CXCR4 and pterygium: Bamdad et al. (2017) reported that upregulation of SDF-1 contributes to pterygium (Bamdad et al., 2017). Kim et al. (2013) reported that the levels of CXCL12 and CXCR4 can be used to determine the severity of pterygium (Kim et al., 2013). GADD34 is a growth cycle protein that could be induced by growth arrest, DNA damage, and other kinds of cell stress. When intracellular proteins cannot fold properly, the disruption of endoplasmic reticulum (ER) physiological function leads to ‘endoplasmic reticulum stress’. A long period of ER stress can induce the expression of GADD34 (Reid et al., 2016).