A 30 year old man came at the outpatient depament because he had suddenly developed double vision. On examination it was found that his right eye, when at rest was turned medially. The most likely anatomical structures involved are:
**Core Concept**
The patient's symptoms suggest an issue with cranial nerve VI, which is responsible for lateral rectus muscle innervation, controlling eye abduction. This condition is known as lateral rectus palsy or abducens nerve palsy.
**Why the Correct Answer is Right**
The abducens nerve (cranial nerve VI) runs a long course from its nucleus in the pons to its termination in the lateral rectus muscle. The nerve is susceptible to compression or damage, often due to aneurysms, tumors, or trauma. In this case, the patient's right eye is turned medially at rest, indicating a weakness or paralysis of the lateral rectus muscle, which is responsible for outward gaze.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is not relevant to the patient's symptoms. The trochlear nerve (cranial nerve IV) is responsible for innervating the superior oblique muscle, which controls downward and inward eye movement.
**Option B:** This option is incorrect because the oculomotor nerve (cranial nerve III) is responsible for innervating several extraocular muscles, including the medial rectus, inferior rectus, and inferior oblique. However, the patient's eye is turned medially, which suggests a problem with the lateral rectus muscle, not the medial rectus muscle.
**Option C:** This option is not relevant to the patient's symptoms. The trigeminal nerve (cranial nerve V) is responsible for sensory innervation of the face and motor innervation of the muscles of mastication.
**Clinical Pearl / High-Yield Fact**
In patients with abducens nerve palsy, the affected eye will be turned medially at rest, and there will be impaired outward gaze (abduction). This condition is often a sign of an underlying aneurysm or tumor.
**Correct Answer:** C.