GUCY2D and Leber congenital amaurosis: While there is general consensus that LCA1 is associated with severely attenuated or ablated ERG (Perrault et al., 1999b, 2000; Hanein et al., 2004; Yzer et al., 2006; den Hollander et al., 2008), reports on the extent of photoreceptor degeneration associated with this form of LCA have been conflicting (Milam et al., 2003; Porto et al., 2003; Simonelli et al., 2007; Pasadhika et al., 2010).