Long-term dry eye is associated with increased expression of inflammatory factors, such as tumor necrosis factor-alpha (TNF-α), matrix metalloproteinase (MMP-2, MMP-9), intercellular adhesion molecule-1 (ICAM-1), and vascular cell adhesion molecule-1 (VCAM-1) in the ocular surface7,8,14–16. The gene discussed is MMP9; the disease is Keratoconjunctivitis sicca.