Lack of treatment for a condition is not the best proof for the nonexistence of the condition. In the case of Age-Related Macular Degeneration (AMD), the findings of lack of treatment more likely "indicate poor access to AMD treatment."
Moreover, just this week a seminal study concluded that the retina -- that direct extension of our brain -- loses thickness as the Alzheimer's disease sets in. The connection is so direct that some folks are now scrambling to make an apparatus to measure retinal thickness -- for diagnosing and tracking the progression of Alzheimer's.
No, Dr. Keenan, "people with dementia and blindness may [NOT] be extremely isolated." And "dementia may [NOT] mask visual loss and lead to inaction." Rather, the visual loss itself, the glaucoma, is the proof of the advancing dementia. See http://www.bbc.co.uk/news/health-24924488