Relative Pupil Sparing Third Nerve Palsies-To Angiogram or Not?

The rule of the Pupil has dictated the approach to third nerve palsies in neuro-ophthalmic practice for years. The rule states that when an aneurysm is the cause of the palsy, the pupil will be dilated and sluggish. Conversely, if the pupillary size and response is normal, aneurysm is unlikely to be the cause of the palsy. In cases of relative pupillary sparing (i.e. when the pupil is only partially involved in a complete external ophthalmoplegia or when the involvement of the extraocular muscles is much greater than the degree of pupillary involvement), the appropriate management is not clearly defined.