The differential diagnosis for this case includes mechanical and paretic causes of limited extraocular movements. A detailed history and review of systems is important to narrow down potential etiologies. The patient should be asked about a history of thyroid dysfunction, prior head or facial trauma, and prior eye surgery (particularly retinal detachment repair, scleral buckle placement, or previous retrobulbar block). A history of prior malignancy is also important to note.

Congenital or traumatic fourth nerve palsies are the most common cause of acquired vertical deviations. TED is another frequent cause of vertical diplopia, as the inferior rectus muscle is the most commonly involved muscle, followed by the medial and superior rectus muscles. Patients have decreased symptoms in downgaze and so may adopt a chin-up position to reduce symptoms of diplopia (as opposed to the head tilt frequently seen in fourth nerve palsies). TED most commonly occurs in the setting of Graves disease, but patients can also present with hypothyroidism or no prior thyroid dysfunction. Lid retraction, lid lag, temporal flare, lagophthalmos, limited abduction and resultant esotropia (due to medial rectus restriction), and proptosis can all be seen in TED, with lid lag being particularly specific.