Right Oculomotor Nerve Palsy: Clinical Manifestations
The most likely symptom of a right oculomotor (third cranial) nerve palsy is diplopia looking to the left (option B). According to the American Academy of Ophthalmology, patients with oculomotor nerve palsy experience horizontal and vertical diplopia, which is most pronounced when looking in the direction opposite to the affected side 1.
Clinical Presentation of Right Oculomotor Nerve Palsy
Eye Position and Movement
- The affected eye deviates "down and out" due to unopposed action of the lateral rectus (CN VI) and superior oblique (CN IV) muscles 1
- This results in the eye being typically abducted and infraducted (looking down and outward) 1
- Option C (Eye looking down) is partially correct but incomplete, as the eye also deviates outward
Pupillary Involvement
- In pupil-involving CN III palsy, the pupil is dilated (mydriasis), not constricted 1
- Option A (Miosis) is incorrect as miosis refers to pupillary constriction, which is the opposite of what occurs in oculomotor nerve palsy
Diplopia
- Diplopia (double vision) occurs due to misalignment of the visual axes
- This is most pronounced when looking in the direction opposite to the affected side - in this case, when looking to the left 1
- This makes option B the correct answer
Other Features (Not Listed in Options)
- Ptosis (drooping of the upper eyelid) is common but not mentioned in the options 2
- Limited or absent adduction, elevation, and depression of the affected eye
Why Option D is Incorrect
- Conjugate gaze palsy refers to the inability to move both eyes together in the same direction
- This occurs with lesions of the brainstem gaze centers or pathways, not with isolated cranial nerve palsies
- Oculomotor nerve palsy causes a disconjugate gaze problem (eyes moving differently from each other)
Clinical Pearls
- The presence of pupillary involvement (mydriasis) in CN III palsy is a critical diagnostic feature that may indicate compression by an aneurysm, requiring urgent neuroimaging 1
- In vascular causes of CN III palsy, pupillary involvement may be present but typically with less than 1mm difference in pupillary diameter 3
- Approximately 90% of patients with CN III palsy due to vascular causes recover completely within 6 months 3
In summary, diplopia looking to the left (option B) is the most characteristic symptom of right oculomotor nerve palsy, as it represents the functional consequence of the misalignment caused by the paralysis of the extraocular muscles innervated by the right third cranial nerve.