CASP1 and pterygium: However, as demonstrated in our study, it is surprising that both of IL-18 and IL-1β were aberrantly expressed concurrently after the NLRP3/Caspase-1 pathway was activated in pterygium (Figure 2), suggesting that IL-18 may not negatively regulate the expression of IL-1β when pterygium is present; however, the specific mechanism needs further study.