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236 Cards in this Set
- Front
- Back
5 major eye movements
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OKN
VOR pursuits saccades vergences |
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What deters retinal slip?
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VOR
OKN |
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What eye movements let you change the angle of gaze?
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pursuits
saccades vergences |
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What prevents fading of visual images?
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microsaccades
drifts tremors |
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When you feel as if the world is moving it is called
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oscillopsia
|
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What type of nystagmus do people tend to notice more visual problems: aquired or congenital?
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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 |
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When do VOR and OKN begin to develop?
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At birth
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At what age do saccades develop?
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At birth
|
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At what age do pursuits begin and develop?
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6-8 weeks
|
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At what age does vergences, accomodation, and binocular vision begin and develop?
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3 months
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What is the orbital plant?
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The "apparatus" within the orbit: tissue, EOMS, neurons, cortex, brainstem, etc
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Strabismus can occur due to what two things?
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muscular OR neural control
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What is viscous drag?
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The resistance that must be overcome to initally move the eye
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What is elastic restoring forces?
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Occurs when the eye is displaced, it is the force needed to be overcome in order to move eye to a new position
|
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Pulse signal
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the PHASIC increase in neural activity.
Allows the EOM to overcome VISCOUS drag |
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What overcomes viscous drag?
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Pulse/phasic signal --> burst of neural activity right before eye moves to give it the necessary push
|
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Step signal
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SUSTAINED increase in neural acitivty, allows EOM to work against the ELASTIC FORCES of the orbit tussue
|
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What overcomes the elastic forces of the eye?
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Step/sustained signal
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__________ firing leads to the movement of the eye followed by a ________ signal to the muscle in order to maintain the new position
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Pulse
Step |
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Without pulse, eye movement is _____
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slow
|
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Without step, eye position cannot be ____
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maintained
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Where is the problem located for internuclear opthalmoplegia?
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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 |
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What kind of problem is gaze- evoked nystagmus?
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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 |
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Is end point nystagmus abnormal or normal?
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normal
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Internuclear Ophthalmoplegia
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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 |
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SPINOCEREBELLAR ATAXIAS
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See nystagmus when gazing in either direction: right or left. And then see REBOUND when looking centrally
|
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Wernicke's Encephalopathy
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--> Lack of Vitamin B, seen in alcoholism.
See abnormal eye movements/nystagmus |
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T/F Eye movements can undergo adaptation changes
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True
When you get new glasses, you need to adapt your VOR due to magnification changes |
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What plays a large role in motor plasticity? And what parts are most involved?
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Cerebellum
Flocculus, nodulus, dorsal vermis |
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2 Prerequisites for eye movements?
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Orbital plant AND neural signals
|
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Afferent system for accurate eye movements provides info for?
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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) |
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2 sources of afferent system?
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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. |
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Efference copy is part of the ______ system
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afferent
|
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Efferent system for accurate eye movements provides info for?
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Tells the brain where and by how much to move the eye= how much PULSE and STEP signal to generate
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Ocular Motor nuclei involved in controlling EOM movements?
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3,4,6
|
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Oculomotor nuclei controls
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medial, superior, inferior rectus and inferior oblique.
It also controls levator, pupil size, accomodation and lacrimal gland |
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Abducens nuclei controls
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lateral rectus
|
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Trochlear nerve controls
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Superior oblique
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Twitch fibers
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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 |
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What are GLOBAL fibers?
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Twitch fibers, all or nothing action potential, pulse signals
|
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Non-twitch fibers
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Tonic/STEP receivers.
These have graded contrations, high oxidative capacity. Are known as ORBITAL fibers. These are good for maintaining new eye positions. |
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Wat are ORBITAL fibers?
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Non-twitch, graded, step signals
|
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What is the Center of rotation?
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NOT a fixed point inside the globe, but a locus of points known as the SPACE-CETROID OR BODY CENTRODE.
|
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Reason for why there is no center of rotation?
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Due to the fact that eye rotation is also accompanied by small TRANSLATIONAL movements.
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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) |
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Duction means
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rotation of ONE eye
|
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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 |
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True torsion
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Rotating around Fick's Y axis
|
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Equator definition
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circumfrence of eye that represents a locus of points equidistant from the ANTERIOR and POSTERIOR poles of the globe.
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Listing's plane defintion
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= 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) |
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Primary position
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look straight ahead into the distance
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Secondary position
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Look up-down AND right to left.
Rotation around Z or X axis |
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Tertiary position
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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 |
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Muscle plane
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2 lines joining the center of rotation at the MUSCLE axis.
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What wraps around the eye and anteriorly attaches to the wall of the orbit?
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Tenon's capsule, and the attachment to the wall is the CHECK ligament.
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Superior check ligament
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Whitnall
|
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Inferior check ligament
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Lockwood
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Nasal check ligament
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medial
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Temporal check ligament
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Temporal
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Check ligament defines _______
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the limit of eye rotation, affects the field of fixation
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Anatomical insertions
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physical point of insertion of EOM to the eyeball
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Physiological insertion
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point on the muscle that TANGENTIAL to the eye, where the torque of the muscle acts to rotate the globe.
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Arc of contact
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Angle created where the anatomical and physiological insertions points are connected to the center of rotation
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Action of medial rectus muscle in 3 positions
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adduction
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Actions of lateral rectus muscle in 3 positions
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abduction
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Actions of inferior rectus muscle in 3 positions
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depression, extorsion, adduction
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Actions of superior rectus muscle in 3 positions
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elevation, intorsion, adduction
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Actions of inferior oblique muscle in 3 positions
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extorsion, elevation, abduction
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actions of superior oblique muscle in 3 positions
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intorsion, depression, abduction
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Superior muscles ______
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INTORT
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Oblique muscles ________
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ABDUCT
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Inferior muscles _________
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EXTORT
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CARDINAL positions: H figures
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OD OS
SR IO IO SR LR MR MR LR IR SO SO IR |
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How to isolate SR muscle
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look out 23 degrees
|
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How to isolate SO muscle
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Look toward nose by 54 degrees
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Sherrington's Law of reciprocal innervation
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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 |
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Hering's law of equal innervation
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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 |
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Fick system of torsion
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horizontal movements followed by vertical eye movement= Rotation around the Z axis followed by the X axis
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Helmohltz system of torsion
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Vertical followed by Horizontal movements. Rotation around the X axis followed by rotation around the Z axis
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Donder's Law on rotation of tertiary position
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depends upon the horizontal and vertical gaze angles, IRRESPECTIVE of how eye reaches position. Requites TWO seperate movements
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Listing's Law on rotation of tertiary position
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Rotation about the Listing's plane. Movement on one axis causes the eye to move to that position in ONE single movement.
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Foveal fixation to a peripheral object is accomplished either:
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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) |
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Field of fixation=
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how much the eye can rotate with the object of interest still on the fovea
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T/F Monocular field of fixation is greater than binocular field of fixation
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True
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T/F The ability to rotate the eye changes drastically with age
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False
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The monocular field of fixation is roughly______ and the binocular field of fixation is roughly_______
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30-40 degrees
60-100 degrees? according to NTS |
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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 |
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Diagnostic field of action of eye movementsi s tested using:
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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 |
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When conducting ductions or versions, what would you expect a normal patient NOT to report?
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Double vision/diplopia, pain
|
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When conducting ductions or versions, what happens when the target excursion is too large?
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End point nystagmus or head movement
|
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When conducting ductions or versions, what do you look for?
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Underaction/restricted action and overaction of the EOMS
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If patient is looking to their nose you are testing which muscles?
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Obliques
|
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1. Abnormal small amplitude saccades suggest __________ disorder
2.Abnormal large amplitude saccades suggest ___________ or _____ disorders |
1. central neural
2. peripheral neural or EOM |
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The Supranuclear center of the brain gives the signal for:
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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" |
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Oculomotor nerve palsy lesion results in and occurs due to?
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dilated pupil, stabismus (up abd out eye), partial ptosis.
Can occur with pituitary tumor supressing CN 3 |
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Abducens Nerve Palsy results in
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problems abducting eye, possible esotropia.
|
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Trochlear Nerve Palsy results in
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SO disfunction
|
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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? |
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How does the visual system compensate for undesirable retinal image movement?
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VOR and OKN are compensatory eye movements
The INITIAL eye movement is VOR |
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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
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opposite
|
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The ____ phase eye rotation in VOR is the _____ direction to head roation to compensate for ead movment
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slow
opposite |
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the slow phase of VOR is in the SAME direction as ________
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"perceived motion"
|
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VOR is created when _________ are stimulated
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semicircular canals.
Thus, the INNER ear controls VOR. NOT visual imput |
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T/F VOR occurs even when eyes are closed
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True
|
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VOR is initated _____ msec after the semicircular canals are stimulated
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16 msec
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OKN is initiated ______ msecs after visual image motion
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70 msec
|
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OKN --> optokinetic nystagmus
Is induced by? |
bisual input
|
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Translational vestibular ocular reflex is induced by
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linear/translational head movments by stimulation of the otoliths (UTRICLE)
|
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Ocular counter rolling is induced by the stimulation of the
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otoliths (SACCULE) during static head tilt
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Cervico-ocular reflex is stimulated due to
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somatosensory stimulation (head and body movements)
|
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VOR Three Neuron Arc Circuitry
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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 |
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The slow phase of VOR is known as the ___________ movement and the fast phase is known as the _________ movement
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compensatory eye movement
saccadic eye movement (THIS IS NOT VOR) |
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Doll's Eye Testing tests
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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. |
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VOR occurs with _________ frequency head while OKN occurs with ______ frequency head rotations
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fast
slow |
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OKHN moves in the direction of the
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actual stimulus motion.
(moves in the same direction as VOR) |
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To produce VOR and OKN at the same time, test with
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lights on/eyes open, head rotation.
If its dark, only VOR will occur. |
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Post Rotational Nystagmus is
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the after effect of VOR
|
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Optokinetic after nystagmus is
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the after effect of the OKN
|
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What stops the residual eye movemnt at the termination of ration, thus preventing vertigo and dizziness from occuring?
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OKAN cancelling out the PRN
|
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The slow phase of PRN is the ___________ of the slow phase of VOR
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opposite
Therefore PRN is in the same direction of head rotation |
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OKAN is in the ________ direction of OKN
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same direction
Therefore OKAN occurs in the opposite direction of head rotation/ same direction as VOR |
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TVOR (Translational Vestibular Ocular Reflex)is tested using:
|
Head Heave response (tests translational movement)
Head Impulse test (tests rotation) |
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Which compensatory eye movement is NOT stimulated by the vestibular system?
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OKN --> visual
|
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Gain=
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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 |
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If Gain=1
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If =1, there is perfect compesation and output=input
|
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If Gain <1
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If <1, output is less then input and a SACCADIC eye movement occurs since VOR is not perfectly cpensating retinal slip
|
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Phase=
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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=
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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 |
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The CLINICAL equivalent of gain, phase, and time constant=
|
accuracy
speed smoothness |
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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.
|
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If gain is low then
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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. |
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Factors that effect VOR gain
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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 |
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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. |
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If angular acceleration is ___________ then no VOR is produced since semicircular canals aren't stimulated
|
0
velocity is constant |
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When subject feels a sensation of self rotation, it is known as
|
circularvection
|
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When responding to a moving stimulus, the visual system first generates _______ but then OKN takes over
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Pursuits.
You first follow the drum target until brain realizes the repetition of the spinning drum and OKN takes over. |
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OKAN is generated by__________ and helps to neutralive the ____
|
the velocity storage mechanism
PRN |
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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. |
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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
|
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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. |
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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
|
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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
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a problem within the semicircular canals or central projection of canals.
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Sensation of body tilt is a problem with
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the otolith system
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Testing vestibular function using: Static imbalance
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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. |
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Testing vestibular function using: Dynamic imbalance --> 2 manuvers used
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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. |
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Positionally induced imbalance --> dix-hallpike maneuver
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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 |
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Tullio phenomenon
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nystagmus whenever you hear a certain sound
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Caloric testing --> BOARDS loves it
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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 |
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Caloric testing in comatose patients
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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 |
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Jerk nystagmus
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well defined also and fast phase
usually found in amblyopia |
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Pendular nystagmus
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no defined fast phase
Can occur due to foveal disoders, or loss of fixation reflex. |
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Latent nystagmus manifests if you
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occlude the better seeing eye, due to reduced fixation.
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Null point=
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certain eye and head position which minizes nystagmus --> find it by doing versions. Then use prisms to shift the image to the null point
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For nystagmus treatment, use BASE OUT prism if
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convergence is found to reduce nystagmus
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For nystagmus treatment, use yoked prism if
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extreme head turn reduces nystagmus. Put the base towards the null point to reduce head turn
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T/F You put the BASE of the prism towards the null point to reduce head turn
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true
put base in the direction you turn your head |
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Problem: head turn to the right, eye turns to the left.
Solution: |
Solution: base right prisms reduce head turn to right
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Direct ophthalmoscopy/Visuoscopy
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Stability of fixation and to determine fixation is central or eccentric.
Do DO with spider web pattern. |
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Three criteria for constructing an eye tracking instrument
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index of measurement
a measurement device/detector amplifying device |
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Electro-oculography EOG
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index of measure: electric potential difference as the direction of gaze changes
Measurement device: electrodes Amplifier: computer |
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Infra-red tracking device:
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Index of measurement: IR reflected from iris and sclera
Measured using: IR photodetector, photcell in goggles that measure reflectance. Amplifier: computer good for peds |
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Purkinje image tracker
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index of measure: purkinje image OR reflected white light from cornea
measured using: static photographic or dynamic video amplifier: computer |
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Sclera contact lens optical level tracker
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BEST test for researchers!!!
index of measurement: light reflected off a mirror attached to CL measured using: video camera amplifier: computer |
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Sclera contact lens: magnetic search coil
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GOLD STANDARD FOR MEASURING EYE MOVEMENTS
index of measurement: change in electrical voltage. measuring device is a wire in CL amplifier: computer |
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GOLD STANDARD FOR MEASURING EYE MOVEMENTS
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Sclera contact lens: magnetic search coil
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the vestibulocerebellum (floccus and nodulus) controls
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pursuits and VOR
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THe dorsal vermise of the cerebellum controls
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saccades
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"for the sake of simplicity" the center of rotation of the eye is a fixed point that lies
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13.5 mm behind the corneal apex and 1.6 mm to the nasal side of the geometric center of the bloge
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Superior rectus makes an angle of _______ in primary position
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23-25
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Inferior rectus makes an angle of _______ in primary position
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23
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Superior Oblique makes an angle of _____________ in primary gaze
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51
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rotate OKN drum with stries oriented vertically, the fast and slow phases of OKN are?
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slow phase follows the stripes down
fast phase= eyes move back up |
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As you increase speed your OKN....
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increases, but at higher speeds, it begins to break down and VOR is stimulated
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After the subject experiences OKN for awhile, stop the drum rotation, is OKAN 1 present?
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It is present but it cannot be seen because presence of visual cues mask OKAN
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initate OKN on a subject with one eye occluded, experimenter looks behind occluder, is the occluded eye undergoing OKN as well?
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YES
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If you actively follow the rotating drum, is this a true OKNN?
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No, you follow the stripe using PURSUITS
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After spinning patient clockwise, we observe an eye movement, which one? What are the fast and slow phase direction?
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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. |
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Definition of practical field of fixation
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when fixation is achieved by both head and eye movements
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reflexive saccade
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generated to a novel stimli that unexpectedly occurs within the environment
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Volitional saccade
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can be predictive/anticipatory
can be generated on command can occur to move eyes to a remembered target (like a clock) |
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spontaneous saccades
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seemingly random saccades that occur when subject is not required to perform any specific task
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1. End point of convergence
2. End point of accomodation |
1. diplopia, eye turn
2. Blur, increase in pupil size |
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fixation during reading....
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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
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Regression refers to fixations that
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are directed from right to left by "backwards" or regressive movements during reading
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Return-sweep saccade
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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
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VOR keeps the retinal image stable and clear, as motion of retinal images of ________ degrees/sex is enough to reduce VA
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3-5
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Translational Vestibulo-ocular Reflex has a latency of
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35 msec
remember= VOR takes 16 msec and OKN takes 70 msec |
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VOR VOR system is unable to compensate for ______ frequency, _______ head rotations
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low
sustained |
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The greter the phase shift, te sammer the
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Time Constant
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When the subject is rotated in darkness and they imagine a visual stimulus is moving together with their head, gain
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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 |
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Visual suppression involes
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a decrease in visualsensitivity so that the visual system becomes less efficient in detecting retinal image smear. This is a sensory mechnaism.
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When a large patterned OKN drum is rotated about _________, the subject will develop a sensation of self rotation, which is known as _______-
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60 deg/sec
circularvection |
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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
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greater
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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
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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.
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Optimal Velocity of VOR and OKN
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High frequency, fast
Slow, low frequency movements |
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Nature of stimulus of VOR and OKN
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head rotation/vestibular cues
Visual cues |
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Latency to respond of VOR and OKN
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16 msec
70 msec |
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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.
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6 seconds
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Head velocity value is derived by __________ integrating the angular head acceleration value sensed by the canals.
a. mechanically or b. electronically |
mechanically
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The eye position signal is generated from head velocity signal given by the semicircular anals. Where is the eye position signal being generated?
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Medvial vestibular nucleus and nucleus prepsitus hypoglossi act as NEURAL integrators that conver eye velocity into eye position signal.
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If we excite the LEFT vestibular nuclei and INHIBIT the right vestibular nuclei, which direction would we look?
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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 |
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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
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Cerebral cortex
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