A nurse is assessing a client’s cranial nerves as part of a neurological examination. Which of the following actions should the nurse take to assess cranial nerve III?
A.
Eliciting the gag reflex
B.
Testing visual acuity
C.
Observing for facial symmetry
D.
Checking the pupillary response to light
The Correct Answer and Explanation is:
The correct answer is D. Checking the pupillary response to light.
Explanation:
Cranial nerve III, also known as the oculomotor nerve, is primarily responsible for controlling most of the eye’s movements, including the constriction of the pupil and maintaining an open eyelid. To assess the function of cranial nerve III, the nurse should evaluate the pupillary response to light, among other actions. Here’s a detailed breakdown of why this is the correct approach:
- Pupillary Response to Light:
- Function: Cranial nerve III controls the parasympathetic function of the eye, which includes the constriction of the pupil. This response is known as the pupillary light reflex.
- Assessment Method: The nurse assesses this by shining a light into the client’s eyes and observing the constriction of the pupils. A normal response involves both pupils constricting when light is directed into either eye, known as consensual reflex. This checks both the direct and consensual responses of the pupils, confirming the proper functioning of the oculomotor nerve.
- Significance: A defect in the pupillary response can indicate issues such as oculomotor nerve palsy, which might manifest as dilated pupils or impaired pupil constriction.
- Other Cranial Nerves:
- Eliciting the Gag Reflex (Option A): This action assesses cranial nerves IX (glossopharyngeal) and X (vagus), not cranial nerve III. It evaluates the function of the throat muscles and sensation in the back of the throat.
- Testing Visual Acuity (Option B): This evaluates cranial nerve II (optic nerve), which is responsible for vision. Visual acuity tests the clarity of vision but does not assess the function of cranial nerve III.
- Observing for Facial Symmetry (Option C): This is relevant for cranial nerve VII (facial nerve). It evaluates facial movements and expressions, not the function of cranial nerve III.
In summary, assessing the pupillary response to light is a direct and effective way to evaluate the function of cranial nerve III. This test helps in diagnosing potential issues with the nerve’s ability to control pupil constriction and eye movement.