Diagnosing the underlying etiology of diplopia requires a structured approach. Double vision can arise from ocular, mechanical, or neurologic causes. A careful history can greatly improve a targeted examination. The approach to initial diagnosis and examination in cases of diplopia has been previously described. Here the authors expand upon those recommendations, and add new techniques recently described in the literature, which may influence the approach to the diplopia patient. A description of the approach to the examination of torsion is discussed. The "three-step test" in the diagnosis of vertical strabismus is discussed, and recent advances in diagnosing skew deviation with the upright-supine test are described. Mechanical strabismus due to changes in orbital anatomy is also reviewed. This review should help the reader refine the differential diagnosis of the patient with diplopia.
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