A team from University School of Medicine in St Louis, Missouri found that the patients who had high levels of the amyloid or tau proteins had also significant thinning devoid of blood vessels in the center of their retina that is responsible for our most precise vision.

http://www.dailymail.co.uk/health/article-6090749/Eye-exam-spot-risk-Alzheimers-disease-long-symptoms-arise.html