In this issue, Lustbader and Miller1 describe a 65-year-old hypertensive woman with an isolated, pupil-sparing third nerve palsy and complete paralysis of extraocular muscles that were caused by a basilar artery aneurysm. The case reached these pages because it violates The Rule of the Pupil in Third Nerve Palsy and forces a reexamination of how the rule applies to the treatment of such patients.
See also p 583.
The rule states that when aneurysms compress the oculomotor nerve, the iris sphincter will be impaired, leading to a dilated or sluggishly reactive pupil. A persuasive guideline, the rule was born in 1958 when Rucker2 reported that 62 (97%) of 64 aneurysmal third nerve palsies did not spare the pupil. In the two cases in which the sphincter was unimpaired, Rucker said that "involvement of the extraocular muscles was slight"—an important point that has often been ignored.
The rule has