One of the earliest signs of Alzheimer's Disease even before any noticeable change in memory is blurred vision, since the eye or "Retina" back of the eye is actually brain tissue. Swelling of the layers of the retina or forming cystic changes as in diabetic retinopathy is a very early sign supported by many scientific articles in the literature.
Predident Ronald Reagan had to wear glasses, mainly due to burry vision. Retinal edema (swelling of the layers of the retina) he was very fond of jelly bellies.