TNF and Parkinson disease: Although many neurological studies have relied on the biochemical analysis of CSF, the physiological sample of reference for CNS disorders, these biomarkers are also present in more accessible biological fluids, making sample acquisition less invasive, as exemplified for TNFα and OCBs that are present in higher amounts in tears of PD and MS patients, respectively (Devos et al., 2001; Çomoglu et al., 2013).