CN III Oculomotor

The oculomotor nerve has two main components: somatomotor and visceral. The somatomotor component innervates the extraocular muscles to move the eyeball. These signals allow the eyes to move upward, downward, inward, and medially. Second, the oculomotor nerve carries parasympathetic fibers to the iris, causing the iris to constrict when you’re in bright light (visceral component). The oculomotor nerve is also responsible for holding the eyelids open.

Dysfunction of the third cranial nerve causes ptosis (drooping) of the eyelid. The eye may also be in abduction and turned down. If the visceral component is impaired, the papillary reflex is lost and the pupil is dilated. A lesion in the oculomotor nerve may also cause double vision (diplopia) or a “blown pupil”—a pupil that cannot constrict. If the medial rectus has become weakened, the eye will tend to drift laterally, sometimes termed a ‘lazy eye’. Due to its location, the oculomotor nerve is susceptible to damage by elevated intracranial pressure, and a blown pupil can be a sign of serious neurological trouble.

HOW IT RELATES TO THE SLP: The oculomotor nerve is important for noticing your surroundings, reading, and is used for lip reading. This cranial nerve is also important for eating and swallowing. Damage to the oculomotor nerve may affect your client’s ability to see the food they want to eat resulting in them not receiving proper nourishment. Dysfunction to the oculomotor nerve may also affect your client’s ability to maintain eye contact therefore affecting the message wanting to be communicated. Joint referencing and mutual gaze will be difficult for clients with damage to the third cranial nerve.

CN III Oculomotor Examination

• Look at pupils: shape, relative size, ptosis.
• Shine light in from the side to gauge pupil’s light reaction
  • Assess both direct and consensual responses.
    • Direct response-constriction of the illuminated pupil
    • Consensual response-constriction of the opposite pupil
      • Assess afferent pupillary defect with the swinging flashlight test, in which the light is moved back and forth between the eyes every two to three seconds.
• Afferent pupillary defect-decreased direct response caused by decreased visual function in one eye.
• During examination in response to the light the affected pupil dilates. Under normal conditions, the pupil constricts in resonse to the light.
• “Follow finger with eyes without moving head”
  • Normal conditions: the pupils constrict while fixating on an object being moved from far way to near the eyes
  • Look for failure of movement, nystagmus
  • Convergence by moving finger toward bridge of patient’s nose

Sources:

Everything Speech. (2010, December  6). Cranial nerve exam. Retrieved from http://everythingspeech.com/evaluation/cranial-nerve-exam/

Nervous: Cranial nerves exam. (n.d.). Retrieved from http://www.clinicalexam.com/pda/n_cranial_nerves_exam.htm

http://droualb.faculty.mjc.edu/Lecture%20Notes/Unit%205/cranial_nerves%20Spring%202007%20with%20figures.htm (Picture one).