Light Discomfort Thresholds in Patients with Moderate-to-Severe Active versus Mild Non-Active Thyroid Eye Disease

Purpose: To quantitatively assess light sensitivity thresholds and ocular surface parameters in patients with thyroid eye disease (TED) compared to sex- and age-matched patients with dry eye disease (DED) and healthy controls, and to further investigate differences between moderate-to-severe active and mild non-active TED. Patients and Methods: This cross-sectional, controlled study included patients with TED, patients with DED, and healthy controls. Light sensitivity was evaluated using the Lumiz 100 device (Essilor International, Paris, France) under three lighting conditions: continuous warm, continuous cold and flashing warm. TED patients were further stratified into moderate-to-severe active and mild non-active subgroups. In addition, ocular surface parameters were assessed using the Keratograph 5M (Oculus, Wetzlar, Germany). Correlations between light sensitivity thresholds and clinical parameters were analyzed. Results: Out of 93 included patients, 39 had TED (14 moderate-to-severe active, 25 mild non-active), 25 had DED, and 29 were healthy controls. TED patients demonstrated significantly lower total light sensitivity thresholds compared to healthy controls (3.17 ± 0.52 vs 3.47 ± 0.42 log10[lux], p = 0.040) but higher thresholds compared to DED patients (2.71 ± 0.52 log10[lux], p = 0.003). Among TED patients, those with moderate-to-severe active disease exhibited significantly lower light sensitivity thresholds than those with mild non-active disease (2.85 ± 0.48 vs 3.35 ± 0.47 log10[lux], p = 0.004). A significant negative correlation was found between total light sensitivity threshold and ocular discomfort symptoms in both subgroups of TED patients (r =-0.623, p = 0.017 for moderate-to-severe active TED and r = -0.405, p = 0.045 for mild non-active TED, respectively). Conversely, no significant correlation was found between light thresholds and tear film or thyroid function parameters. Conclusion: Light sensitivity represents a significant and quantifiable manifestation of TED, particularly in patients with active disease. Quantitative assessment of light sensitivity might be incorporated into clinical evaluation of TED patients to better characterize disease burden and guide management strategies.