7. Ocular Motor Systems
Part 4 of 5

Valentin Dragoi, Ph.D.
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Clinical Examples (continued)

Symptoms.  The patient complains of pain in her left eye. Her left pupil appears dilated and is not reactive to light directed at either the left or right eye (Figure 7.10).  The right pupil appears normal in size and reacts to light when it is directed in the right or left eye.  Both eyelids can be elevated and lowered and both eyes exhibit normal movement. Touch, vibration, position and pain sensations are normal over the entire the body and face.  There are no other motor symptoms.

Observation: You observe that the patient has 

• a left pupil that does not react to light directly or consensually
• a right pupil that reacts to light directly and consensually
• normal eye movements

You conclude that his left eye's functional loss is

• not sensory (the right pupil reacts to light directed at the left eye)
• a motor dysfunction

Pathway(s) affected:  You conclude that structures in the following motor pathway have been affected

• the pupillary light reflex pathway  (Figure 7.11)

Figure 7.11

The pupillary light reflex pathway involves the optic nerve and the oculomotor nerve and nuclei.

Side & Level of damage:  As the pupillary light reflex loss

• involves only one eye
• involves only motor function
• does not involve eyelid or ocular motility
• is limited to pupil constriction in the left eye

Conclusion: You conclude that the damage

• involves the motor innervation of the left iris sphincter²
• involves structures peripheral to the oculomotor nucleus (i.e., eye movement unaffected)
• does not involve the oculomotor nerve
• involves the ciliary ganglion  or the short ciliary nerve
• is on the left side (i.e., the symptoms are ipsilesional)

Parasympathetic Innervation of the Eye.  Section of the parasympathetic preganglionic (oculomotor nerve) or postganglionic (short ciliary nerve) innervation to one eye will result in a loss (motor) of both the direct and consensual pupillary light responses of the denervated eye. Section of the left short ciliary nerve or a benign lesion in the left ciliary ganglion  will result in no direct response to light in the left eye and no consensual response in the left eye when light is directed on the right eye (a.k.a., tonic pupil).  When the damage is limited to the ciliary ganglion or the short ciliary nerve, eyelid and ocular mobility are unaffected. 

Symptoms.  The patient presents with a left eye characterized by ptosis, lateral strabismus, and dilated pupil.  When asked to rise his eyelids, he can only raise the lid of the right eye.  When asked to close both eyes, both eyelids close fully.  His left pupil does not react to light directly or consensually (Figure 7.12).  When asked to look to his right, his left eye moves to a central position, but no further.  The right eye is fully mobile.  When the patient is asked to look straight ahead, you note his left eye remains directed to the left and depressed.  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.

Observation:You observe that the patient 

• has not lost cutaneous sensation in the face area
• has a left ptosis
• cannot adduct his left eye (i.e., move it toward the nose)
• has a left dilated pupil that is non reactive to light in either eye

You conclude that his left eye's functional loss is

• not sensory
• a lower motor neuron dysfunction
• involving an autonomic dysfunction

Pathway(s) affected:  You conclude that structures in the following motor pathway have been affected

• the pupillary/oculomotor pathway (Figure 7.11)

Side & Level of damage:  As the ocular loss involves

• only motor function
• both reflex and voluntary motor functions
• both somatic and autonomic functions
• only the left eye

Conclusion: You conclude that the damage 

• involves the oculomotor nerve
• is a lower motor neuron paralysis of the superior levator palpebrae
• is a lower motor neuron paralysis of the medial, superior & inferior rectus muscles and inferior oblique muscles of the eye
• is an autonomic disorder involving the axons of the Edinger-Westphal nucleus
• is on the left side (i.e., the symptoms are ipsilesional)

The Oculomotor Nerve. Section of the oculomotor nerve produces a non-reactive pupil in the ipsilesional side as well as other symptoms related to oculomotor nerve damage (e.g., ptosis and lateral strabismus). Section of the oculomotor nerve on one side will result in paralysis of the superior levator palpebrae, which normally elevates the eyelid.  It will also paralyze the medial, superior & inferior rectus muscles and the inferior oblique, which will allow the lateral rectus to deviate the eye laterally and the superior oblique to depress the eye.  The parasympathetic preganglionic axons of the Edinger-Westphal nucleus, which normally travel in the oculomotor nerve, will be cut off from the ciliary ganglion, disrupting the circuit normally used to control the iris sphincter response to light.

Symptoms.  The patient complains of reduced vision in the left eye.   Pupil size in both eyes appears normal.  However, both pupils do not appear to constrict as rapidly and strongly when light is directed into his left eye (Figure 7.13).  That is, compared to the response to light in the left eye, light in the right eye produces a more rapid constriction and smaller pupil in both eyes.   Physical examination determines that touch, vibration, position and pain sensations are normal over the entire the body and over the lower left and right side of his face. 

Observation:You observe that the patient's pupils

• respond when light is directed into either eye
• has weaker direct and consensual responses to light directed in the left eye

You conclude that his left eye's functional loss is

• not motor
• sensory (because the responses in both eyes are weaker when light is directed in the left eye)

Pathway(s) affected:  You conclude that structures in the following motor pathway have been affected

• the pupillary light reflex pathway (Figure 7.11)

Side & Level of damage:  As the pupillary light response deficit involves

• only stimulation of one eye
• a sensory loss
• the left eye

Conclusion: You conclude that the damage 

• is in the afferent limb of the pupillary light response
• involves the optic nerve or retina
• is on the left side (i.e., the symptoms are ipsilesional)
• produced a left pupillary afferent defect

The Optic Nerve.  Partial damage of the retina or optic nerve reduces the afferent component of the pupillary reflex circuit.  The reduced afferent input to the pretectal areas is reflected in weakened direct and consensual pupillary reflex responses in both eyes (a.k.a., a relative afferent pupillary defect). 

Section of one optic nerve will result in the complete loss of the direct pupillary light reflex but not the consensual reflex of the blinded eye.  That is, if the left optic nerve is sectioned, light directed on the left (blind) eye will not elicit a pupillary response in the left eye (direct reflex) or the right eye (consensual response).  However, light directed in the right eye will elicit pupillary responses in the right eye and the left (blind) eye. The effect of sectioning one optic nerve is to remove the afferent input for the direct reflex of the blinded eye and the afferent input for the consensual reflex of the normal eye.  Section of one optic tract will not eliminate the direct or consensual reflex of either eye as the surviving optic tract contains optic nerve fibers from both eyes.  However, the responses to light in both eyes may be weaker because of the reduced afferent input to the ipsilesional pretectal area.

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