We subsequently used the mouse ON crush model to screen multiple tumor suppressor genes and discovered that deletion of phosphatase and tensin homolog (PTEN), but not Rb (retinoblastoma), P53, Smad4, or LKB1 (liver kinase B1), promotes significant ON regeneration and RGC survival (Park et al., 2008). This evidence concerns the gene PTEN and retinoblastoma.