For instance, commercially viable use of qualitative analysis of matrix metalloproteinase‐9 (MMP‐9) in tears for the diagnosis of dry eye,[7] and diabetes could be diagnosed by quantitative detection of glucose in tears as well.[8] Moreover, compared with the blood, the compositions in tears are simpler and have less interference from other substances during the detection progress. The gene discussed is MMP9; the disease is Keratoconjunctivitis sicca.