However, in 2013, a multiplex array analysis of tear fluids obtained from 18 PD patients compared to 17 healthy controls, which aimed to determine the TNF-α levels in tears and to explore the relationship between TNF-α and PD characteristics, discovered that the levels of TNF-α in PD patients were significantly higher than normal controls (p = 0.02) even though the level of TNF-α did not correlate with PD duration or severity [152]. The gene discussed is TNF; the disease is Parkinson disease.