The differential diagnosis of diplopia

BACKGROUND: Diplopia is a common symptom of interdisciplinary significance that can lead to marked impairment of function. Its causes range from harmless to life-threatening conditions that must be precisely distinguished. METHODS: For this CME review article, a PubMed search was conducted in an interdisciplinary collaboration of ophthalmologists and neurologists. RESULTS: Systematic history-taking and a structured clinical examination are the basis for topographic-anatomical diagnosis and the differentiation of peripheral and central causes. It is important to distinguish monocular from binocular diplopia. Monocular diplopia persists when one eye is covered and is not dangerous. Binocular diplopia may arise from disturbances at a variety of anatomical levels that can result from many different causes: disturbances of fusion in strabismus, diseases of the eye muscles such as thyroid eye disease or mitochondropathies, orbital trauma, impaired neuromuscular transmission in myasthenia gravis, fascicular or nuclear lesions of the three nerves that supply the extraocular muscles (oculomotor, trochlear, and abducens), supranuclear lesions "above" the cranial nerve nuclei, and cerebellar diseases. The most common causes, together accounting for ca. 70% of cases, are decompensated latent strabismus and cranial nerve palsies, followed by orbital, brainstem, and cerebellar diseases. CONCLUSION: Diplopia can be accurately diagnosed through a systematic approach that includes precise history-taking and clinical examination of eye position and eye movements. On this basis, there can be a targeted and specific search for the various underlying causes. When the patient's leading symptom is isolated diplopia, the ophthalmologist is generally the specialist to whom the primary care physician should turn next.