Visual field and orbital computed tomography correlation in dysthyroid optic neuropathy due to thyroid eye disease

Purpose: The pathogenesis of dysthyroid optic neuropathy (DON) in thyroid eye disease (TED) is thought to be compression of the apical optic nerve by hypertrophied extraocular muscles. We correlated worsening DON to the area occupied by extraocular muscles. Methods: Records of adults with TED DON evaluated from 1/1/2013 to 1/1/2018 were retrospectively reviewed. Each patient's visual field with the worst mean deviation (MD) was selected. Orbit CT scans were reviewed. Reformatted oblique coronal images were created perpendicular to the optic nerve. The cross-sectional area (CSA) of the orbit and each muscle group was measured and expressed as ratios of the CSA of the orbital apex. Univariate and multivariate analysis was performed for predictors of HVF MD. Results: 34 orbits with TED DON were analyzed. On orbital CT, the superior muscle complex occupied 15% of the apex (range 6-26%), inferior 18% (range 6-33%), lateral 10% (range 4-18%), medial 17% (range 8-27%), and all combined 61% (range 28-80%). Increasing total muscle area and superior complex area correlated with worsening MD. In multivariate linear regression, the superior muscle complex remained a significant predictor of MD (p = 0.01) over total muscle area (p = 0.25). Conclusions: Enlargement of extraocular muscles is common in TED, but DON occurs in only 6%. Our findings demonstrate that as DON worsens, as quantified by visual field MD, the superior muscle complex crowds the apex. This is consistent with the typical inferior visual field findings seen in TED DON. Hypertrophy of the superior rectus and levator palpabrae superioris complex may be predictive of worsening DON.