Final answer:
Unilateral oculomotor palsy with pupil involvement is typically caused by damage to the oculomotor nerve or its nucleus, the Edinger-Westphal nucleus, which may result from an aneurysm, tumor, or trauma. Testing the pupillary light reflex helps differentiate if the damage is in the oculomotor system or the optic nerve.
Step-by-step explanation:
A cause of unilateral oculomotor palsy with pupil involvement, which affects the movement of one eye and causes changes in the pupil, is damage to the oculomotor nerve or its nucleus, the Edinger-Westphal nucleus. Damage can occur due to various conditions like an aneurysm, tumor, or trauma. The classic signs of oculomotor nerve damage include an inability to move the eye upward, downward, or inward, drooping of the eyelid (ptosis), and a dilated pupil that does not respond normally to light.
Light shined in one eye causing constriction only of the opposite pupil indicates damage to the ipsilateral oculomotor nerve, since the direct reflex is lost, but the consensual reflex remains intact. Conversely, if light shined in one eye results in no pupillary change, but the opposite eye reacts normally when light is applied, the problem could be with the optic nerve on the side not responding. These reflex tests help differentiate whether the issue lies within the oculomotor system or the optic nerve.