Finite Element Analysis of Extraocular Muscle and Adipose-Dominant Pathogenesis in Thyroid Eye Disease With Clinical Implications

Purpose: To compare the biomechanical mechanisms of muscle-predominant and adipose-predominant thyroid eye disease (TED) using a three-dimensional (3D) finite element analysis (FEA) model and validate findings through clinical outcomes. Methods: A 3D orbital FEA model was reconstructed from healthy computed tomography imaging. Extraocular muscle hypertrophy and adipose proliferation were simulated under fixed volumetric expansion. Optic nerve (ON) stress and globe displacement were measured across six simulation groups. For clinical validation, 36 patients with TED were retrospectively categorized as adipose type (AT) or muscle type (MT) based on muscle-to-orbital area ratios to compare dysthyroid optic neuropathy (DON) incidence. Results: Medial rectus hypertrophy generated the highest single-muscle ON stress (0.59 kPa). Muscle-predominant simulations produced higher peak ON stress than adipose-predominant simulations (1.40 vs. 0.18 kPa). Conversely, adipose expansion caused much greater globe displacement (4.34 vs. 1.53 mm), reflecting adipose-driven exophthalmos. Clinically, MT patients demonstrated a significantly higher DON rate than AT patients (83.3% vs. 22.2%, P < 0.001), aligning with FEA-predicted risk patterns. Conclusions: Muscle-predominant TED is the primary biomechanical driver of apical compression and DON risk. Adipose-predominant TED primarily causes exophthalmos with lower tractional stress on the optic nerve. Medial rectus hypertrophy is the most significant individual contributor to compressive load. Translational Relevance: These biomechanical phenotypes help clinicians identify high-risk patients with DON (MT) who require urgent apical decompression, whereas AT patients may benefit more from volume reduction strategies focused on proptosis correction.