Effects of 670 nm light pretreatment on photoreceptor cell death following hyperoxia. Representative images of TUNEL-stained sections sampled from the inferior region of the NT and Tr retinas exposed to hyperoxia at different timepoints. TUNEL + labelling (red) was undetectable in the NT and Tr retinas from 0d (controls). A small population of TUNEL + photoreceptors was present in 3dNT retinas and continued to increase in number from 7, 10 and 14 days of exposure to hyperoxia. TUNEL + cells are also present in the 670 nm light-treated groups with significantly reduced number. The blue staining is Bisbenzimide, a DNA-specific stain, identifying the nuclear layers of the retina. Scale bar 25 μm.