MUC5AC and Keratoconjunctivitis sicca: Previous studies have shown that some inflammatory cytokines in tears, such as IL-1β, IL-6, IL-8, and IL-13, are elevated in TAO patients compared with healthy patients (Kishazi et al., 2018; Ujhelyi et al., 2012) [20,21]; these inflammatory cytokines are released through external stimuli and then activate MAPK intracellular signalling pathways, resulting in apoptosis, goblet cell loss, and mucin disturbance on the ocular surface to deteriorate dry eye status (Chen, 2019; Ujhelyi et al., 2012) [33,34].