Dysthyroid optic neuropathy: evaluation and management.

BACKGROUND: Dysthyroid optic neuropathy (DON) is a serious complication of Graves orbitopathy (GO) from optic nerve dysfunction that may result in permanent loss of vision. PURPOSE: This paper reviews the current knowledge of DON, including its pathogenesis and epidemiology, clinical and radiologic features, and management choices and outcomes. METHODS: Literature review and author retrospective case series. RESULTS: Over 90% of DON cases are related to nerve compression by enlarged extraocular muscles (EOM) while the remainder are caused by stretching of the optic nerve without compression. DON's incidence is 5-8% of GO cases. Risk factors include advancing age, male gender, smoking and diabetes mellitus, and these cases should be referred promptly to an ophthalmologist or GO clinic to rule out DON and for ongoing care. Clinical features of DON may include reduction in central and colour vision (unexplained by other ocular disorders), afferent pupil defect and/or optic disc edema. Since most cases are associated with enlarged EOM, restricted motility and soft tissue venous congestion are common. Visual fields and optical coherence tomography (OCT) help confirm the diagnosis while CT or MRI Scans show apical optic nerve compression or proptosis with optic nerve stretch. Standard therapy includes iv/oral corticosteroids (CS) with partial response in most cases, but often relapse with tapering. Radiotherapy may delay or avoid surgery and may prevent the onset of DON when combined with CS in high-risk individuals. The benefits of newer biologic targeted therapy are not clear. Orbital decompression surgery often has positive outcomes, even in cases of severe vision loss or delayed surgery. The most common surgical complication is worsening strabismus, which may worsen visual function and quality of life. In rare cases, permanent vision loss from DON may occur despite full therapy. CONCLUSIONS: Although DON may cause vision loss, most cases are reversible if recognized and managed in a timely manner.