Diplopia is an uncommon but distressing result of orbital changes in Graves' disease. Significant extraocular muscle disorders occur usually when there is severe orbital involvement, as described under such terms as exophthalmic ophthalmoplegia (Brain and Turnbull1), thyrotropic exophthalmos (Mulvaney2), and infiltrative ophthalmopathy (Day3). Less frequently, muscle dysfunction is found with only minimal orbital swelling.
Limitation of ocular movement generally develops after appearance of other signs of orbital congestion—conjunctival hyperemia and edema, lid edema, exophthalmos, and increase in intraorbital pressure with resistance to palpation. Usually there is an initial limitation of upward gaze; if the restricted movement is greater in one eye, diplopia occurs. Later there may be limitation of lateral motion. In extreme cases, the eyes may become more or less fixed in a position of depression. The degree of extraocular muscle involvement is exceedingly variable. In mild forms of orbital disease, myopathy is minimal and often
LONG JC. Surgical Management of the Tropias of Thyroid Exophthalmos. Arch Ophthalmol. 1966;75(5):634-638. doi:10.1001/archopht.1966.00970050636010