One week after the viral injections, the mice were humanely killed, and the eyes were removed and fixed with 4% paraformaldehyde in phosphate-buffered saline solution (PBS) for 1 hour. The eyes were then transferred to 0.4% paraformaldehyde overnight. To make flat mounts, the cornea and crystalline lens were removed, and the entire retina was carefully dissected from the eyecup. Four radial cuts were made from the edge to the equator of the retina to make it flat. After 3 washes in PBS, retinas were permeablized with 0.5% Triton X-100 (Dow Chemical Corporation, Midland, Michigan) in PBS for 1 hour followed by incubation with a blocking solution of the 0.5% Triton X-100 and 10% goat serum for 1 hour. The flat-mounted retinas were then rinsed in PBS and incubated with a mixture of mouse monoclonal anti-FLAG M2 antibodies conjugated to Cy3 (1:100) (Sigma-Aldrich Corp, St Louis, Missouri) or polyclonal rabbit anti-GFP antibodies (1:400) (Abcam, Cambridge, Massachusetts) along with monoclonal rat Thy1.2 (1:200) (Abcam) overnight at 4°C. Primary antibody solution was contained in 10% goat serum and 0.2% Triton X-100 in PBS (pH, 7.4). After 3 washes with PBS, the retinas were treated with the secondary antibody, goat anti-rabbit Cy2 (Jackson Immunoresearch Laboratories, Inc, West Grove, Pennsylvania), goat antimouse Cy2 (Jackson Immunoresearch Laboratories, Inc), goat antimouse Cy3 (Jackson Immunoresearch Laboratories, Inc), or goat antimouse IgG (Alexa Fluor 488; Invitrogen, San Diego, California) and 4",6-diamidino-2-phenylindole (2μg/mL) (Santa Cruz Biotechnology, Inc, Santa Cruz, California), in 1:500 dilution contained in 10% goat serum and 0.2% Triton X-100 and incubated at 4°C overnight. The retinal tissues were finally washed 3 times in PBS. The whole mounts were then placed on a glass slide (RGC layer facing up), coverslipped, and observed for fluorescence with a confocal microscope (Leica TCS SP5; Leica, Wetzlar, Germany). For cryosections, the retinas were incubated overnight in 30% sucrose and then embedded in optimal cutting temperature embedding compound (Sakura Finetek, Torrance, California). Retinal sections, 8 μm in thickness, were then mounted with fluorescent mounting medium (Vectashield; Vector Laboratories, Burlingame, California) and examined for fluorescence using the confocal microscope.