Flashcards
Section IV Eye Movements review
Cards in this deck (55)
- 1In humans, the retina develops a ____ spatial resolution in the centre and a ____ spatial resolution in the periphery. What is this termed?high; . Foveal compromise
- 2Which type of eye movements shift the gaze to put the image onto the fovea (3)?1. Saccades
2. Pursuit
3. Vergence - 3Which type of eye movements keep gaze stabilized so the image will stay on the fovea?1. Fixation
2. Vestibular (VOR)
3. Optokinetic (OKN) - 4What is the purpose of eye movement?Eye movement is to move an image onto the fovea and to maintain it there during fixation
- 5Describe how the 3 eye movements bring an image onto the fovea?Saccades: bring the image of an object of interest rapidly onto the fovea
Smooth pursuits: Holds the image of a small moving target on the fovea
Vergence: Moves the eyes in an opposite direction (i.e. convergence or divergence) so that images of a single object are held simultaneously on both fovea - 6Describe how the 3 eye movements hold images steady the fovea?Fixation: holds the image of a stationary object on the fovea when the head is stationary
Vestibular (VOR): holds image steady on the retina during brief head movements
Optokinetic (OKN): Holds image steady on the retina during VF movements - 7Name and describe the 6 types of eye movements1. Fixation: Holds the image of a stationary object on the fovea when the head is stationary
2. Vestibular (VOR): holds the image steady on the retina during sustained head movements
3. optokinetic (OKN): holds image steady during VF or sustained head movements
4. Saccades: Bring the image of an object of interest rapidly on the fovea
5. Smooth pursuit: holds the image of a small moving target on the fovea
6. Vergence: moves the eyes in an opposite direction (convergence or divergence) so that the images of a single object are held simultaneously on both fovea - 8What are the two ways that the eye's movements can be categorized/described?Fast eye movements: 300 - 700 degress per second. These include the quick phase of nystagmus and saccades
Slow eye movements: 20 - 50 degrees per second. These include smooth pursuit, nystagmus slow phase, vestibular, and vergence movements - 9What does the term "latency" refer to? What factors does it depend on?The time between the stimulus and when the movement of the eye begins.
Depends on subject interest, lighting, movement of the object, medications, fixation, etc. - 10Describe pulse and step.Pulse: The increase in innervation that signals a movement
Step: the new tonus (constant low level acitvity) of the muscle that holds it in position - 11What is required to maintain the step phase?Neural integration is required to maintain the step phase (combines proprioception signals from the ocular motor neurons with input signals about eye velocity to tell how far the eye has moved and to keep the eye in that position)
- 12Eye movements can be thought of as which two systems working together?1. The neural signal for movement (pulse)
2. The muscular and orbital anatomy that execute the movement (slide and step) - 13Describe the three diagrams on this photoThe top diagram depicts the physical position of the globe. The beginning of the line shows the original eye position, and the stable line at the top shows where it holds the new position. The slide in between is the transition between positions which has both anatomic and neural significance.
The second line of the diagram denotes innervation and tonus. It shows the eye at baseline, the sharp climb as appropriate innervation is delivered, and the drop off as the burst fades away.
If we put these together, we get the third graph – saccadic eye movement!! - 14Describe what a saccade eye movement and a smooth pursuit eye movement look like on a graph
- 15What does eye movement use to minmize errors? What are the two different types?Feedback is used by the visual system as an improvement on the accuracy of movement.
Closed (required to maintain fixation) and open (somethin gin periphery catched your attention) feedback loops - 16What are the two types of stimluation that can lead to eye movements?Visual and non-visual stimulation
- 17What types of visual stimulation generate eye movements?Voluntary: includes command movements and all intentional movements
Association stimulus: Ex. looking toward a noise or a sudden visual stimulus. Both mediated through thr brainstem or association areas in the cortex and are reflex saccades. Can aslo be a non-visual stimulus if looking to where an object was "remembered" to be
Optokinetic stimulus: Image flow across the retina due to head or object movement
Blur or diplopia: Part of the near stimuls to produce convergence . Controlled by convergence cenre near CN III nucleus - 18What types of non-visual stimulation generate eye movements?Vestibular stimulus: stimulation of CN VIII causes conjugate movement of the eyes. Each movements of the head causes counter-rotation of the eyes. Dolls head maneuver is commonly used to produce this oculocephalic reflex
Association: Looking to where an object was "remembered" to be
Optokinetic Nystagmus (image movement) - 19What is the function of saccades?To bring the image of an object of interest rapidly onto the fovea
- 20What can all eye movements be described by?velocity (degrees/second), amplitude (how large of a movement), trajectory (a line in the direction of movement), and latency (period between stimulus and movement)
- 21How are velocity and amplitude of eye movements related?The bigger the movement, the faster the velocity
- 22What is latency dependent on? Why?Latency is dependent on the nature of the stimulus (the modality and the temporal properties of the target presentation). This is because latency reflects various aspect of visual procession, targert selection, and motor programming
- 23What are the only type of eye movements? Where in the brain are they generated?Saccadic eye movements. Are initiated by signals from the contralateral frontal cortex.
- 24What are saccadic eye movments? How fast are they? During which types of eye movements do they occur? How do the EOM coordinate to make saccadic movments? Deescribe vision during a saccadeSaccades are high velocity eye movements. Their velocity ranges from 300 - 700 degrees per second.
They occur during voluntary conjugate gaze and reflex changes in ocular fixation. Both eyes move in the same direction.
Saccades are produced by maximal contraction of the primary agonist and inhibition of the antagonist. Visual function (acuity and light) is suppressed during saccadic activity - 25What type of an eye movement is the fast phase of nystagmus?a saccade
- 26Describe the velocity, trajectory, latency, and ampitude of a saccadeV: 300 - 700 degrees per second
T: should look the same regardless of direction. If there is an impairment of horizontal or vertical movements, the trajectory looks curved
L: 200 ms
A: depends on velocity and target? - 27What is an anti-saccade?the patient is asked to make a voluntary saccade AWAY from the target
- 28What are the different types of saccades (5)?Volitional - predictive/anticipatory; memory-guided, antisaccades, to command
Reflexive - to novel stimuli that appear unexpectedly (visual, auditory, tactile)
Expressive - generated when a novel stimulus is presented after the fixation stimulus has disappeared
Spontaneous - random when a behavioural task is not required
quick phase of OKN (and nystagmus) - 29What are the four types of slow eye movments?pursuits, vergences, vestibular movements, OKN
- 30What are pursuits? How fast are they? Where are they generated in the brain? During which types of eye movements do they occur? How do pursuit movements remain accurate? Describe vision during a smooth pursuit.An involuntary slow eye movement that holds the image of a small moving target on the fovea.
Generated in the ipsilateral parieto-occiptal cortex
Occur involuntarily in when tracking a small moving stimulus
Remain accurate through closed feedback loops.
During pursuit, we suppress information provided by retinal slip (whole VF motion) and head movement (VOR and OKN are suppressed), as this would cause unwanted eye movements - 31What factors play roles in initiating and maintaining pursuit movements?illumination. size, location, background contours ,prediction, learning
- 32What is an interesting fact about pursuit movements?Pursuits can be trained to improve accuracy
- 33What are the stimuli/conditions for pursuit (4)?- Target velocity (retinal appreciation of motion)
- Position of the target (a position error)
- Proprioception (afferent input) e.g. tracking one’s outstretched finger in the dark; also uses knowledge of motor command to the limb
- Perception of motion (integration of retinal info with higher processing) - 34What are the three functions of smooth pursuit eye movements?1. Stabilizes the image of a small moving target on the fovea
2. Cancels the VOR during combined eye-head tracking
3. Cancels optokinetic nystagmus during tracking of a small, moving target against a
detailed stationary background. For example, during smooth tracking of a bird - 35Accurate fixation of the object of regard at any depth in the visual field requires the use of ________.vergence
- 36What is the only movement system that moves the eyes in opposite directions?The vergence system
- 37What are vergences? How fast are they? Where are they generated in the brain? During which types of eye movements do they occur? How are amplitude and trajectory determined? What is always required for a vergence movement?Vergences are disconjugate eye movements (convergence and divergence) that help maintain bifoveal fixation of an object at different distances.
Slow eye movements - 4-25 dg/s
The brain area for vergences is not well understood.
Occur during convergence, divergence, and some vertical movements as well (or torsional).
Amplitude and trajectory are determined by the new fixation point (by the location of the object)
Accurate fixation of the object of regard - 38Vestibular eye movements are due to signals originating in the ________.Inner ear
- 39What are the two most important stimuli for vergence movements?Retinal image blur and retinal disparity.
If the retinal image of an object is blurred, the target is either too near or
too far away. This results in a change in accommodation, which is accompanied by a change in pupillary size, as well as a change in vergence. Similarly, if a single object casts its image on noncorresponding points on the two retinas, vergence eye
movements are elicited to realign the lines of sight to achieve single binocular vision. - 40Along which meridian are vergences most robust? Why?Vergences are more robust against the horizontal meridian, because the eyes are separated horizontally in the head (vergences along this meridian are most useful)
- 41When an object is at optical infinity, the visual ines of sight are _____parallel
- 42What common disorder is found when there is a malfunction of vergence?Convergence insufficiency syndrome (among many other disorders): diplopia at near distances
- 43An abnormal relationship between ____ and ____ is a common cause of childhood strabismusvergence; accommodation
- 44What type of vergence does retinal blur elicit? Retinal disparity?Blur = Accommodative vergence
Retinal disparity = fusional vergence - 45What are vestibular eye movements? How fast are they? Where are they generated in the brain? Which direction? When do these movements start/stop?Vestibular eye movements are slow movements that stabilize gaze during movements of the head and body. Ex. Turning head left, eyes move right to maintain fixation. Occur with specific signals originating in inner ear.
Movements start wth head rotation and stop when head stops moving (visual input is NOT required) - 46What is optokinetic nystagmus? What types of eye movements happen? How can you stimulate OKN?Optokinetic nystagmus is a visually mediated reflex consisting of
smooth pursuit alternating with saccadic refixation as a series of objects cross the visual field. The eyes follow a moving object with smooth pursuit, then use a saccadic movement in the opposite direction to refixate on the next approaching target.
t. The
stimulus most commonly used to produce OKN is a pattern of
black and white stripes presented on a rotating drum or moving tape - 47Why might high prescription glasses cause some patients to become dizzy or nauseous?Due to a mismatch between head and eye velocity. High-powered glasses can minify or magnify the image on the retina, causing the image to be percieved as slower or faster than the neural integrator normally anticipates, with respect to head movement. This can cause dizziness or nausea until the system adjusts
- 48What is the function of fixation?To hold the image of a stationary object on the fovea when the head is stationary
- 49Is fixation a passive or active motion?Active. During fixation on stationary targets in primary position, there are miniature horizontal, vertical, and torsoinal drifts followed by microsaccades (error correction), accompanied by a high frequency tremor.
The movements around fixation may function to try and control the "noise" of the constant tonus of the muscles
- these may also be to moe the image off of certain retinal points to prevent bleaching - 50What is Bell's phenomenon? How can you observe it? What is the neural substrate for this movement?The upward and outward protective, reflexive, movement that rolls the corneas away from primary position when the lids are closed.
Can observe the phenomenon when you try to open tightly close eyelids.
Neural substrate is unknown, but though to be controlled by 7th and 3rd nerves (control cornea and lid) - 51Why is Bell's phenomenon an important reflex?To differentiate a movement pathway problem (e.g. supranuclear) from a mechanical muscle problem (restrictive).
If the Bell's phenomenon is intact, the inability to look up cannot be mechanical, it must be neurologic - 52How do illumination, size, location and background contours affect smooth pursuit? What about age, attentiveness, and medications?Pursuits may be slowed or inaccurate due to dim illumination, small size, distant proximiy, and interference from the environment
Increasing age, decreasing attention and stimulant/depressant medications will also slow pursuits - 53How do luminance, size, contrast, complexity of contours, location and timing of presentation of a new target affect saccades?Easier to see targets will produce faster and more accurate saccades.
Saccadic latency can be shortened if the current stimulus is shut off for a brief period before a new target is introduced - 54How do stimulus characteristics, location of the stimulus and type of disparity affect vergence movements?Targets that are easier to see and within easy visual range will increase the speed and accuracy of . Humans are faster at making convergent movement than divergent.
- 55What are the three distinct types of physiological miniature movements that are not detectable by the naked eye, during fixation?microsaccades, microdrift, and microtremor
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- 1º ano Orthoptics review - Year 1 (Module 2) Flashcards on Section IV Eye Movements review, created by Suh Dude on 03/11/2021.
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