APP and Alzheimer disease: Collectively, in AD animal mice, we observed that (1) Aβ(1–42) monomers infused into CSF in the ICV region acutely transport to the blood and the aqueous humor, (2) artificially injected Aβ(1–42) levels in CSF are proportionally reflected in the aqueous humor in mice without human APP expression, and (3) the progressive decrease of Aβ(1–42) levels in representative fluid biomarkers, CSF and blood, is not observed in aqueous humor.