LR and equal decreased activity of Right MR
Hering's law of equal innervation
Equal and simultaneous innervation is given to syngeristic/agonist EOMS.
These are YOKED muscles!

So if you want to look to the Right, there is equal stimulation to the Right Eye Lateral Rectus and the Left Eye Medial rectus
Fick system of torsion
horizontal movements followed by vertical eye movement= Rotation around the Z axis followed by the X axis
Helmohltz system of torsion
Vertical followed by Horizontal movements. Rotation around the X axis followed by rotation around the Z axis
Donder's Law on rotation of tertiary position
depends upon the horizontal and vertical gaze angles, IRRESPECTIVE of how eye reaches position. Requites TWO seperate movements
Listing's Law on rotation of tertiary position
Rotation about the Listing's plane. Movement on one axis causes the eye to move to that position in ONE single movement.
Foveal fixation to a peripheral object is accomplished either:
moving the eyes alone OR moving the eyes and head together.

The eyes tend to move alone only when the field of fixation is less than 15 degrees away (reading at near)
Field of fixation=
how much the eye can rotate with the object of interest still on the fovea
T/F Monocular field of fixation is greater than binocular field of fixation
True
T/F The ability to rotate the eye changes drastically with age
False
The monocular field of fixation is roughly______ and the binocular field of fixation is roughly_______
30-40 degrees

60-100 degrees? according to NTS
1. Monocular field is limited by______


2The binocular field is limited by _______
1. part of the orbital plant, mainly the check ligaments and Tenon's capsule

2. Te the ability to maintain bi-foveal fixation
Diagnostic field of action of eye movementsi s tested using:
Ductions
Versions
Saccades
Pursuits
Vergences
Nystagmus
Phoria/Tropia

Note: ductions and versions are the same eye movements exception DUCTIONS are monocular and versions are BINOCULAR
When conducting ductions or versions, what would you expect a normal patient NOT to report?
Double vision/diplopia, pain
When conducting ductions or versions, what happens when the target excursion is too large?
End point nystagmus or head movement
When conducting ductions or versions, what do you look for?
Underaction/restricted action and overaction of the EOMS
If patient is looking to their nose you are testing which muscles?
Obliques
1. Abnormal small amplitude saccades suggest __________ disorder

2.Abnormal large amplitude saccades suggest ___________ or _____ disorders
1. central neural

2. peripheral neural or EOM
The Supranuclear center of the brain gives the signal for:
VOR
OKN
saccade
fixation
pursuit
vergence
1Nuclear and infranuclear centers=

2. This is the "Final common pathway that receives ______________ signals
1. CN 3, CN 4, CN 5


2. pulse and step

Dirsoders here are "nerve palsies"
Oculomotor nerve palsy lesion results in and occurs due to?
dilated pupil, stabismus (up abd out eye), partial ptosis.

Can occur with pituitary tumor supressing CN 3
Abducens Nerve Palsy results in
problems abducting eye, possible esotropia.
Trochlear Nerve Palsy results in
SO disfunction
Parks-Bielchowsky 3 step test for vertical deviations:
During each step, patient looks at certain direction and CT is done.
Step 1: PRIMARY gaze--> what position is the eye?
Step 2: LEFT and RIGHT gaze --> where is there more deviation
Step 3: LEFT and RIGHT head tilt --? where is there deviation?
How does the visual system compensate for undesirable retinal image movement?
VOR and OKN are compensatory eye movements

The INITIAL eye movement is VOR
For VOR, the eye postion of the orbit and the head position in space are in _______ directions in roder to remain a stable retinal image
opposite
The ____ phase eye rotation in VOR is the _____ direction to head roation to compensate for ead movment
slow

opposite
the slow phase of VOR is in the SAME direction as ________
"perceived motion"
VOR is created when _________ are stimulated
semicircular canals.

Thus, the INNER ear controls VOR.
NOT visual imput
T/F VOR occurs even when eyes are closed
True
VOR is initated _____ msec after the semicircular canals are stimulated
16 msec
OKN is initiated ______ msecs after visual image motion
70 msec
OKN --> optokinetic nystagmus
Is induced by?
bisual input
Translational vestibular ocular reflex is induced by
linear/translational head movments by stimulation of the otoliths (UTRICLE)
Ocular counter rolling is induced by the stimulation of the
otoliths (SACCULE) during static head tilt
Cervico-ocular reflex is stimulated due to
somatosensory stimulation (head and body movements)
VOR Three Neuron Arc Circuitry
Angular acceleration stimulates
1. Semicircular canals, which stimulates
2. Vestibular nucleus, which sends a signal to the brainstaim generating a pulse and step signal sent to
3. Ocular motor neurons, leading to the VOR
The slow phase of VOR is known as the ___________ movement and the fast phase is known as the _________ movement
compensatory eye movement

saccadic eye movement (THIS IS NOT VOR)
Doll's Eye Testing tests
VOR. If VOR is good, then the brainstem is well developed.

When you quickly rotate pt. head to the right, a good VOR should be observed.
If you rotate head and you see jerky eye movements, saccadic eye movements are being used INSTEAD to overcome the retinal slip.--> pt. will often complain of vertigo and tinnitis.
VOR occurs with _________ frequency head while OKN occurs with ______ frequency head rotations
fast

slow
OKHN moves in the direction of the
actual stimulus motion.


(moves in the same direction as VOR)
To produce VOR and OKN at the same time, test with
lights on/eyes open, head rotation.

If its dark, only VOR will occur.
Post Rotational Nystagmus is
the after effect of VOR
Optokinetic after nystagmus is
the after effect of the OKN
What stops the residual eye movemnt at the termination of ration, thus preventing vertigo and dizziness from occuring?
OKAN cancelling out the PRN
The slow phase of PRN is the ___________ of the slow phase of VOR
opposite

Therefore PRN is in the same direction of head rotation
OKAN is in the ________ direction of OKN
same direction

Therefore OKAN occurs in the opposite direction of head rotation/ same direction as VOR
TVOR (Translational Vestibular Ocular Reflex)is tested using:
Head Heave response (tests translational movement)

Head Impulse test (tests rotation)
Which compensatory eye movement is NOT stimulated by the vestibular system?
OKN --> visual
Gain=
the output (the VOR-eyemovement) divided by the input (head roation)

If =1, there is perfect compesation and output=input
If <1, output is less then input and a SACCADIC eye movement occurs since VOR is not perfectly cpensating retinal slip
If Gain=1
If =1, there is perfect compesation and output=input
If Gain <1
If <1, output is less then input and a SACCADIC eye movement occurs since VOR is not perfectly cpensating retinal slip
Phase=
Temporal synchrony.

The system is IN phase wen the slow phase of VOR is EQUAL and OPPOSITE of head rotation.

The system is OUT of phase when the slow phase of VOR is less than that of the head rotation --> causes a reduction in gain.
For a perfect compensatory action

1.Phase DIFFERENCE=

2. Phase SHIFT=
180 degrees


0 degrees!!
For perfect compensation and accurate eye movement,
gain= ________ and the phase difference is _________, while the phase shift is __________
1


180


0
time constant=
time it takes for the eye velocity to decline to 37% of the einitial value.

It is how soon the eye movement comes to a stop.

The LARGER the Tconstant, the LESS the phase shift, the BETTER the compensation
The CLINICAL equivalent of gain, phase, and time constant=
accuracy
speed
smoothness
The LARGER the Tconstant, the LESS the phase shift, the BETTER the compensation clinically means=
The smoother the eye movement, the faster the eye movement, the more accurate the eye movement.
If gain is low then
phase shift is larger
If phase shift is large then
the Tconstant is small, the smoothness of the movement is decreased.

If phase shift is large BUT the speed or frequency of the head rotation is slow we have a BAD stimulus to VOR (VOR works with HIGH frequency movements). We do, however, have a GREAT stimulus for OKN.
Factors that effect VOR gain
Proximity of target. (Gain increases with a near target)

Attentiveness of subject

Change in Spec Rx due to magnification effect


Visual input, which effects the arc at the vestibular nucleus
If left to MECHANICAL prperties of semicircular canal, VOR Tconstant would be=________
However, OBSERVED VOR Tconstant is _______
6 sec


15-20 sec
Velocity storage mechanism of VOR is
the process in the brain --> VESTIBULAR nucleus, that PROLONGS the Tconstant from 6 to 15 sec.
It acts like a battery charging up for the stimulation and it gives RISE TO THE OKAN, which helps neutralize the PRN after effect.
Factors that effect VOR time constant=
1. Habitutation (adaptation of stimulus decreases VOR generated)
2. Early visual deprivation
3. Age (reduced Tc in young)
4. Head tilt
5. Peripheral vestibular disease.
If angular acceleration is ___________ then no VOR is produced since semicircular canals aren't stimulated
0

velocity is constant
When subject feels a sensation of self rotation, it is known as
circularvection
When responding to a moving stimulus, the visual system first generates _______ but then OKN takes over
Pursuits.

You first follow the drum target until brain realizes the repetition of the spinning drum and OKN takes over.
OKAN is generated by__________ and helps to neutralive the ____
the velocity storage mechanism


PRN
T/F You can see your patient produce OKAN
False

When subject is in a lighted environment you cannot see OKAN because visual fixation cues mask it.
VOR and hyperopic lenses
Magnification causes an INCREASE in gain of VOR.

Gain increases due to the larger angle the eye will need to rotate
VOR and myopic lenses
Needs to reduce gain of VOR, eye rotates less.
If you rotate subject horizontally but make them view a vertical stimulus then the VOR will be
vertical
T/F Cognitive input can effect the gain of VOR
True

Imagining a stationary environment while being spun around can effect your VOR
The Nucleus of the Optic Tract in the pretectal region of the midbrain is an inportant sturcture in the generation of _____
OKN
Rotation of the head causes retinal slip, which the brain overcomes by generating ___________

Retinal image motion causes retinal slip that the brain overcomes by generating ________
VOR


OKN
Sustained rotation in the DARK
- VOR will occur at the start of rotation, however, once it reaches a constant velocity, VOR will stop.

- OKN will NOT occur because there is no visual input.

- OKAN will NOT occur, either.

- PRN will occur and come to a stop after the constant velocity occurs.
Sustatined rotation of an OKN drum
- VOR will occur at start of rotation but will stop when accelration is 0
- OKN will occur as a result of the repetitive motion stimulus
- If light is turned off, we can see OKAN (however if light is still on, OKAN will be masked)

- PRN will occur
At the vestibular labyrinth, what anatomical parts are present?
The semicircular canals are present and VOR is stimulated due to rotational head movement.

The endolymph is the fluid inside the canals.

The crista ampulla are enlargements at te ends of the canals containing receptors

- The ampullar crest is covered by the cupula that fills the space of the ampulla. The hair cells are embedded in the cupula.

- Each hair cell consists of one long kinocilium and multiple sterocillia.

- The ampullary nerve carries the signal regarding head rotation from the semicircular canal's ampulla to the vestibular nucleus.
What are the otolith organs?
The uturile and saccule.
TVOR stimulation is due to translational head movement --> utricle
Ocular counter rolling stimulation is due to static head tilt --> saccule
How is the signal regarding head rotation generated by the semicircular canals?
Endolympj inside moves and flows in the OPPOSITE direction of head rotation. It pushes on the cupula and bends the hair cells to create an ELECTRICAL signal.

Bending towards the kincilium is excitation/depolarization of vestibular nerve.
Final output of the semicircular canals
generation of a head eelocity signal through the process of MECHANICAL integration (not in the brain) where the head accleration signal is MECHANICALLY integrated into a head veloicty signal.

Remember, Semicircular canals= mechanical signal
What carries the Head velocity signal information?
neural signals exciting the semicircular canals.
The semicrulcar canals allow te motion of the endolymph to be proportional to ______--
head velocity.

If you icnrease accerlation, then more endolymph flows with greater force and a greater head velocty is produced.
T/F kinocillia face the utricle/a,pulla so that endolymph that flows toward the ampulla is excitatory
True

The orientation is the opposite in the two vertical semicularuc canals.

Endolymph flow toward the ampulla is INHIBTORY in the vertical semicircular canals.
T/F The output in one eear is excitatory while the output in the other ear is inhibitory, which allows a push pull arrangment that synchronizes conjugate movements in the two eyes
T
An ear infection causes
an unequal signal sent from both ears. VOR will not be well compensated. This can lead to a possible nystagmus.
Vestibular nucleus complex generates?
Eye velocity/pulse and eye position/step signals
The eye velocity/pulse signals is generated by the vestibular nucleus from the _________ signal
head velocity .
What two nuclei are responsible for all integration of HORIZONTAL conjugate eye movements? (This will probably be a test question)
Medial Vestibular Nucelus and the Nucleus prepositus hypoglossi
The nueral integrator of the eye velocity signal is the ________ for all VERTICAL conjugate eye movments? (This will be a test question)
Interstitial nucleus of Cajal
For HORIZONTAL VOR, the vestibular nucleus provides signals to the ________ aducens nucleus and the ______ oculomotor nucleus
(This may be a test quetsion)
CONTRALATERAL

IPSILATERAL
What do the otolith organs contain instead of endolymph?
CaCO3 crystals

A signal is generated based on te tilt of the crystals (works the same way as endolymph in terms of exciting and inhibitng towards and away from kinocilium.
Basic OKN pathway found in all animals
Retinal input is sent to the
1. Nucleus of the Optic Tract (NOT) to the
2. Accessory Optic System (AOS, which is sent to
3. 2 Neural integrators: Vestibular nucleus and nucleus prepositus hypoglossi, which thus produce

OKN
OKN pathway found in higher animals
Retinal input is first sent to
1. Visual cortex via lateral geniculate. From here, the info is sent to
2. Nucleus of Optic Tract and Accessory Optic System, which then sends the info to
3. Neural integrators= Vestibular nucleus and nuclear prepositus hypoglossi to produce

OKN
In INFANTS AND AMBLYOPES:

OKN is better compensenated when movement is from the ___________ direction
Temporal to nasal

The temporal nasal direction is superior with better compesnated OKN because it is DIRECTLY processed by the basic pathway.

The nsal temporal direction is INFERIOR because it is first processed by the visual cortex via the additional higher order pathway.

In NORMAL adults --> there is symmetry between the two directions and the cortical pathway predominates both --> processing in both temporal-nasal and nasal temporal motion are mainly performed by the visual cortex.
T/F

In NORMAL ADULTS, OKN is better compensenated when movement is from the temporal to nasal direction
False

In NORMAL adults --> there is symmetry between the two directions and the cortical pathway predominates both --> processing in both temporal-nasal and nasal temporal motion are mainly performed by the visual cortex.
Your amblyopic patient exhibits OKN asymmetry. Where has the mal-development occurred and what is the treatment?
The visual cortex, specifically in potion processing.

Vision therapy can be done to train eyes, first correct patient to best corrected VA
Circularvection occurs because
OKN information goes through the vestibular nucleus to produce pulse and step signals, which is providing and receing info to and from the sensory cortex at the same time.
The ability to distinguish between self motion and envionmental motion is by way of which nucleus?
vestibular
Central vestibular disorders occur in the _____
brain.

All other disorders are "peripheral"
Rotational vertigo is due to
a problem within the semicircular canals or central projection of canals.
Sensation of body tilt is a problem with
the otolith system
Testing vestibular function using: Static imbalance
Patient is station and fixates at a distant target --> check for gaze stabilization. If nystagmus is present, fixation is not steady.

During DO, you can see movment of the optic nerve, indicates nystagmus is present.
Testing vestibular function using: Dynamic imbalance --> 2 manuvers used
1. Vigorous, sustained head shaking for 10-15 sec --> if nomral, once shaking stops, you do not see much nystagmus. If nystagmus is observed, it indicates an imbalance in the vestibular tone between the two ears (one has a lesion)

2. Single rapid head turns --> gaze will be stead if VOR is normal, and if not, a corrective saccade is required to stabalize gaze.
Positionally induced imbalance --> dix-hallpike maneuver
Turn head 45 degrees to right ro left, bring patient to supine position below horizontal and look for nystagmus, when it ends, bring patient back upright and check for nystagmus again.
Treatment involves the Epley manuver
Tullio phenomenon
nystagmus whenever you hear a certain sound
Caloric testing --> BOARDS loves it
Patient lays down with head elevated 30 degrees from horizontal. Warm or cold water is placed in the ear to induce convention currents within the endolymph, depending on water temperature

1. Warm water= flow TOWARDS ampulla, causing excitation
2. Cold water= retraction of endolymph, causing inhibition.

To test vertical canals, patients head is lowered from horiztonal by 60 degrees.

COWS --> Cold Opposite, Warm Same (as the fast phase of nystagmus) --> opposite of the usual way we think of VOR

note: fast phase is produced by the pontine paramedian reticular formation --> causes horizontal saccades
Caloric testing in comatose patients
you dont see a fast phase because the FRONTOPONTINE connections are not functonal.
You see slow phase because the nuclear and infranuclear connects are intact
Jerk nystagmus
well defined also and fast phase

usually found in amblyopia
Pendular nystagmus
no defined fast phase

Can occur due to foveal disoders, or loss of fixation reflex.
Latent nystagmus manifests if you
occlude the better seeing eye, due to reduced fixation.
Null point=
certain eye and head position which minizes nystagmus --> find it by doing versions. Then use prisms to shift the image to the null point
For nystagmus treatment, use BASE OUT prism if
convergence is found to reduce nystagmus
For nystagmus treatment, use yoked prism if
extreme head turn reduces nystagmus. Put the base towards the null point to reduce head turn
T/F You put the BASE of the prism towards the null point to reduce head turn
true

put base in the direction you turn your head
Problem: head turn to the right, eye turns to the left.
Solution:
Solution: base right prisms reduce head turn to right
Direct ophthalmoscopy/Visuoscopy
Stability of fixation and to determine fixation is central or eccentric.
Do DO with spider web pattern.
Three criteria for constructing an eye tracking instrument
index of measurement
a measurement device/detector
amplifying device
Electro-oculography EOG
index of measure: electric potential difference as the direction of gaze changes

Measurement device: electrodes
Amplifier: computer
Infra-red tracking device:
Index of measurement: IR reflected from iris and sclera
Measured using: IR photodetector, photcell in goggles that measure reflectance.
Amplifier: computer

good for peds
Purkinje image tracker
index of measure: purkinje image OR reflected white light from cornea
measured using: static photographic or dynamic video
amplifier: computer
Sclera contact lens optical level tracker
BEST test for researchers!!!

index of measurement: light reflected off a mirror attached to CL
measured using: video camera
amplifier: computer
Sclera contact lens: magnetic search coil
GOLD STANDARD FOR MEASURING EYE MOVEMENTS

index of measurement: change in electrical voltage.
measuring device is a wire in CL
amplifier: computer
GOLD STANDARD FOR MEASURING EYE MOVEMENTS
Sclera contact lens: magnetic search coil
the vestibulocerebellum (floccus and nodulus) controls
pursuits and VOR
THe dorsal vermise of the cerebellum controls
saccades
"for the sake of simplicity" the center of rotation of the eye is a fixed point that lies
13.5 mm behind the corneal apex and 1.6 mm to the nasal side of the geometric center of the bloge
Superior rectus makes an angle of _______ in primary position
23-25
Inferior rectus makes an angle of _______ in primary position
23
Superior Oblique makes an angle of _____________ in primary gaze
51
rotate OKN drum with stries oriented vertically, the fast and slow phases of OKN are?
slow phase follows the stripes down
fast phase= eyes move back up
As you increase speed your OKN....
increases, but at higher speeds, it begins to break down and VOR is stimulated
After the subject experiences OKN for awhile, stop the drum rotation, is OKAN 1 present?
It is present but it cannot be seen because presence of visual cues mask OKAN
initate OKN on a subject with one eye occluded, experimenter looks behind occluder, is the occluded eye undergoing OKN as well?
YES
If you actively follow the rotating drum, is this a true OKNN?
No, you follow the stripe using PURSUITS
After spinning patient clockwise, we observe an eye movement, which one? What are the fast and slow phase direction?
PRN

Fast is right to left
Slow is left to right.

Anticlockwise spinning would lead to: Fast left to right, and Slow right to left.
Definition of practical field of fixation
when fixation is achieved by both head and eye movements
reflexive saccade
generated to a novel stimli that unexpectedly occurs within the environment
Volitional saccade
can be predictive/anticipatory
can be generated on command
can occur to move eyes to a remembered target (like a clock)
spontaneous saccades
seemingly random saccades that occur when subject is not required to perform any specific task
1. End point of convergence
2. End point of accomodation
1. diplopia, eye turn

2. Blur, increase in pupil size
fixation during reading....
refers to the total number of eye stops or pauses of the eye during reading, the more difficult the material, them ore fixations are made. POOR readers make more fixations than good readers
Regression refers to fixations that
are directed from right to left by "backwards" or regressive movements during reading
Return-sweep saccade
refers to the larger right to left saccade that shifts the eye from near the end of one line to near the beginning of the next line of text
VOR keeps the retinal image stable and clear, as motion of retinal images of ________ degrees/sex is enough to reduce VA
3-5
Translational Vestibulo-ocular Reflex has a latency of
35 msec

remember= VOR takes 16 msec and OKN takes 70 msec
VOR VOR system is unable to compensate for ______ frequency, _______ head rotations
low

sustained
The greter the phase shift, te sammer the
Time Constant
When the subject is rotated in darkness and they imagine a visual stimulus is moving together with their head, gain
decreases

This is probably due to the fact that if an object appears to be already tracked, there is no need to compensate with more eye movement
Visual suppression involes
a decrease in visualsensitivity so that the visual system becomes less efficient in detecting retinal image smear. This is a sensory mechnaism.
When a large patterned OKN drum is rotated about _________, the subject will develop a sensation of self rotation, which is known as _______-
60 deg/sec

circularvection
If the suject looks at the moving drum pattern attentiively, the eve velocity will be ______ then when the subject stares passively at the rotating surround
greater
Adaptation of VOR using reversed prisms causes the visual scene to move in the same direction as the turn. This causes the VOR's slow phase to
be in the same direction of the head turn. This is known as PLASTIC change, as VOR will return to normal after subject stops wearing prisms for awhile.
Optimal Velocity of VOR and OKN
High frequency, fast

Slow, low frequency movements
Nature of stimulus of VOR and OKN
head rotation/vestibular cues

Visual cues
Latency to respond of VOR and OKN
16 msec
70 msec
With sustained rotation, the cupula returns to tis restiing position with a time constant of about ____ , which is how long VOR would take if there was no velocity storage mechanism.
6 seconds
Head velocity value is derived by __________ integrating the angular head acceleration value sensed by the canals.

a. mechanically
or
b. electronically
mechanically
The eye position signal is generated from head velocity signal given by the semicircular anals. Where is the eye position signal being generated?
Medvial vestibular nucleus and nucleus prepsitus hypoglossi act as NEURAL integrators that conver eye velocity into eye position signal.
If we excite the LEFT vestibular nuclei and INHIBIT the right vestibular nuclei, which direction would we look?
We would look to the RIGHT

LEFT Vetibular nuclei excites IPSElateral 3rd nerve and CONTRA-lateral 6th nerve.
Righ Vestibular nuclei inhibits ispelateteral 3rd nerve and contralateral 6th nerve so you look Right
In higher ordered animals, the predominant processing of OKN occurs in the __________ and is routed through the middle temporal, superior temporal and posterior partieal before reaching the AOS
Cerebral cortex