CXCR4 and Keratoconjunctivitis sicca: This study evaluated whether dry eye-associated ocular pain is associated with a modulation of the expression of the main endogenous opioid (enkephalin), CXCL12 and CCL2 chemokines, and their respective receptors CXCR4 and CCR2, respectively, as well as inflammatory markers (HLA-DR and IL-6) ex vivo in the ocular surface and in vitro in conjunctiva-derived epithelial cells.