Clinical Characteristics and Underlying Pathophysiology in 4 Subtypes of Dysthyroid Optic Neuropathy Patients

Objective: To analyze different subtypes, clinical characteristics, and pathophysiologies of dysthyroid optic neuropathy (DON) based on orbital fat and extraocular muscle (EOM) volume increases on orbital CT images. Methods: The author retrospectively reviewed the medical records of 80 patients (152 eyes) who were diagnosed with DON and treated at Anam, Guro, or Ansan hospitals of the Korea University College of Medicine from February 2006 to December 2023. Clinical features, ophthalmic examination, demographic characteristics, thyroid status, and radiographic findings from computed tomography scans (prevalence of fat or muscle volume increases) were analyzed. Results: Four groups were designated based on EOM volume (MV) and orbital fat volume (FV). Group 1 had no increase in MV or FV (5.3%, 8 eyes), group 2 had increased FV only (8.66%, 13 eyes), group 3 had an increase in MV only (52.6%, 80 eyes), while group 4 had both MV and FV increase (33.6%, 51 eyes). Patients in group 1 were younger and had low diplopia scores than patients in the other groups. Decreases in visual acuity, color vision abnormalities, diplopia score, and apical crowding were less frequent in groups 1 and 2 than groups 3 and 4 ( P =0.000). Patients in groups 3 and 4 had significantly more apical crowding and higher diplopia scores and CAS scores than patients in groups 1 and 2 ( P =0.000 and 0.013, respectively). The number of patients who underwent decompression surgery was significantly higher in groups 3 and 4 than groups 1 and 2 ( P =0.000). Conclusion: Extraocular muscle enlargement occurred in 86% of DON patients and compression of the optic nerve due to enlargement of EOMs at the orbital apex is the main cause of DON. Optic nerve stretch and vascular insufficiency due to increased orbital pressure are other potential mechanisms underlying DON in groups without an increase in FV or MV. Although decreased visual acuity, color vision abnormalities, and diplopia were less frequent in these groups, greater attention should be paid to the timely diagnosis of DON.