Eyeball descending identification using MRI-based spatial coordinates in thyroid-associated orbitopathy patients with unilateral upper eyelid retraction.

Background: Upper eyelid retraction (UER), the primary symptom of thyroid-associated orbitopathy (TAO), can affect perceived eyeball position. This study aimed to assess relative anatomical positions, and examine changes in eyeball position and related factors in TAO patients with unilateral UER.

Methods: In total, 30 TAO patients with unilateral UER and 67 healthy control participants were included in this retrospective study. Using orbital magnetic resonance images, image processing techniques were employed to measure the difference between the vertical distance of the eyeballs for each patient and each healthy control participant. The thickness of the levator palpebrae superioris (LPS), superior rectus (SR), and inferior rectus (IR) muscles, and the volume of the LPS-SR complex were measured in the patient cohort.

Results: In the healthy control group, the vertical distance difference between the eyeballs was -0.067±0.938 mm (P=0.560). In the patient group, the descent distance difference was 1.192±1.159 mm (P<0.001). The increase in the thickness of the LPS muscle was greater in the patients with a descent difference (n=25) than those without a descent difference (n=5; P<0.001). The descent distance in the impaired eyes was positively correlated with an increased thickness of the LPS muscle (P<0.001). No significant correlations were observed between the descent distance and the increased thickness of the SR muscle, the increased thickness of the IR muscle, or the volume of the LPS-SR complex.

Conclusions: In TAO patients with unilateral UER, the eyeball of the affected side had a descent difference, which was associated with a thickening of the LPS muscle.