Neuromuscular junction and mechanical causes of diplopia

In addition to supranuclear, nuclear/infranuclear, and internuclear causes of diplopia, it is important to keep in mind neuromuscular and mechanical (extraocular muscle) causes of diplopia. Myasthenia gravis (MG) is the prototypical neuromuscular junction cause of diplopia and can mimic any pupil-sparing painless cause of diplopia; the eyelids are often diagnostically helpful in MG. MG is important to recognize not only because of the diplopic-related morbidity, but also because of the disease's potential to generalize and its association with thymoma. Several diseases, including trauma, neoplasm, sinus, and osseous pathology, affect the extraocular muscles, producing mechanically related binocular diplopia. Thyroid eye disease (TED) is the most common nontraumatic orbitopathy of adults and in its most extreme form has the potential to cause compressive optic neuropathy with attendant visual loss. TED is thought to be an autoimmune disorder that may occur in hyperthyroid, hypothyroid, or even euthyroid situations and most commonly affects the inferior and medial recti (producing esodeviations and hyperdeviations). Proptosis and eyelid dysfunction, most notably eyelid lag and retraction, are diagnostically helpful. TED management begins with an assessment of thyroid status.