Figure 8. Topography of retinal ganglion cell loss after light exposure. A and C: Photomontages of a representative control retina showing retinal ganglion cells (RGCs) identified by fluorogold (FG) tracing (A) or Brn3a immunodetection (C). B and D: Corresponding isodensity maps showing the spatial distribution of FG- or Brn3a-positive RGCs. These maps are filled contour plots generated by assigning a color code to each one of the subdivisions of each individual frame according to its RGC density value within a color-scale range that goes from 0 (purple) to 3,500 or higher (red) RGCs/mm². With both markers, it is observed that in control retinas, RGCs are densest in the dorsal pole, along the nasotemporal axis (A-D). E to L: Isodensity maps obtained from representative photoexposed retinas processed at increasing times ALE: 0 h (E), 1 month (F), 3 months (G), 6 months (H), 9 months (I, J generated from the same retina where RGCs were doubly identified by FG-tracing [I] and Brn3a detection [J]), and 12 months (K, L generated from the same retina where RGCs were doubly identified by FG-tracing (K) and Brn3a detection (L)). RGC loss is observed at 6 months ALE (H), as warm colors (red-oranges) are replaced by cooler ones (yellow-green-blues). At 9 (I, J) and 12 months (K, L) ALE, yellows and oranges have almost disappeared from the maps, indicating that RGC loss has gone further; this is observed to the same amount whether RGCs are identified by FG tracing (I, K) or Brn3a expression (J, L). The wedge-shaped areas of RGC loss have been marked with an X in K-L. The bottom of each map shows the number of RGCs counted in the retina wherefrom the map has been generated. The superior pole is at 12 o’clock. The scale bar represents 1 mm.