Change in ONL thickness with exposure to hyperoxia. Quantitative analysis of the impact of hyperoxia exposure (75% oxygen) to the photoreceptor population was performed in retinas of adult C57BL/6J mice (n = 12). (A) The average thickness of the outer nuclear layer (ONL) was sampled from four main areas; the inferior periphery, inferior central, superior central and superior periphery of the retinas from 0d control (black), 3d (red), 7d (blue), 10d (purple), and 14d (green). (B) Significant thinning of the ONL is evident by 10d of hyperoxic exposure, specifically in the inferior central area of the retina. At 14d in hyperoxia, depletion of the ONL has spread from the inferior central to the inferior periphery. The error bars representing the ± SEM. *Statistically significant thinning of the ONL (p < 0.05) compared to control animals.