Quantifying Orbital Segmentation in Thyroid Eye Disease- Fat to Muscle Ratio Correlates With Restrictive Strabismus

Area of Science:

• Ophthalmology
• Endocrinology
• Radiology

Background:

• Thyroid Eye Disease (TED) can cause restrictive strabismus due to orbital tissue changes.
• The fat-to-muscle ratio (FMR) is a potential imaging biomarker for assessing these changes.

Purpose of the Study:

• To evaluate the utility of orbital FMR in quantifying fat and muscle volumes in TED patients.
• To assess the association of FMR with restrictive strabismus and disease severity.

Main Methods:

• Retrospective analysis of orbital CT scans from 197 adult TED patients.
• Quantification of orbital fat and extraocular muscle (EOM) volumes using 3D segmentation to calculate FMR.
• Correlation analysis of FMR with strabismus, restrictive motility, Clinical Activity Score (CAS), and thyroid-stimulating immunoglobulin (TSI).

Main Results:

• Lower FMR was significantly associated with restrictive ocular motility (p < 0.001) and strabismus.
• FMR inversely correlated with strabismus angle, EOM surgery, CAS, and TSI levels.
• Lower FMR was an independent predictor of restrictive motility, with a cutoff of 0.66 discriminating strabismus presence.

Conclusions:

• Quantitative 3D FMR is a clinically relevant biomarker in TED, reflecting muscle and fat involvement.
• Lower FMR identifies patients at higher risk for restrictive motility and strabismus.
• 3D FMR enhances risk stratification and longitudinal assessment in TED compared to 2D measurements.