FAS and age-related macular degeneration: Early studies showed that photoreceptor and RPE cells in AMD eyes stained positive for DNA fragmentation (i.e., were positive for terminal deoxynucleotidyl transferase dUTP nick end labeling—TUNEL), suggesting activation of the apoptotic cell death pathway and also that the Fas/FasL pathway was the upstream regulator of apoptosis in AMD eyes [24].