information about people with dementia who have a sight impairement or who are blind

A good reference book on dementia is The Alzheimer's Action Plan by P. Murali Doraiswamy, Lisa P. Gwyther and Tina Adler.

In this book, the authors mention that vision loss can make people believe they have dementia. There is also a mention of a new eye test being developed to look for a type of cataract caused by amyloid plaque in the eye. Amyloid plaque is thought to cause Alzheimers.

You can search Google "dementia and vision impairment" to read articles  from the UK about this topic.