Anatomy of Eye Movement for Assessment

In this video, we will go over the basic anatomy related to the clinical assessment of eye movements. Since we will not address visual acuity, visual field testing, visual reflexes, or autonomic innervation to the eye, we will concern ourselves only with the innervation and functions of the six striated extraocular muscles responsible for positioning the eyeball. Inferior rectus, lateral rectus, inferior oblique, superior rectus, medial rectus, and superior oblique. Each of these muscles receives motor innervation, general somatic efferent, from one of the following three cranial nerves. Oculomotor nerve, or cranial nerve 3, trochlear nerve, or cranial nerve 4, or abducens nerve, or cranial nerve 6. A convenient way to remember this pattern of innervation is provided by the formula LR6, SO4, R3. That is, lateral rectus muscle is innervated by cranial nerve 6, superior oblique muscle is innervated by cranial nerve 4, and the remaining muscles are all innervated by cranial nerve 3. Before discussing specifics of eye movements, we need to understand the relative position of the eyeball within the bony orbit of the skull. When the eye is in its primary position, looking straight ahead, the eye is in its primary position, looking The visual axis, represented by a line from front to back through the center of the eye, is parallel to the sagittal axis of the body. In this position, the eye deviates approximately 23 degrees nasally from the long axis of the bony orbit. In other words, in its primary position, the eye is significantly adducted. This will become important when we start assessing individual muscle movements in just a few moments, because all four of the recti... rectus extraocular muscles are aligned with the long axis of the bony orbit and, as we will see, relative amounts of adduction or abduction of the eyeball can alter some of their functions. We're almost ready to start assigning specific movements to the individual extraocular muscles, but first there is one final relationship to establish that will help us to visualize muscle functions. The distal insertions of all four of the rectus muscles are anterior to the horizontal axis of the eyeball. In contrast, the two oblique muscles have distal insertions posterior to the same axis. Understanding these insertions will greatly help in making sense of the muscles'functions. Now let us consider the six basic movements that the eyeball is capable of. Elevation, or looking up. Depression, or looking down. Adduction, looking in. Abduction, or looking out. Intorsion. rolling the top of the eye medially towards the nose, and extortion, rolling the top of the eye laterally away from the nose. Of course, these movements can and do occur in various combinations, some of which you will specifically assess during a routine examination of eye movements. For example, asking the patient to look up and out or down and in. The first four of the basic eye movements are relatively intuitive and easy to understand. The last two, intorsion and extorsion, are a little bit trickier and may or may not be assessed in a basic eye examination. Nevertheless, it's important to understand what these terms mean and why they are necessary for proper eye positioning. The rotational movements of intorsion and extorsion are necessary to keep a viewed object stable and positioned on the appropriate part of the retina as the head is tilted from side to side. To illustrate, Imagine standing upright and looking at an arrow that is pointing superiorly. Now tilt your head 45 degrees to the right. Does the arrow move with your head and now point at a 45 degree angle? Hopefully not. Because of intorsion and extorsion, the arrow should still appear to be pointing superiorly. In this case, the right eye has been intorted and the left eye has been equivalently extorted so that the image falls on the same part of the retina. as before the head tilt. Obviously, our eyes have a limited range of intorsion-extorsion. They cannot spin completely around within the orbit. And if we were to stand on our head, the arrow would appear to change direction and appear to point inferiorly. Now let's look at the movements produced by each one of the extraocular muscles. We'll start with the medial and lateral rectus muscles, since they are each responsible for producing a single, straightforward eye movement. Contraction of medial rectus causes adduction of the eye. Medial rectus is the primary adductor, though other extraocular muscles can assist in this movement. Contraction of lateral rectus causes abduction of the eye. Lateral rectus is the primary abductor, though again, other extraocular muscles can assist in this movement. The remaining four extraocular muscles are a little bit more complex, since they are capable of producing multiple eye movements, and their primary function changes depending upon the relative position of the eye within the orbit. The primary result of contraction of superior rectus is elevation of the eye. is most effective at elevating the abducted eye. With increasing adduction of the eye, superior rectus loses the mechanical advantage necessary for producing elevation, such that the fully adducted eye can be elevated only by the action of the inferior oblique muscle. In addition to its primary function, as an elevator of the eye, superior rectus also produces limited adduction and intorsion of the eye. The primary result of contraction of inferior rectus is depression of the eye. However, as is the case with superior rectus, the inferior rectus is most effective at depressing the abducted eye and loses the mechanical advantage necessary for depression as the eye is progressively adducted. The fully adducted eye can be depressed only by the superior oblique muscle. In addition to its primary function as a depressor of the eye, inferior rectus also produces adduction, and extortion of the eye. The primary result of contraction of inferior oblique is extortion of the eye. As mentioned earlier, inferior oblique also assists in elevation of the eye and is the only effective elevator of the fully adducted eye. Inferior oblique also contributes to abduction of the eye. Finally, let's consider the most misunderstood of the extraocular muscles. The primary result of contraction of superior oblique is intorsion of the eye. Superior oblique also assists with depression of the eye and is the only effective depressor of the fully adducted eye. Superior oblique also contributes to abduction of the eye. Superior oblique is often referred to as the down and out muscle because if acting in isolation, that is, With all or most of the other muscles inactive, such as occurs with third nerve palsy, or a quote, blown third nerve, it does put the eye in the down and out position. However, as we will see, the function of superior oblique is not tested by having the patient look in the down and out direction, but rather in the down and in direction. This is because the coordinated function of other muscles, specifically lateral rectus and inferior rectus, can put the eye in the down and out position, but only superior oblique is able to depress the fully adducted eye, that is, to put the eye in the down and in position. This discrepancy between the pure, isolated function of superior oblique and the clinical test of superior oblique function often causes confusion for students and clinicians alike. Now we're ready to understand the basic eye movement exam that tests the function of each extraocular muscle by having the patient sequentially look in each of six cardinal directions, also referred to as the six cardinal fields of gaze. These are in, up and in, down and in, out, up and out, and finally down and out. The basic exam involves having the patient focus on an object. that is positioned 18 to 24 inches in front of their face as you move the object through a large H shape to encompass the six cardinal fields of gaze. The eyes can be examined individually or together. In our example both eyes will be tested at the same time. Begin by allowing the patient to focus on the object with both eyes in the primary position, that is looking straight ahead, neither elevated nor depressed. Slowly move the object to the patient's left until you reach the limit of his field of view. Here the patient's left eye should be fully abducted and the right eye should be fully adducted. This position tests the function of the left lateral rectus muscle and the right medial rectus muscle. Now move the object directly superiorly. This position tests the patient's left superior rectus muscle, up and out, and the right inferior oblique muscle, up and in. Continue by moving the object directly inferiorly to test the patient's left inferior rectus, down and out, and the right superior oblique muscle, down and in. Now return the object to the left horizontal position and slowly move it to an equivalent position on the right side. Here you can examine the function of the patient's right lateral rectus muscle, abduction, and the left medial rectus muscle, adduction. Again, raise the object directly superiorly to test the right superior rectus muscle, up and out, and the left inferior oblique muscle, up and in. Move the object directly inferiorly to complete the exam by testing the right inferior rectus, down and out, and the left superior oblique muscle. down and in. You have now tested the six cardinal fields of gaze for each eye. There are other things that can be assessed with this basic eye exam, including smooth pursuit and the presence or absence of nystagmus. However, these are beyond the scope of this video. While this exam involves direct assessment of individual muscle movements, it is also an efficient functional test for the three cranial nerves that innervate the extraocular muscles. And in fact, disturbed eye movements result more often than not from central or peripheral nerve disorders rather than from mechanical causes such as muscle entrapment or trauma. Let's briefly go over what to expect with complete disruption of these cranial nerves. For the sake of simplicity, we will assume damage to the brainstem motor nucleus of each nerve rather than a more distal lesion is the cause of the deficit. Complete disruption of oculomotor nerve function or third nerve palsy, results in paralysis of four extraocular muscles, superior rectus, inferior rectus, medial rectus, and inferior oblique. Patients with this disorder present with the ipsilateral eye stuck in the down and out position due to the fact that tonic activity of the intact lateral rectus muscle fully abducts the eye because it is no longer opposed by the medial rectus muscle. Further, the eye is depressed. because the action of superior oblique is no longer opposed by the elevation normally provided to the abducted eye by the superior rectus muscle. Because lateral rectus and superior oblique are the only remaining functional muscles, the eye is unable to move from this position. Complete disruption of the trochlear nerve function, or fourth nerve palsy, results in paralysis of the contralateral superior oblique muscle. The trochlear nerve is the only motor cranial nerve that decussates or crosses to the other side. Patients with this disorder are unable to depress the affected eye when it is adducted or in the primary position due to the fact that the intact inferior rectus loses the ability to depress the eye as it is increasingly adducted. In addition, these patients are unable efficiently to intort the affected eye. Both of these lost functions can result in, quote, double vision. Many patients unconsciously compensate by tucking the chin, which eliminates the need to depress the affected eye, and tilting the head away from the affected eye, which eliminates the need to intort the affected eye. An eye movement exam of patients with trochlear nerve palsy reveals an inability to put the affected eye in the down and in position. Finally, complete disruption of abducens nerve function, or sixth nerve palsy, causes paralysis of the ipsilateral lateral rectus muscle and an inability to fully abduct the affected eye. These patients typically experience double vision, except during near vision when both eyes are directed inward. Eye movement exam reveals an inability to abduct the affected eye beyond the primary position. Some of these patients compensate by turning their head toward the injured side, which allows them to adduct the affected eye and pair it with the normal eye, which will be abducted to a corresponding degree.

Each of these muscles receives motor innervation, general somatic efferent, from one of the following three cranial nerves. Oculomotor nerve, or cranial nerve 3, trochlear nerve, or cranial nerve 4, or abducens nerve, or cranial nerve 6. A convenient way to remember this pattern of innervation is provided by the formula LR6, SO4, R3. That is, lateral rectus muscle is innervated by cranial nerve 6, superior oblique muscle is innervated by cranial nerve 4, and the remaining muscles are all innervated by cranial nerve 3. Before discussing specifics of eye movements, we need to understand the relative position of the eyeball within the bony orbit of the skull. When the eye is in its primary position, looking straight ahead, the eye is in its primary position, looking The visual axis, represented by a line from front to back through the center of the eye, is parallel to the sagittal axis of the body. In this position, the eye deviates approximately 23 degrees nasally from the long axis of the bony orbit.

In other words, in its primary position, the eye is significantly adducted. This will become important when we start assessing individual muscle movements in just a few moments, because all four of the recti... rectus extraocular muscles are aligned with the long axis of the bony orbit and, as we will see, relative amounts of adduction or abduction of the eyeball can alter some of their functions. We're almost ready to start assigning specific movements to the individual extraocular muscles, but first there is one final relationship to establish that will help us to visualize muscle functions. The distal insertions of all four of the rectus muscles are anterior to the horizontal axis of the eyeball.

In contrast, the two oblique muscles have distal insertions posterior to the same axis. Understanding these insertions will greatly help in making sense of the muscles'functions. Now let us consider the six basic movements that the eyeball is capable of.

Elevation, or looking up. Depression, or looking down. Adduction, looking in.

Abduction, or looking out. Intorsion. rolling the top of the eye medially towards the nose, and extortion, rolling the top of the eye laterally away from the nose.

Of course, these movements can and do occur in various combinations, some of which you will specifically assess during a routine examination of eye movements. For example, asking the patient to look up and out or down and in. The first four of the basic eye movements are relatively intuitive and easy to understand. The last two, intorsion and extorsion, are a little bit trickier and may or may not be assessed in a basic eye examination. Nevertheless, it's important to understand what these terms mean and why they are necessary for proper eye positioning.

The rotational movements of intorsion and extorsion are necessary to keep a viewed object stable and positioned on the appropriate part of the retina as the head is tilted from side to side. To illustrate, Imagine standing upright and looking at an arrow that is pointing superiorly. Now tilt your head 45 degrees to the right.

Does the arrow move with your head and now point at a 45 degree angle? Hopefully not. Because of intorsion and extorsion, the arrow should still appear to be pointing superiorly. In this case, the right eye has been intorted and the left eye has been equivalently extorted so that the image falls on the same part of the retina. as before the head tilt.

Obviously, our eyes have a limited range of intorsion-extorsion. They cannot spin completely around within the orbit. And if we were to stand on our head, the arrow would appear to change direction and appear to point inferiorly. Now let's look at the movements produced by each one of the extraocular muscles. We'll start with the medial and lateral rectus muscles, since they are each responsible for producing a single, straightforward eye movement.

Contraction of medial rectus causes adduction of the eye. Medial rectus is the primary adductor, though other extraocular muscles can assist in this movement. Contraction of lateral rectus causes abduction of the eye.

Lateral rectus is the primary abductor, though again, other extraocular muscles can assist in this movement. The remaining four extraocular muscles are a little bit more complex, since they are capable of producing multiple eye movements, and their primary function changes depending upon the relative position of the eye within the orbit. The primary result of contraction of superior rectus is elevation of the eye.

is most effective at elevating the abducted eye. With increasing adduction of the eye, superior rectus loses the mechanical advantage necessary for producing elevation, such that the fully adducted eye can be elevated only by the action of the inferior oblique muscle. In addition to its primary function, as an elevator of the eye, superior rectus also produces limited adduction and intorsion of the eye. The primary result of contraction of inferior rectus is depression of the eye. However, as is the case with superior rectus, the inferior rectus is most effective at depressing the abducted eye and loses the mechanical advantage necessary for depression as the eye is progressively adducted.

The fully adducted eye can be depressed only by the superior oblique muscle. In addition to its primary function as a depressor of the eye, inferior rectus also produces adduction, and extortion of the eye. The primary result of contraction of inferior oblique is extortion of the eye.

As mentioned earlier, inferior oblique also assists in elevation of the eye and is the only effective elevator of the fully adducted eye. Inferior oblique also contributes to abduction of the eye. Finally, let's consider the most misunderstood of the extraocular muscles. The primary result of contraction of superior oblique is intorsion of the eye.

Superior oblique also assists with depression of the eye and is the only effective depressor of the fully adducted eye. Superior oblique also contributes to abduction of the eye. Superior oblique is often referred to as the down and out muscle because if acting in isolation, that is, With all or most of the other muscles inactive, such as occurs with third nerve palsy, or a quote, blown third nerve, it does put the eye in the down and out position. However, as we will see, the function of superior oblique is not tested by having the patient look in the down and out direction, but rather in the down and in direction. This is because the coordinated function of other muscles, specifically lateral rectus and inferior rectus, can put the eye in the down and out position, but only superior oblique is able to depress the fully adducted eye, that is, to put the eye in the down and in position.

This discrepancy between the pure, isolated function of superior oblique and the clinical test of superior oblique function often causes confusion for students and clinicians alike. Now we're ready to understand the basic eye movement exam that tests the function of each extraocular muscle by having the patient sequentially look in each of six cardinal directions, also referred to as the six cardinal fields of gaze. These are in, up and in, down and in, out, up and out, and finally down and out.

The basic exam involves having the patient focus on an object. that is positioned 18 to 24 inches in front of their face as you move the object through a large H shape to encompass the six cardinal fields of gaze. The eyes can be examined individually or together. In our example both eyes will be tested at the same time. Begin by allowing the patient to focus on the object with both eyes in the primary position, that is looking straight ahead, neither elevated nor depressed.

Slowly move the object to the patient's left until you reach the limit of his field of view. Here the patient's left eye should be fully abducted and the right eye should be fully adducted. This position tests the function of the left lateral rectus muscle and the right medial rectus muscle. Now move the object directly superiorly. This position tests the patient's left superior rectus muscle, up and out, and the right inferior oblique muscle, up and in.

Continue by moving the object directly inferiorly to test the patient's left inferior rectus, down and out, and the right superior oblique muscle, down and in. Now return the object to the left horizontal position and slowly move it to an equivalent position on the right side. Here you can examine the function of the patient's right lateral rectus muscle, abduction, and the left medial rectus muscle, adduction. Again, raise the object directly superiorly to test the right superior rectus muscle, up and out, and the left inferior oblique muscle, up and in.

Move the object directly inferiorly to complete the exam by testing the right inferior rectus, down and out, and the left superior oblique muscle. down and in. You have now tested the six cardinal fields of gaze for each eye. There are other things that can be assessed with this basic eye exam, including smooth pursuit and the presence or absence of nystagmus. However, these are beyond the scope of this video.

While this exam involves direct assessment of individual muscle movements, it is also an efficient functional test for the three cranial nerves that innervate the extraocular muscles. And in fact, disturbed eye movements result more often than not from central or peripheral nerve disorders rather than from mechanical causes such as muscle entrapment or trauma. Let's briefly go over what to expect with complete disruption of these cranial nerves.

For the sake of simplicity, we will assume damage to the brainstem motor nucleus of each nerve rather than a more distal lesion is the cause of the deficit. Complete disruption of oculomotor nerve function or third nerve palsy, results in paralysis of four extraocular muscles, superior rectus, inferior rectus, medial rectus, and inferior oblique. Patients with this disorder present with the ipsilateral eye stuck in the down and out position due to the fact that tonic activity of the intact lateral rectus muscle fully abducts the eye because it is no longer opposed by the medial rectus muscle.

Further, the eye is depressed. because the action of superior oblique is no longer opposed by the elevation normally provided to the abducted eye by the superior rectus muscle. Because lateral rectus and superior oblique are the only remaining functional muscles, the eye is unable to move from this position.

Complete disruption of the trochlear nerve function, or fourth nerve palsy, results in paralysis of the contralateral superior oblique muscle. The trochlear nerve is the only motor cranial nerve that decussates or crosses to the other side. Patients with this disorder are unable to depress the affected eye when it is adducted or in the primary position due to the fact that the intact inferior rectus loses the ability to depress the eye as it is increasingly adducted.

In addition, these patients are unable efficiently to intort the affected eye. Both of these lost functions can result in, quote, double vision. Many patients unconsciously compensate by tucking the chin, which eliminates the need to depress the affected eye, and tilting the head away from the affected eye, which eliminates the need to intort the affected eye.

An eye movement exam of patients with trochlear nerve palsy reveals an inability to put the affected eye in the down and in position. Finally, complete disruption of abducens nerve function, or sixth nerve palsy, causes paralysis of the ipsilateral lateral rectus muscle and an inability to fully abduct the affected eye. These patients typically experience double vision, except during near vision when both eyes are directed inward. Eye movement exam reveals an inability to abduct the affected eye beyond the primary position.

Some of these patients compensate by turning their head toward the injured side, which allows them to adduct the affected eye and pair it with the normal eye, which will be abducted to a corresponding degree.

Transcript for:Anatomy of Eye Movement for Assessment

Transcript for:
Anatomy of Eye Movement for Assessment