Oculomotor - Stanford - Exam 1 Flashcards
Axons of retinal ganglion cells make up the afferent limb of this pathway. Upon exiting the retina, retinal ganglion cell axons follow the usual route (i.e., optic nerve, optic chiasm, optic tract), however, instead of synapsing in the LGN, the axons of cells involved in the pupillary light reflex continue on to enter the ____ of the ___ ___ enroute to their site of termination, the ___ nucleus.
The ___ limb begins at the pretectal nucleus. Fibers exit the ___ __ and project ___ to the ___-___ nucleus, the preganglionic parasympathetic component of the oculomotor complex. The preganglionic fibers exit as part of Cranial Nerve III (oculomotor nerve) enroute to the ___ ganglion (located near the eye within the orbit). The postganglionic fibers enter the eye as the ___ ciliary nerve and innervate the __ ___ (constrictor).
Axons of retinal ganglion cells make up the afferent limb of this pathway. Upon exiting the retina, retinal ganglion cell axons follow the usual route (i.e., optic nerve, optic chiasm, optic tract), however, instead of synapsing in the LGN, the axons of cells involved in the pupillary light reflex continue on to enter the brachium of the superior colliculus enroute to their site of termination, the pretectal nucleus.
The efferent limb begins at the pretectal nucleus. Fibers exit the pretectal nucleus and project bilaterally to the Edinger-Westphal nucleus, the preganglionic parasympathetic component of the oculomotor complex. The preganglionic fibers exit as part of Cranial Nerve III (oculomotor nerve) enroute to the ciliary ganglion (located near the eye within the orbit). The postganglionic fibers enter the eye as the short ciliary nerve and innervate the pupillary sphincter (constrictor).
The pretectal nucleus is found at the level of the __ __, just anterior to the __ colliculus and just posterior to the thalamus (i.e., the midbrain-diencephalon junction).
The pretectal nucleus is found at the level of the posterior commissure, just anterior to the superior colliculus and just posterior to the thalamus (i.e., the midbrain-diencephalon junction).
From a clinical perspective, the most important aspect of the anatomy of the pathway is the bilaterality of the projection from the pretectal nucleus to the EW nucleus. Because the efferent limb of the pathway is ___, when light is shone in one eye (with a light pen during an examination), not only does the pupil of the illuminated eye constrict, the pupil of the other eye does as well. Constriction of the illuminated pupil is referred to as the ___ response. Constriction of the other pupil is called the ___ response.
From a clinical perspective, the most important aspect of the anatomy of the pathway is the bilaterality of the projection from the pretectal nucleus to the EW nucleus. Because the efferent limb of the pathway is bilateral, when light is shone in one eye (with a light pen during an examination), not only does the pupil of the illuminated eye constrict, the pupil of the other eye does as well. Constriction of the illuminated pupil is referred to as the direct response. Constriction of the other pupil is called the consensual response. Use the slide to trace the pathways that produce the direct and consensual responses.
Abnormal pupillary light reflex Figure
The top panel of Figure 3 shows a ___ response: illuminating the subject’s right eye produces both a __ and a __ response. The bottom panel shows an ___ response. In this case, illuminating the subject’s left eye fails to produce constriction of either pupil.
This pattern of result, i.e., direct (right eye) and consensual (left eye) response when the right eye is illuminated but no response in either eye when the left eye is illuminated, points to a deficit in the ___ limb of the pathway originating on the left side. Such a patient would be diagnosed as having a ___. The mirror symmetric pattern would, of course, be diagnostic of a right afferent pupillary defect (RAPD).
Abnormal pupillary light reflex
The top panel of Figure 3 shows a normal response: illuminating the subject’s right eye produces both a direct and a consensual response. The bottom panel shows an abnormal response. In this case, illuminating the subject’s left eye fails to produce constriction of either pupil.
This pattern of result, i.e., direct (right eye) and consensual (left eye) response when the right eye is illuminated but no response in either eye when the left eye is illuminated, points to a deficit in the afferent limb of the pathway originating on the left side. Such a patient would be diagnosed as having a left afferent pupillary defect (LAPD). The mirror symmetric pattern would, of course, be diagnostic of a ___.
This slide illustrates the location of a lesion that would produce a right afferent pupillary defect. In this case the lesion completely encompasses the right optic nerve. As a result, the pretectal nuclei fail to receive any input from the right retina and illuminating the right eye produces no response. This patient is effectively blind in the right eye. Projections from the right eye are intact.
This slide illustrates the location of a lesion that would produce a right afferent pupillary defect. In this case the lesion completely encompasses the right optic nerve. As a result, the pretectal nuclei fail to receive any input from the right retina and illuminating the right eye produces no response. This patient is effectively blind in the right eye. Projections from the right eye are intact.
Afferent defects need not be all-or-none, as in the case of total blindness in one eye. Lesions of the ____ limb that produce partial visual impairment are associated with differences in the magnitude of the light reflex induced by illumination of the two eyes. Inflammation of the __ __ (optic neuritis) is condition that might lead to a partial visual impairment.
This slide shows the results of an examination that would indicate a partial afferent defect on the right side. Weaker (constricts to 4mm vs 2mm) direct and consensual responses produced when light is shone in the right eye (bottom panel) indicates that the right afferent limb has less light detecting capability than the left.
Afferent defects need not be all-or-none, as in the case of total blindness in one eye. Lesions of the afferent limb that produce partial visual impairment are associated with differences in the magnitude of the light reflex induced by illumination of the two eyes. Inflammation of the optic nerve (optic neuritis) is condition that might lead to a partial visual impairment.
This slide shows the results of an examination that would indicate a partial afferent defect on the right side. Weaker (constricts to 4mm vs 2mm) direct and consensual responses produced when light is shone in the right eye (bottom panel) indicates that the right afferent limb has less light detecting capability than the left.
A lesion of the efferent limb of the pathway is one that is located anywhere from the ___ to the __ ___ nerve. A lesion of the ___ limb will obliterate (or diminish) both the direct and consensual responses for the pupil of one eye. Note that this pattern is quite distinct from that produced by a lesion of the __ limb.
The most common efferent pupillary defect is ___ syndrome, which is associated with ___ of the intraocular muscles innervated by the ciliary ganglion (both the pupillary sphincter and the ciliary muscle). Viral ciliary ganglionitis is thought to be a cause.
A lesion of the efferent limb of the pathway is one that is located anywhere from the pretectum to the short ciliary nerve. Use the pathway figure to confirm that a lesion of the efferent limb will obliterate (or diminish) both the direct and consensual responses for the pupil of one eye. Note that this pattern is quite distinct from that produced by a lesion of the afferent limb.
The most common efferent pupillary defect is Adie’s syndrome, which is associated with denervation of the intraocular muscles innervated by the ciliary ganglion (both the pupillary sphincter and the ciliary muscle). Viral ciliary ganglionitis is thought to be a cause.
The pupillary light reflex is mediated by the pupillary sphincter, however, abnormal pupillary light responses can also result from lesions that affect the action of the pupillary dilator. For example, ____ syndrome, causes a paralysis of the pupillary dilator and is characterized by a chronically __ ___on the side of the lesion. Horner’s syndrome can be produced by a lesion at various places within the __ chain.
This slide shows both the parasympathetic and sympathetic innervation of the iris. We’ve already discussed the ___ innervation of the pupillary sphincter (i.e. pretectal, EW, ciliary ganglion via CN III., to pupillary sphincter via the short ciliary nerves).
The ___ chain involves the hypothalamus and mediates effects that are secondary to arousal. One of these is dilation of the pupils. Beginning in the hypothalamus, this relatively long pathway goes into the __ ___ cord and synapses on cells in the intermediolateral zone. From there, it’s to the __ ___ ___, and then to the pupillary dilator via the __ ___ nerves.
Horner’s syndrome then could result from a central, preganglionic, or post- ganglionic lesion. Such a lesion could be secondary to a number of other problems: central vascular infarct, spinal cord damage, even a lung or breast tumor that encroaches upon the superior cervical ganglion.
The pupillary light reflex is mediated by the pupillary sphincter, however, abnormal pupillary light responses can also result from lesions that affect the action of the pupillary dilator. For example, Horner’s syndrome, causes a paralysis of the pupillary dilator and is characterized by a chronically small pupil on the side of the lesion. Horner’s syndrome can be produced by a lesion at various places within the sympathetic chain.
This slide shows both the parasympathetic and sympathetic innervation of the iris. We’ve already discussed the parasympathetic innervation of the pupillary sphincter (i.e. pretectal, EW, ciliary ganglion via CN III., to pupillary sphincter via the short ciliary nerves).
The sympathetic chain involves the hypothalamus and mediates effects that are secondary to arousal. One of these is dilation of the pupils. Beginning in the hypothalamus, this relatively long pathway goes into the cervical spinal cord and synapses on cells in the ___ zone. From there, it’s to the superior cervical ganglion, and then to the pupillary dilator via the long ciliary nerves.
Horner’s syndrome then could result from a central, preganglionic, or post- ganglionic lesion. Such a lesion could be secondary to a number of other problems: central vascular infarct, spinal cord damage, even a lung or breast tumor that encroaches upon the superior cervical ganglion.
Constriction of the pupil is a component of both of the visual reflexes discussed in this lecture. In one case, constriction occurs in response to light (pupillary light reflex) and in the other, an internally generated motor command causes the pupils to constrict (near response). In clinical texts, and perhaps on a board exam, you will come across the term _____ pupil. This is named after the physician who noted that a patient could show normal pupillary constriction associated with the near response but a poor or absent light reflex. Despite sharing part of the efferent pathway to the pupillary sphincter, anatomical differences elsewhere make it possible for a lesion to impair one without the affecting the other. In the past, light-near dissociation was a good diagnostic for ___ and is also a component of syndromes associated with midbrain lesions (e.g. Parinaud’s syndrome).
Slide illustrates a light-near dissociation. The top panel shows a poor light reflex (eyes remain dilated) and normal pupillary constriction associated with the near reflex (bottom panel).
Constriction of the pupil is a component of both of the visual reflexes discussed in this lecture. In one case, constriction occurs in response to light (pupillary light reflex) and in the other, an internally generated motor command causes the pupils to constrict (near response). In clinical texts, and perhaps on a board exam, you will come across the term Argyll-Robertson pupil. This is named after the physician who noted that a patient could show normal pupillary constriction associated with the near response but a poor or absent light reflex. Despite sharing part of the efferent pathway to the pupillary sphincter, anatomical differences elsewhere make it possible for a lesion to impair one without the affecting the other. In the past, light-near dissociation was a good diagnostic for neurosyphillus and is also a component of syndromes associated with midbrain lesions (e.g. Parinaud’s syndrome).
Slide illustrates a light-near dissociation. The top panel shows a poor light reflex (eyes remain dilated) and normal pupillary constriction associated with the near reflex (bottom panel).
__ __ are due to compromised function of the cranial nerves that innervate the extraocular muscles. Some common causes include diabetic neuropathy, head trauma (shears the nerves), and aneurysm (pressure on nerves).
Gaze palsies are due to compromised function of the cranial nerves that innervate the extraocular muscles. Some common causes include diabetic neuropathy, head trauma (shears the nerves), and aneurysm (pressure on nerves).
Patients with gaze palsy show ___ gaze (the two eyes are misaligned and do not move in a coordinated fashion) and diplopia (double vision).
Misalignment of the two eyes causes visual images to fall on spatially mismatched regions of the left and right retinae, thus leading to ___
Patients with gaze palsy show disconjugate gaze (the two eyes are misaligned and do not move in a coordinated fashion) and diplopia (double vision). Misalignment of the two eyes causes visual images to fall on spatially mismatched regions of the left and right retinae, thus leading to double-vision.
First one is ___ palsy
Second one is __ palsy
First - Abducens..patient can’t move the eye alterally.
Second - Trochlear palsy
This slide illustrates the gaze misalignment that would be produced by an abducens nerve (CNVI) palsy of the right eye (top row) and for a trochlear nerve palsy of the right eye (bottom row). For the abducens nerve palsy (top), the reduced efficacy of the right lateral rectus causes the right eye to deviate in the nasal direction as compared to the left (normal) eye. The bottom row shows the effect of a trochlear nerve (CNIV) palsy of the right eye. The trochlear nerve innervates the superior oblique which is responsible for rotation downward and intorsion. When the superior oblique is impaired, the eye deviates upward and extorts (rotates clockwise from the patient’s perspective) as compared to the normal eye.
What type of palsy is this?
Trochlear palsy.
The superior oblique is unable to pull the eye down, so it shoots up every time you bring the eye medially to the right (if they have a right eye troch. palsy)
What type of palsy is this? Why does it happen?
This is oculomotor nerve palsy (CN III)
The eye is down and out because lateral rectus muscles are OK (CN VI), and superior oblique muscles are OK (CN IV). The patient is unable to move the eye medially, so the eye is pulled diagnally down from the lateral pull and superior oblique pull.
This slide summarizes the locations and connections of the cranial nerve nuclei associated with gaze control. It is important to note that, in addition to innervating the lateral rectus muscle (via CNVI), the abducens nucleus indirectly influences the action of the ___ rectus on the opposite side to allow for coordinated conjugate movements. This is accomplished via a projection that crosses the midline (shown in purple) and terminates in the ___ nucleus). These so-called internuclear fibers travel in what’s called the ____ ___ ____ enroute from the abducens to the __ nucleus. As we’ll see shortly, disruption of these internuclear fibers creates a clinical condition known as __ __
This slide summarizes the locations and connections of the cranial nerve nuclei associated with gaze control. It is important to note that, in addition to innervating the lateral rectus muscle (via CNVI), the abducens nucleus indirectly influences the action of the medial rectus on the opposite side to allow for coordinated conjugate movements. This is accomplished via a projection that crosses the midline (shown in purple) and terminates in the oculomotor nucleus (III). These so-called internuclear fibers travel in what’s called the medial longitudinal fasciculus (MLF) enroute from the abducens to the oculomotor nucleus. As we’ll see shortly, disruption of these internuclear fibers creates a clinical condition known as internuclear opthalmoplegia.
What type of palsy?
Right abducens palsy
What type of palsy?
Right abducens nucleus (right lateral gaze palsy)
What type of palsy?
It could be a right abducens nucleus palsy (right lateral gaze) or a PPRF lesion.
The paramedian pontine reticular formation, also known as PPRF or paraabducens nucleus, is part of the pontine reticular formation, a brain region without clearly defined borders in the center of the pons. It is involved in the coordination of eye movements, particularly horizontal gaze and saccades.
What type of palsy?
Lesion 4 – left internuclear opthalmoplegia (impaired adduction of left eye) due lesion of internuclear fibers in left MLF.
What kind of palsy? Explain
Left MLF and left abducens nucleus lesion
This is very extensive. It captures the internuclear fibers but also captures the abducens nucleus on the same side of those internuclear fibers. So it is impairing those internucelar fibers that orginated from the abducens on the opposite side, but also the abducens nucleus on that side which gives rise the other internucelar fibers going to the other side, as well as the fibers going out of CN VI to the LR muscles. So now we have three muscles inmpaired and onyl one intact. The only thing the patient can do is rotate the right eye outwards, because the only thing that is still in tact are the fibers going to the lateral rectus on that side. So if you look, leftward gaze – nothing happens. If we go for rightward gaze, you can see that the right eye can rotate outwards but nothing else can happen. So this is called a 1 1/2 lesion.
•Lesion 5 – so-called 1 ½ lesion. The lesion shown here is extensive enough to encroach upon the both sets of internuclear fibers (both MLFs) as well as the abducens nucleus on the left side. In this case, we have bilateral internuclear opthalmoplegia and a unilateral deficit in abduction (left eye). The only movement this patient would be able to make is that of abducting the right eye.
What does this patient have?
1 1/2 palsy
The lesion shown here is extensive enough to encroach upon the both sets of internuclear fibers (both MLFs) as well as the PPRF and abducens nucleus of one side. In this case, we have bilateral internuclear opthalmoplegia and a unilateral deficit in abduction (right eye). The only movement this patient would be able to make is that of abducting the left eye. She is unable to look to the right at all (top photo). Upon looking to the left (bottom photo), she is only able to abduct the left eye.
What type of sydrome is this?
1 1/2 sydrome.
MLF lesion and abducens lesion
What is wrong with this patient?
Example of right internuclear opthalmoplegia: This woman is first asked to look to her right (top photo), which she does fine. She is then asked to look to the left (bottom photo). Note that the left eye abducts just fine, but the right eye shows incomplete adduction (Compare to above adduction).
The lesion is one that affects the internuclear fibers that run in the MLF from the abducens to the oculomotor complex.
When we want to move our eyes to something that is interesting to us in the world, that motor command originates in the cortex, called the supranuclear . How do we know that a gaze problem is not way up here than in the brain stem?
There is a simple way to tell.
This patient has a __ __ palsy as a result of a stroke. Supra nuclear refers to something above the cranial level. This patient is being asked to look to the right but he cannot look to the right. He’s asked to look at the paper clip but he cannot. This could be a brainstem lesion, a 1 1/2 lesion, etc. How do we know it is not though?
What the doctor is doing, is rotating the man’s head. What happens is, there is a reflex called the ____ ____. When we rotate our heads, the eyes tend to counter roate to maintain stable gaze. You can see that the patient has the ability to maintain stable gaze. So, on command, he cannot deviate to the right because the control to move them is lost. But the involuntary VOR is intact. This tell us that brainstem is OK, CN is OK, motor nuclei are OK. This has got to be something above the level of the brain stem – a higher cognitive function. Note that the system is ___ such that activity in the right FEF corresponds to a leftward saccade and vice versa.
When we want to move our eyes to something that is interesting to us in the world, that motor command originates in the cortex, called the supranuclear . How do we know that a gaze problem is not way up here than in the brain stem?
There is a simple way to tell.
This patient has a supranuclear gaze palsy as a result of a stroke. Supra nuclear refers to something above the cranial level. This patient is being asked to look to the right but he cannot look to the right. He’s asked to look at the paper clip but he cannot. This could be a brainstem lesion, a 1 1/2 lesion, etc. How do we know it is not though?
What the doctor is doing, is rotating the man’s head. What happens is, there is a reflex called the vestibulo-ocular reflex. When we rotate our heads, the eyes tend to counter roate to maintain stable gaze. You can see that the patient has the ability to maintain stable gaze. So, on command, he cannot deviate to the right because the control to move them is lost. But the involuntary VOR is intact. This tell us that brainstem is OK, CN is OK, motor nuclei are OK. This has got to be something above the level of the brain stem – a higher cognitive function. Note that the system is contralateralized such that activity in the right FEF corresponds to a leftward saccade and vice versa.
