Optic neuropathy is a serious complication occurring in 5% of patients with endocrine ophthalmopathy. It develops due to compression of the optic nerve or the vessels that feed it at the apex of the orbit by swollen and enlarged rectus muscles.
Exophthalmos is an excessive anterior displacement of the eye caused by a retrobulbar lesion or (less commonly) a shallow orbit. Asymmetry in eye protrusion is best seen by examining the patient from above and behind.