Teprotumumab N01 Versus Methylprednisolone After Urgent Orbital Decompression for Dysthyroid Optic Neuropathy

Inclusion Criteria: * Able and willing to provide written informed consent. * Age 18 to 65 years. * Clinical diagnosis of thyroid eye disease (TED) with dysthyroid optic neuropathy (DON). Diagnosis of DON must meet both of the following criteria: 1. Visual dysfunction not explained by other causes, such as decreased best-corrected visual acuity, visual field defect, abnormal color vision, or relative afferent pupillary defect. 2. Imaging evidence of orbital apex crowding, optic nerve compression, or optic nerve stretching. * The study eye meets the criteria for urgent orbital decompression, defined as either of the following: 1. Poor response after rescue intravenous methylprednisolone for the current dysthyroid optic neuropathy episode, with a cumulative methylprednisolone-equivalent dose of no more than 3.0 g, defined as no improvement or continued deterioration of visual function within 1 to 2 weeks. 2. Contraindication to glucocorticoids or investigator judgment that direct urgent mechanical decompression is required. * Thyroid function is normal or mildly abnormal before enrollment, with free triiodothyronine (FT3) and free thyroxine (FT4) within 50% above or below the normal reference range when possible. * Alanine aminotransferase (ALT) no more than 1.5 times the upper limit of normal, aspartate aminotransferase (AST) no more than 3 times the upper limit of normal, and serum creatinine no more than 1.5 times the upper limit of normal. * For participants with diabetes mellitus, hemoglobin A1c (HbA1c) less than 9.0% and stable antidiabetic treatment within 60 days before enrollment. * For women of childbearing potential, a pregnancy test must be negative before enrollment. * Participants of reproductive potential agree to use effective contraception during the study and for 90 days after the last dose of study treatment. * Able and willing to comply with study treatment and follow-up procedures. Exclusion Criteria: * Orbital decompression surgery within 6 months before screening. * Bilateral dysthyroid optic neuropathy requiring urgent bilateral orbital decompression at baseline. * Cumulative preoperative methylprednisolone-equivalent dose greater than 3.0 g for the current dysthyroid optic neuropathy episode. * Systemic glucocorticoid treatment for non-thyroid eye disease within 3 months before screening with cumulative methylprednisolone-equivalent dose of 1.0 g or greater. * Tocilizumab or other systemic immunosuppressive treatment within 3 months before screening, or rituximab within 6 months before screening. * Orbital radiotherapy within 3 months before screening. * Previous treatment with teprotumumab. * Other ocular diseases that may significantly affect visual function assessment, including glaucomatous optic neuropathy, macular disease, severe cataract, or non-thyroid eye disease optic neuropathy. * Irreversible optic nerve damage in the study eye with very low potential for visual recovery, as judged by the investigator. * History of definite inner ear disease or clinically significant hearing impairment. * Severe cardiovascular disease. * Severe hepatic or renal disease. * Active infection or clinically significant infectious disease, including active hepatitis, HIV infection, syphilis, or active tuberculosis. * Active gastrointestinal ulcer. * Clinically significant abnormal blood test results, including white blood cell count less than 4.0 × 10\^9/L, platelet count less than 80 × 10\^9/L, hemoglobin less than 110 g/L in males or less than 100 g/L in females. * History of malignancy judged by the investigator to be unsuitable for enrollment. * Pregnancy or breastfeeding. * Known allergy to monoclonal antibodies, methylprednisolone, or any study drug excipient. * Uncontrolled diabetes mellitus or any other condition that, in the investigator's judgment, makes the participant unsuitable for the study.