This is an interesting study in PLoS One examining the involvement of melatonin in the retina, particularly in the survival of retinal neurons through aging studies in CH3-f+/+ mice, a melatonin proficient mouse strain. As expected, certain physiological measures (a and b waves) are lost during aging, and in particular, the daily circadian rhythms of those measures. However, the authors, Kenkichi Baba, Francesca Mazzoni, Sharon Owino, Susana Contreras-Alcantara, Enrica Strettoi and Gianluca Tosini did something really interesting and added exogenous melatonin to their assay and concluded that responsiveness of exogenous melatonin is also reduced during aging.