Lecture 14 Objectives Flashcards
What are the three types of fixational eye movements?
Microtremor
Microsaccades
Microdrift
What is the amplitude of microtremors?
5-30 minutes of arc
Which is smaller, microsaccades or microtremors?
Microtremors
What is the frequency of microtremors?
50-100 Hz
What is the mean amplitude of microsaccades?
6 minutes of arc
T or F: The amplitude of microsaccades is usually less than 26 minutes of arc.
True
T or F: Microtremors are low frequency and high amplitude.
False - high frequency and low amplitude
What is the frequency of microsaccades?
120 Hz
What is the purpose of microdroft?
To prevent the image of a stable object from drifting off the retina
What is the velocity of microdrift?
less than 20 minutes of arc per second
Which of the fixational eye movement have no known function?
Microsaccades
What are the four types of fixation anomalies?
Anomalous slow drift
Saccadic intrusions
Saccadic oscillations
Nystagmus
What is the magnitude of anomalous slow drift?
1 degree or more
What is the most common cause of anomalous slow drift?
Amblyopia
Many conditions involving the ___ may cause anomalous slow drift.
Fovea
What is the definition of saccadic intrusions?
Sporadic, biphasic disruptions of fixation
The frequency of normal saccadic intrusions increases with ___.
Age
A normal saccadic intrusion shows a square wave jerk movement with an amplitude of what?
0.5-3 degrees
What is the amplitude of a macro-square wave jerk movement?
4-50 degrees
Saccadic intrusions are associated with what?
Cerebellar or brainstem diseases
What are saccadic oscillations?
Continuous disruptions of fixation
What are the two types of saccadic oscillations?
Macrosaccadic oscillation
Opsoclonus
What are macrosaccadic oscillations?
A series of large saccades that straddle fixation, but never fixate correctly
Patients with macrosaccadic oscillations can’t make which type of saccade?
Commanded (voluntary) saccade
