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. 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.
Notice at the "look straight" command, the patient's eyes tend to wander when at rest. Also notice at the "look left" command, the patient's eyes tend to move in a jerky, step-like manner. 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.
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.
This 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.
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.
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. Vestibular nystagmus is elicited by stimulation of the vestibular receptors and involves structures in the vestibulo-ocular response pathway. The frontal eye field neurons send control signals to the pontine paramedial reticular formation for voluntary horizontal eye movements i. 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.
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. A 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?
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. If it were damaged, it would not interfere with smooth pursuit as it controls saccades toward the left.
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. This section is included for those who wish to use further "clinical cases" to test their knowledge of ocular motor functions.
A patient visits his primary care physician at the urging of his wife. She noticed that his left eye lid was drooping slightly and that his face appeared flushed.
She was concerned he might have suffered a stroke. On examination, it was noted that his left pupil was much smaller than his right Figure 8.
Physical examination determines that touch, vibration, position and pain sensations are normal over the entire the body and face. There are no other motor symptoms. A1 Observe the patient's eyes under low illumination. Also observe the reaction of the patient's eyes to light directed in the left or right eye. Pathway s affected: You conclude that structures in the following motor pathway have been affected is. Sympathetic Innervation of the Eye.
Horner's syndrome is a constellation of symptoms that includes miosis, pseudoptosis and enopthalmosis sunken eyeball. It is characteristic of damage to the sympathetic innervation of the face provided by the superior cervical ganglion.
This syndrome also occurs when the hypothalamic output to the sympathetic preganglionic neurons in the lateral horn at T1 to T3 is interrupted or when the T1 to T3 anterior roots are damaged. A 35 year-old female complains that she has double vision when she attempts to look to the right. When looking straight ahead, both her eyes assume normal positions Figure 8.
She is able to look up and down and to the left with both eyes. However, she cannot adduct her left eye i. Both her eyes converge when a visual target is brought close to her eyes. Her vision and pupillary reflexes are normal in both eyes. She has normal sensation on her face and body and no other motor symptoms. A2 Observe the patient's response to the commands of the control buttons. Neural imaging tests indicate demyelination of the medial longitudinal fasciculus on the left side.
Damage to the medial longitudinal fasciculus. The medial longitudinal fasciculus MLF is a fiber tract that contains, in part, axons of the vestibular nuclei and of the contralateral abducens interneurons. Lesions in the MLF results in an abnormality of conjugate horizontal eye movements called an internuclear ophthalmoplegia. The medial rectus ipsilateral to the damaged MLF does not function during a lateral gaze in a contralesional direction.
If the damage is unilateral, both eyes can be moved in an ipsilesional direction during an attempted lateral gaze i. In contrast, the ipsilesional eye i. A3 The left medial longitudinal fasciculus has been damaged and cannot carry excitatory signals from the right abducens interneurons to the left oculomotor neurons controlling the left medial rectus. Recall the left MLF carries the axons of the right abducens interneurons to the left oculomotor neurons, which control the medial rectus of the left eye Figure 8.
Also recall that contraction of the medial rectus of the left eye directs the left eye nasally i. Both eyes are adducted on convergence as the axons from the supraoculomotor area to the oculomotor neurons controlling the medial rectus muscles of the two eyes are not affected by MLF lesions. Oblique, Sup. Lateral Pursuit: Medial Vestibular nucleus. Vertical Pursuit: Superior Vestibular Nucleus. Vestibular nystagmus B. Optokinetic nystagmus C.
Saccades D. It is controlled by the fourth cranial nerve trochlear nerve. A small pulley structure in the eye called the trochlea connects the superior oblique muscle from the sphenoid bone to the top of the eye, near the nose.
When the eye is in the primary position usually facing straight ahead , the main function of the superior oblique muscle is intorsion. It also moves the line of sight of the eye downward and outward. The inferior oblique eye muscle originates from the front of the orbital floor, close to the nose. It also elevates and abducts the eye moves the direction of gaze upward and outward.
Action of the inferior oblique muscle is controlled by the third cranial nerve oculomotor nerve. In addition to the six main extraocular muscles, the eye has another extrinsic muscle called the levator palpebrae superioris.
This muscle is the single muscle responsible for elevating the upper eyelid and keeping it in position. Its movement is controlled by the oculomotor nerve. While extrinsic extraocular muscles control the movement of the eyes, the function of intrinsic eye muscles is to focus the eye, and control the iris to allow a specific amount of light to enter it.
Of these muscle groups, the extrinsic muscles are the muscles around the eye and the intrinsic muscles are located in the eye. Extrinsic muscles are also voluntary, while intrinsic muscles are involuntary. The intrinsic eye muscles include the ciliary muscle, iris sphincter and radial pupil dilator muscles. If one of the extraocular muscles is too strong, too weak, or otherwise dysfunctional, an eye movement disorder can develop.
Eye movement disorders can be mild or severe. The main function of this muscle is to pull the pupil away from the midline of the body. The annulus of Zinn is a tendinous ring that surrounds the optic nerve and serves as the origin for four of the six extraocular muscles, excluding the inferior oblique muscle and superior oblique muscle.
The only function of the medial rectus is to bring the pupil closer to the midline of the body. This muscle shares an origin with several other extrinsic eye muscles, the anulus tendineus, or common tendon. It is the largest of the extraocular muscles and its only action is adduction of the eyeball. The inferior rectus is also a muscle of the orbit. This muscle has multiple functions, mainly helping to extort the eye. Here are more details of the inferior rectus muscle:. The inferior rectus muscle is the only muscle that is capable of depressing the pupil when it is in a fully abducted position.
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