7. Ocular Motor Systems
Part 3 of 5

Valentin Dragoi, Ph.D.
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Clinical Examples

An excellent way to test your knowledge of the material presented thus far is by examining the effects of damage to structures within the ocular motor pathways.  The observed motor loss(s) provide clues to the pathway(s) affected; and the muscle(s) and eye affected provide clues to the level of the damage.

Cranial nerve damage:  Damage to cranial nerves may result in sensory and motor symptoms.  The sensory losses would involve those sensations the cranial nerve normally conveys (e.g., taste from the anterior two thirds of the tongue and somatic sensations from the skin of the ear - if facial nerve is damaged). The motor losses may be severe (i.e., a lower motor neuron loss that produces total paralysis) if the cranial nerve contains all of the motor axons controlling the muscles of the normally innervated area. 

The cranial nerves involved in the eye blink response and pupillary response are the optic, oculomotor, trigeminal and facial nerves. 

• The optic nerve carries visual information from the eye. 
• The oculomotor nerve contains
  • lower motor axons innervating
    • extraocular muscles:  the medial, superior and inferior rectus muscles, the inferior oblique muscle,
    • eyelid muscle:  the superior levator palpebrae,
  • as well as parasympathetic preganglionic axons to the ciliary ganglion. 
• The trigeminal nerve contains
  • the 1° somatosensory afferents for the face, dura, oral and nasal cavities
  • the lower motor axons for the jaw muscles. 
• The facial nerve contains
  • the lower motor neurons innervating the superficial muscles of the face,
  • the 1° gustatory afferents to the anterior tongue
  • the parasympathetic preganglionic  axons to parasympathetic ganglia for the lachrymal and salivary glands. 

Symptoms.  The patient, who appears with a bloodshot left eye, complains of an inability to close his left eye. When asked to rise his eyebrows, he can only elevate the right eyebrow.  When asked to close both eyes, the right eyelid closes but the left eyelid is only partially closed.  Touching the right or left cornea with a wisp of cotton elicits the eye blink reflex in the right eye, but not the left eye (Figure 7.7).  However, the patient reports he can feel the cotton when it touches either eye.  He can smile, whistle and show his teeth, which indicates his lower facial muscles are functioning normally.  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 upper left face area
• does not blink when his left cornea is touched
• cannot close his left eye voluntarily

You conclude that his left eye's functional loss is

• not sensory
• a lower motor neuron dysfunction

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

• the eye blink pathway  (Figure 7.8)

Figure 7.8

The eye blink pathway involves the trigeminal nerve, spinal trigeminal tract and nucleus, the reticular formation, and the facial motor nucleus and nerve.

Side & Level of damage:  As the eye blink loss involves

• only motor function
• both reflex and voluntary motor functions
• the upper part of the face
• only one eye lid
• eyelid closure

Conclusion: You conclude that the damage involves

• the facial nerve
• a branch of the nerve innervating the upper face
• a lower motor neuron paralysis of the left orbicularis oculi
• motor innervation on the left side (i.e., the symptoms are ipsilesional)

When lower motor neurons are damaged, there is a flaccid paralysis of the muscle normally innervated.  The action of the muscle will be weakened or lost depending on the extent of the damage.  There will be a weakened or no reflex response and the muscle will be flaccid and may atrophy with time.

The Facial Nerve. Section of the facial nerve on one side will result in paralysis of the muscles of facial expression on the ipsilesional side of the face.  There will be an inability to close the denervated eyelid voluntarily and reflexively.  The eyelids may have some mobility if the oculomotor innervation to the levator is unaffected.

Symptoms.  The patient complains of a badly infected left eye.  When he is asked to close both eyes, both eyelids close.  Touching the right cornea with a wisp of cotton elicits the eye blink reflex in the both eyes (Figure 7.9, Right).  However, touching the left cornea with a wisp of cotton does not elicit the eye blink reflex in the either eye (Figure 7.9, Left). The patient cannot detect pinpricks to his left forehead.  However, he reports that pinpricks to rest of his face are painful. He can blink, wrinkle his brows, smile, and whistle and show his teeth, which indicates his facial muscles are functioning normally.  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

• responds with direct and consensual eye blink when his right cornea is touched
• can close his left eye voluntarily 
• has lost cutaneous sensation in the upper left face area
• does not blink when his left cornea is touched

You conclude that his left eye's functional loss is

• not motor
• sensory

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

• the eye blink pathway  (Figure 7.8)

Side & Level of damage:  As the eye blink loss involves

• only one eye
• a sensory loss
• the upper part of the face

Conclusion: You conclude that the damage involves

• a loss of the afferent limb of the eye blink response
• the trigeminal nerve
• a branch of the nerve innervating the upper face
• the innervation of the left side (i.e., the symptoms are ipsilesional)

The Trigeminal Nerve.  Section of the trigeminal nerve will eliminate somatosensory sensation from the face and the eye blink reflex (e.g., with section of the left trigeminal nerve, light touch of the left cornea will not produce an eye blink in the left or right eye).  However, light touch of the right cornea will elicit a bilateral eye blink.  The effect of sectioning the trigeminal nerve is to remove the afferent input for the eye blink reflex.

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