Tear-Based Oxidative Stress Biomarkers in Primary and Sarcoidosis-Associated Dry Eye Disease

Dry eye disease (DED) has increasingly been linked to oxidative stress; however, the specific redox mechanisms underlying different clinical phenotypes remain incompletely understood. This study aimed to evaluate tear film oxidative stress profiles in patients with primary DED and sarcoidosis-associated DED (S-DED) by assessing lipid peroxidation, antioxidant enzyme activity, and total tear protein content, and to explore their relationship with clinical tear film dysfunction. Tear samples were analyzed for superoxide dismutase (SOD) and glutathione peroxidase (GPx) activities, as well as for malondialdehyde (MDA) and total protein levels, alongside standard clinical tests of tear film stability and secretion. Both DED groups exhibited significant oxidative alterations compared to controls, but with distinct redox signatures. Primary DED was characterized by markedly increased tear MDA levels, indicating predominant lipid peroxidation, whereas S-DED showed a more pronounced impairment of antioxidant defense, reflected by preserved or increased SOD activity in the context of significantly reduced GPx activity. Total tear protein levels were reduced in both groups, with evidence suggesting qualitative protein alterations in S-DED. The tear collection method significantly influenced the measured levels of several oxidative stress markers, underscoring the importance of sampling technique when interpreting tear-based redox profiles. Oxidative stress markers correlated with clinical measures of tear film dysfunction, supporting their physiological relevance. These findings demonstrate that DED encompasses heterogeneous oxidative stress mechanisms and that sarcoidosis acts as a modifier of ocular surface redox homeostasis. Distinct tear-based redox profiles differentiate primary from sarcoidosis-associated dry eye, highlighting the potential value of oxidative biomarkers for phenotyping DED beyond tear deficiency alone.