Lecture 12 Objectives Flashcards
What is the saccadic hierarchy from low to high?
Quick phases of VOR/OKN Visually guided (reflexive saccades) Volitional saccades (1-4) 1. to command 2. Predictive, anticipatory 3. Memory guided 4. Antisaccades
What are the five characteristics of saccades?
Latency Velocity Duration Amplitude Accuracy
What is normal latency of saccades?
200msec, +-50
What things affect latency?
Patient motivation
Attention
Target predictability
What is the normal velocity range for saccades?
30-700 degrees per second
What is the max speed of saccades?
1000 degrees per second
Peak velocity of saccades increases with what?
Amplitude
What is the normal duration of saccades?
30-100msec
Duration of saccades increases with what?
Amplitude
Which two characteristics of saccades demonstrate a main sequence relationship?
Velocity
Duration
What is the normal amplitude for saccades?
Less than 15 degrees
Gaze changes larger than 15 degrees usually stimulate what?
Head movement as well as saccadic eye movement
How is accuracy of saccades described?
Hypometria
Hypermetria
When does hypometria tend to occur?
With large amplitude saccades
When does hypermetria tend to occur?
With small amplitude saccades
Hypometria is usually less than __% of the overall amplitude.
10%
If there is a lesion in the fastigial nuclei, what type of saccades will most likely be seen?
Hypermetric saccades
With age, what happens to saccadic latency?
Increases by 1-2msec per year
With age, what happens to saccadic peak velocity?
Decreases by 1 degree per second, per year
With age, what happens to saccadic gain and accuracy?
They don’t change with age
What may reduce saccadic gain and accuracy?
Fatigue
What is the saccadic pulse?
A phasic muscle contraction that moves the eye rapidly against the orbital tissues
What is a saccadic step?
A tonic muscle contraction to hold the eye steady at its new position
What determines saccadic velocity?
Pulse innervation - the higher frequency of firing causes faster movement
