One such factor is ciliary neurotrophic factor (CNTF), where non-viral delivery alleviated photoreceptor loss in the rd1, nervous (nr/nr) and RhoQ344ter mouse models of retinal degeneration (LaVail et al., 1998), Rdy feline model of retinal atrophy (Chong et al., 1999), and rcd1 canine model of retinitis pigmentosa (RP) (Tao et al., 2002). This evidence concerns the gene PDE6B and retinal degeneration.