TGFB2 and posterior polymorphous corneal dystrophy: The mean levels of active TGF-β2 (mean ± SD) in the AH of the PPCD older specimens (collected between 1994 and 2002) and younger specimens (collected between 2003 and 2008) were 368.12 ± 124.62 pg/ml and 407.18 ± 104.16 pg/ml, respectively.