Criteria for dissection quality were applied before proceeding. Any retina that was appreciably torn in such a way as to mimic the appearance of a reliving cut, or any retina that exhibited significant tissue loss or damage of the central or mid-central retina was discarded. To observe the s-opsin gradient, dissected retinas (Figure 1d – left and middle panel) were mounted on nitrocellulose membrane paper and immunohistochemistry was conducted similarly to Sondereker et al. (2017) (link). Retinas were fixed in 4% paraformaldehyde for 40 minutes and then rinsed (3 × 15 minutes) in 0.1M phosphate-buffered saline (PBS). Retinas were placed in blocking solution and incubated at 4° C overnight. Retinas were then incubated at 4° C in blocking solution for six days with primary antibody goat anti-s-opsin (Santa Cruz Biotechnologies, Cat# sc14363, RRID: AB_2158332). The retinas were washed (6 × 10 minutes) in 0.1M PBS and placed in blocking solution overnight at 4° C with secondary antibody donkey anti-goat Alexa Fluor 594 (Life Technologies, Cat# A11058, RRID: AB_2534105). Retinas were rinsed (6 × 10 minutes) in 0.1M PBS before being mounted on a on a glass slide with Aquamount and covered with a 1.5 μm thick coverslip.