A Pilot MRI Study of Upward Gaze-Induced Intraocular Pressure Elevation in Thyroid Eye Disease

Background/Objectives: To investigate the scleral inferior rectus–optic nerve distance (SIROND) and its association with intraocular pressure (IOP) elevation during upward gaze in patients with thyroid eye disease (TED), based on magnetic resonance imaging (MRI) examinations. Methods: This prospective study included 20 eyes (13 patients) diagnosed with active TED. All patients underwent orbital MRI in both primary and upward gaze positions before and 6 months after steroid pulse therapy. The SIROND was measured on MRI. IOP was recorded in both gazes. Changes in SIROND, inferior rectus (IR) muscle volume, proptosis, optic disc and scleral morphology, and IOP were analyzed pre- and post-treatment. Results: SIROND significantly decreased from primary gaze to upward gaze both before and after treatment (p < 0.001). Following steroid pulse therapy, there were significant reductions in IR muscle volume and proptosis (p < 0.05). Correspondingly, SIROND significantly increased in both primary and more in upward gaze post-treatment (p < 0.05). Although IOP during upward gaze was significantly higher than that in primary gaze both before and after treatment (p < 0.001), the gaze-related difference in IOP (p = 0.059), as well as SIROND, tended to be smaller after treatment (p < 0.001). A larger reduction in gaze-related pre-treatment SIROND was associated with greater IOP elevation in upward gaze (p = 0.038). MRI showed no evidence of globe compression by the IR muscle, and optic disc morphology remained unchanged following treatment. Conclusions: SIROND may serve as supportive radiological evidence for IOP elevation induced by upward gaze in patients with TED.