The spared pupil does not close the assessment

A fictional adult develops a new isolated ocular-motor deficit with ptosis and diplopia. The initial pupil examination appears relatively preserved. The referral note does not fully document external motility, onset, pain, progression, vascular history or other neurological signs. One trainee declares that a spared pupil proves a benign microvascular cause and that no further assessment is needed. Another clinician asks for a complete acquired-third-nerve-palsy evaluation and considers the relevant neurovascular imaging pathway. The case does not establish an aneurysm, but it also does not supply evidence sufficient to exclude one. The educational task is to distinguish a pattern that changes probability from a rule that guarantees diagnostic safety.