Choroidal Medium-Large Vascular Index: A Novel OCTA Biomarker for Assessing Activity in Thyroid Eye Disease

Objectives: To elucidate the fundus changes between active and inactive thyroid eye disease (TED), as well as to establish reliable fundus indicators for assessing disease activity. Methods: In this retrospective cross-sectional study, 30 active TED patients (50 eyes), 26 inactive TED patients (47 eyes) and 26 healthy controls (50 eyes) were enrolled. All participants underwent macular optical coherence tomography (OCT) and angiography. Retinal thickness (RT), choroidal thickness (CT), retinal superficial vascular index (RSVI), retinal deep vascular index (RDVI), as well as choroidal capillary vascular index (CCVI) and choroidal medium-large vascular index (CMLVI) were automatically quantified. The diagnostic performance of these metrics for distinguishing active and inactive TED was evaluated through receiver operating characteristic (ROC) curve analysis. Results: The subfoveal and parafoveal CT was significantly greater in active TED group compared to both the inactive group and control group (P < 0.05). Among vascular indices, the CMLVI in both the subfoveal and parafoveal zone was significantly higher in active TED patients than in those with inactive disease or controls (P < 0.001). However, no significant differences were observed regarding RT, retinal vascular indices or the CCVI between active and inactive groups. ROC analysis indicated that CMLVI at subfoveal exhibited superior activity diagnostic efficacy (AUC = 0.811). Conclusions: Compared with inactive TED patients, active TED exhibit more prominent choroidal changes than retinal alterations. In addition, the variation in choroidal vessels is more significant than that in thickness. The subfoveal CMLVI is identified as an optimal, objective and reliable OCTA biomarker for assessing TED activity.