In one of the earliest studies [18], expression of COL1A1, COL1A2, COL3A1, COL4A1, COL6A3, COL15A1, FN1, POSTN and SPARC was increased in primary pterygium; however, these genes were uniformly downregulated in recurrent pterygium [18]. This evidence concerns the gene COL4A1 and pterygium.