In conclusion, although the question of whether the AD-like pathological alterations begin in the retina earlier than in the brain [15,41], or whether these alterations occur concomitantly [42] is still open to debate, it is currently clear that, at least in the APP/PS1 model where the pre-symptomatic stage (in contrast to humans) can be investigated, the brain and retinal pathologies are well correlated [43]. This evidence concerns the gene APP and Alzheimer disease.