Pearls: diplopia.

Double vision may arise from ocular, neurologic, or extraocular muscle disorders. The approach to patients with diplopia requires a systematic approach to the history and the physical examination. There are many challenges in the evaluation of diplopia, ranging from the patient's mental status to the fine points of the examination. This article provides a process for interviewing and examining these patients, explaining the rationale and differential diagnosis of various clinical presentations. Common causes of monocular and binocular diplopia are addressed by the pattern of diplopia described by the patient. The examination and the interpretation of examination findings are presented by incorporating the "upside-down-and-backwards" concept. This review offers some Pearls-perhaps even diamonds-on evaluating patients who complain of diplopia, as well as those who have eye movement abnormalities but can't articulate their symptoms.