Anisocoria or unequal pupil size may be attributed to a variety of issues and warrants further evaluation. This includes aneurysm, brain
tumor or abscess
, excess pressure in one eye caused by glaucoma, increased intracranial pressure, infection, seizure, as well as migraine headache. To determine the underlying cause, complete physical examination as well as imaging studies such as CT scan may need to be done. Take care and do keep us posted with the MRI result. Best regards.