8. Ocular Motor Control
Part 4 of 5
Valentin Dragoi, Ph.D.
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Clinical Signs of Damage to Ocular Motor Systems (continued)
Symptoms. A 55 year-old male was brought to the emergency room. He was overweight and reportedly normally right-handed, a heavy smoker and drinker. He had lost consciousness during a game of basketball and when he awoke, appeared confused. When examined in the ER, he was conscious but followed no commands and could not repeat. He could mimic gestures and was able to voluntarily look to the left and right (Figure 8.9). His eyes followed a pen moving to his right with a smooth pursuit movement. However, his eye movements became jerky and ballistic at midpoint in the attempt to follow the pen as it moved to his left.
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You observe that the patient eyes
- tended to move about when at rest position
- have full mobility when performing saccades
- cannot smoothly track a visual target moving toward his left
You conclude that his functional loss
- is not sensory
- involves Wernieck's aphasia (i.e., impaired comprehension and inability to repeat)
- involves failure of smooth pursuit to the left
Side & Level of Damage: As his symptoms
- does not involve lower motor neurons or muscles
- involve upper motor neurons (i.e., conjugate lateral eye movements)
- involve cortical functions (i.e., aphasia)
you conclude that the damage involves the
- temporal-parietal cortex including Wernieck’s area
- left side (i.e., aphasia and no smooth pursuit to the left)
Neural imaging tests indicate infarction of branches of the left medial cerebral artery supplying the caudal superior temporal gyrus and inferior parietal gyrus.
Damage to the smooth pursuit circuit: Damage to the temporal eye field causes deficits in the ability to fixate on objects and to track them. Attempts to fixate on a target will be undermined by severe instability and wandering of the eyes. Tracking movements are jerky rather than smooth when attempting to follow an object moving in a direction toward (ipsilateral to) the side of the lesion. Note that the smooth pursuit circuit includes a double crossing and the temporal eye field controls ipsilateral eye movements (i.e., right cortex controls smooth pursuit to the right). When the temporal eye field is damaged, the two eyes may follow a visual target in an ipsilesional direction; but does so using the voluntary saccades circuit. That is, if the frontal cortical eye fields are intact, the eyes may be moved voluntarily (guided saccade) toward an object of interest ipsilateral to the impairment. However, in this case, the movements will be jerky unlike the eye movements in smooth pursuit. Tracking of visual targets contralateral to the lesion will be smooth.
SummaryThis chapter reviews the ways in which voluntary eye movements are initiated by cerebral cortical activity and involve more ocular motor control structures than the simple ocular reflexes. The cortical areas initiate eye movements and work through brainstem ocular motor centers to produce a response, i.e., there are no direct connections between the cerebral cortex and the extraocular motor nuclei. The smooth pursuit system utilizes a pontine nucleus, the cerebellum, and the vestibulo-ocular reflex pathway to execute eye movements to tract visual targets. The voluntary saccades system is similar to other voluntary motor systems in engaging areas in the frontal cortex to initiate the response and in influencing the motor neurons indirectly through lower motor control structures (i.e., the vertical and horizontal gaze centers). The gaze centers function to coordinate and control the activity of motor neurons to insure that the extraocular muscles act synergistically to produce conjugate saccades.
Test Your Knowledge
- Question 1
- A
- B
- C
- D
- E
The pontine paramedian reticular formation is involved in which of the following?
A. Vestibular nystagmus
B. Optokinetic nystagmus
C. Saccades
D. Smooth pursuit
E. Accommodation
The pontine paramedian reticular formation is involved in which of the following?
A. Vestibular nystagmus This answer is INCORRECT. Vestibular nystagmus is elicited by stimulation of the vestibular receptors and involves structures in the vestibulo-ocular response pathway.
B. Optokinetic nystagmus
C. Saccades
D. Smooth pursuit
E. Accommodation
The pontine paramedian reticular formation is involved in which of the following?
A. Vestibular nystagmus
B. Optokinetic nystagmus This answer is INCORRECT. These eye movements are elicited by slowly moving visual targets.
C. Saccades
D. Smooth pursuit
E. Accommodation
The pontine paramedian reticular formation is involved in which of the following?
A. Vestibular nystagmus
B. Optokinetic nystagmus
C. Saccades This answer is CORRECT! The frontal eye field neurons send control signals to the pontine paramedial reticular formation for voluntary horizontal eye movements (i.e., to direct the eyes toward an object of interest on or command to direct the gaze to the left or right).
D. Smooth pursuit
E. Accommodation
The pontine paramedian reticular formation is involved in which of the following?
A. Vestibular nystagmus
B. Optokinetic nystagmus
C. Saccades
D. Smooth pursuit This answer is INCORRECT. The pontine paramedial reticular formation is not part of the smooth pursuit pathway, which involves the dorsal pontine nuclei, cerebellum and structures in the vestibulo-ocular pathway.
E. Accommodation
The pontine paramedian reticular formation is involved in which of the following?
A. Vestibular nystagmus
B. Optokinetic nystagmus
C. Saccades
D. Smooth pursuit
E. Accommodation This answer is INCORRECT. The pontine paramedial reticular formation is not part of the accommodation neural circuitry. For example, it is not involved in the convergence of the two eyes.
- Question 2
- A
- B
- C
- D
- E
A 57-year old male with a past history of high blood pressure awakens with a terrible headache. His eyes tend to drift about and when he is asked to track a pen moving to his left, both eyes move in short, jerky steps. In contrast, both eyes move smoothly when his eyes track a pen moving to his right. Given the patient's history, a radiological study is scheduled to determine whether a stroke had occurred. The study determines the area of infarction to include which of the following?
A. Left abducens nerve
B. Left medial longitudinal fasciculus
C. Right frontal lobe
D. Right temporal lobe
E. Left temporal lobe
A 57-year old male with a past history of high blood pressure awakens with a terrible headache. His eyes tend to drift about and when he is asked to track a pen moving to his left, both eyes move in short, jerky steps. In contrast, both eyes move smoothly when his eyes track a pen moving to his right. Given the patient's history, a radiological study is scheduled to determine whether a stroke had occurred. The study determines the area of infarction to include which of the following?
A. Left abducens nerve This answer is INCORRECT. If it were damaged, the left eye could not be moved to the left - even in jerky movements.
B. Left medial longitudinal fasciculus
C. Right frontal lobe
D. Right temporal lobe
E. Left temporal lobe
A 57-year old male with a past history of high blood pressure awakens with a terrible headache. His eyes tend to drift about and when he is asked to track a pen moving to his left, both eyes move in short, jerky steps. In contrast, both eyes move smoothly when his eyes track a pen moving to his right. Given the patient's history, a radiological study is scheduled to determine whether a stroke had occurred. The study determines the area of infarction to include which of the following?
A. Left abducens nerve
B. Left medial longitudinal fasciculus This answer is INCORRECT. If it had been damaged, the left eye would not have moved to the right while attempting to track an object moving to the right.
C. Right frontal lobe
D. Right temporal lobe
E. Left temporal lobe
A 57-year old male with a past history of high blood pressure awakens with a terrible headache. His eyes tend to drift about and when he is asked to track a pen moving to his left, both eyes move in short, jerky steps. In contrast, both eyes move smoothly when his eyes track a pen moving to his right. Given the patient's history, a radiological study is scheduled to determine whether a stroke had occurred. The study determines the area of infarction to include which of the following?
A. Left abducens nerve
B. Left medial longitudinal fasciculus
C. Right frontal lobe This answer is INCORRECT. If it were damaged, it would not interfere with smooth pursuit as it controls saccades toward the left.
D. Right temporal lobe
E. Left temporal lobe
A 57-year old male with a past history of high blood pressure awakens with a terrible headache. His eyes tend to drift about and when he is asked to track a pen moving to his left, both eyes move in short, jerky steps. In contrast, both eyes move smoothly when his eyes track a pen moving to his right. Given the patient's history, a radiological study is scheduled to determine whether a stroke had occurred. The study determines the area of infarction to include which of the following?
A. Left abducens nerve
B. Left medial longitudinal fasciculus
C. Right frontal lobe
D. Right temporal lobe This answer is INCORRECT. The right temporal lobe contains neurons that control smooth pursuit toward the right.
E. Left temporal lobe
A 57-year old male with a past history of high blood pressure awakens with a terrible headache. His eyes tend to drift about and when he is asked to track a pen moving to his left, both eyes move in short, jerky steps. In contrast, both eyes move smoothly when his eyes track a pen moving to his right. Given the patient's history, a radiological study is scheduled to determine whether a stroke had occurred. The study determines the area of infarction to include which of the following?
A. Left abducens nerve
B. Left medial longitudinal fasciculus
C. Right frontal lobe
D. Right temporal lobe
E. Left temporal lobe This answer is CORRECT! Neurons in the left temporal lobe (middle superior and middle temporal gyri) are involved in detecting movement of objects in space and in guiding tracking eye movements during smooth pursuit. The left tracking movement is jerky because the frontal eye field is being used to guide the eye movement in saccades. The two eyes move to the left and if the object isn't in view, the eyes make another saccade to direct them towards the expected position of the moving object.
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