MBTPS1 and pterygium: The relative mRNA expressions of S1P2 (p < 0.05), S1P4 (p < 0.01), and S1P5 (p < 0.05) were significantly higher in pterygium tissues than in normal conjunctiva tissue (Figure 1), suggesting the involvement of S1P activation, along with the S1P receptors mentioned above, in the genesis of pterygium.