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Clinical Examples (continued)

Example 6

Symptoms. A patient who is suffering from the late stages of syphilis is sent to you for a neuro-ophthalmological work-up. His vision is normal when corrected for refractive errors. He has normal ocular mobility and his eyelids can be elevated and depressed at will. Examination of his pupillary responses indicates a loss of the pupillary light reflex (no pupil constriction to light in either eye) but normal pupillary accommodation response (pupil constricts when the patient's eyes are directed from a distant object to one nearby).

Observation: You observe that the patient has normal vision but that his pupils

• do not respond when light is directed into the either of his eyes
  
• do respond during accommodation
  

You conclude that his eye's functional loss is

• not sensory (his vision is normal)
  
• motor (the pupillary light responses in both eyes are absent)
  
• higher-order motor (because he has a normal pupillary accommodation response)
  

Pathway(s) affected: You conclude that structure(s) in the

• accommodation pathway have not been damaged (Figure 7.14)
  
• pupillary light reflex pathway have been damaged (Figure 7.11)
  

Side & Level of damage: As the pupillary response deficit

• does not involve a sensory loss
  
• does not involve the pupil accommodation response
  
• involves only the pupillary light reflex response
  

Conclusion: You conclude that the damage

• involves the pretectal area bilaterally
• spared the supraoculomotor area
  
• produced the Argyll Robertson response
  

	Figure 7.14 The accommodation pathway includes the supraoculomotor area, which functions as a "higher-order" motor control stage controlling the motor neurons and parasympathetic neurons (i.e., the Edinger-Westphal neurons) of the oculomotor nucleus. This area was spared by syphilis.

In the Argyll Robertson response, there is an absence of the pupillary light reflex with a normal pupillary accommodation response. The Argyll Robertson response is attributed to bilateral damage to pretectal areas (which control the pupillary light reflex) with sparing of the supraoculomotor area (which controls the pupillary accommodation reflex).

The accommodation response involves many of the structures involved in the pupillary light response and, with the exception of the pretectal area and supraoculomotor area, damage to either pathway will produce common the symptoms. The most common complaint involving the accommodation response is its loss with aging (i.e., presbyopia). Recall that presbyopia most commonly results from structural changes in the lens which impedes the lens accommodation response.

Summary

This chapter described three types of ocular motor responses (the eye blink, pupillary light and accommodation responses) and reviewed the nature of the responses and the effectors, efferent neurons, higher-order motor control neurons (if any), and afferent neurons normally involved in performing these ocular responses. Table I summarizes these structures and the function(s) of these ocular motor responses. Readers should understand the anatomical basis for disorders that result from damage to components of neural circuit controlling these responses.

Table I Classification of Consensual Ocular Responses & Their Motor Control Structures
Ocular Responses	Function	Afferent Input* & Motor Control Structures
Eye Blink Reflex	Protects cornea from contact with foreign objects	Free Nerve Endings in cornea that are afferent endings of the Trigeminal Nerve, Ganglion, Root & Spinal Trigeminal Tract* Spinal Trigeminal Nucleus* Reticular Formation (bilaterally to) Facial Motor Nuclei & Facial Nerves Orbicularis Oculi
Pupillary Light Reflex	Decreases pupil size (constriction) – reduces the amount of light that enters the eye.	Retina, Optic Nerve, Chiasm & Tracts and Brachium of Superior Colliculus* Pretectal Areas of Midbrain (bilaterally to) Edinger-Westphal Nuclei & Oculomotor Nerves Ciliary Ganglia & Short Ciliary Nerves Iris Sphincters
Pupillary Accommodation Lens Accommodation	Increases depth of focus of eye lens system Increases refractive power of lens	Visual System* including Visual Association Cortex Supraoculomotor Nuclei (bilaterally to) Edinger-Westphal Nuclei & Nerve III Ciliary Ganglia & Short Ciliary Nerves Iris Sphincters & Ciliary Muscles
Convergence	Eyes directed nasally during accommodation	Visual System* including Visual Association Cortex Supraoculomotor Nuclei (bilaterally to) Oculomotor Nuclei Medial Rectus Muscles
* Afferent structures proving sensory input.

 

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