Can dementia affect the sight?

This definitely calls for a doctor appointment, but I'd also write down her exact words and keep track of the conditions under which this happens. Alzheimer's can affect how things are interpreted. Your mother's situation sounds different, but both an eye doctor and her Alzheimer's physician should know about this so that the cause - and potential treatment if one is available - can be determined.
Please update us when you can.
Carol

My husband was diagnosed with dementia, Alzheimers type almost 9 years ago. Last year he complained of feeling hair in his mouth and it was affecting his eating and resting. He spent a lot of time during the day gargling and spitting out his food.
He excellent doctor examined him and told me it was a result of his Alzheimers as often they become focused on something regarding their physical bodies. He said to give it a little time, don't comment on it, and it would probably go away.

Sure enough, it was in a matter of a couple weeks or less that he ceased to say anything about it. He has never mentioned it since.

Thanks to a knowledgable doctor for not performing a bunch of unnecessary tests. He checked him out thoroughly and made a wise determination that was right on.

It is good you are going in for an exam. If it isn't the eyes it may be a matter perception -- that is, how the brain takes in the signals from the eyes, rather than a physical problem with the eyes.

My husband had real problems with depth perception that came and went.

IMCO I think so. Your local Alzheimer's Association can provide a list of Alzheimer's and dementia specialists in your area.
primary care physicians don't always refer patients to specialists, even when it could help clarify a diagnosis or supplement primary treatment. In these cases, it’s up to you to sort through the maze of medical professionals.

Geriatric psychiatrists specialize in the mental and emotional needs of older individuals. They conduct thorough memory, mood, sleep, and thinking evaluations, and are particularly good at assessing memory problems associated with life stress, depression, anxiety, excess drinking, or family conflicts.

General neurologists and psychiatrists perform memory evaluations, but do not specialize in Alzheimer’s

My mom said a light bulb from the chandelier over the table exploded in her eye.
She was rattled when the bulb broke, but couldn't find the words to explain due to aphasia. The aide said she is fine, but I spent Saturday afternoon with her at Urgent Care having it checked.
The Dr did a thorough exam of her eyes and told us her eye
and cornea are normal. Mom loved the attention and all the fuss

My mom seen the eye Dr Friday she said yes it does affect the eyes

Old people can get dementia and also can develop cataracts. Unrelated. Just one more set of trips to doctor. Thankfully, cataract surgery is no biggie.

Yes, AD can affect sight. My husband died of an atypical young onset AD 10 years after diagnosis. HIs neurologist at Northwestern Medical Faculty Foundation diagnosed posterior cortical atrophy (PCA) which exhibits itself as a disruption of the occipital parietal visual pathway. There is much useful information about PCA at a closed Facebook Group "posterior cortical atrophy awareness" for which membership is required in order to limit the group to people with PCA, their family, friends, colleagues & medical practitioners.

My Ma has macular degeneration, so yes she is blind in one eye.. BUT was using blindness as a reason why she couldnt read. . Then one day it suddenly dawned on me that it wasnt that she couldnt see but her comprehension of the words was missing. I dropped the level of what I wrote down and did enlarge the print, and she was able to cope for a bit longer. I tried to use 4 letter words and left gaps in between, bullet point each point as such etc.Then followed up with phone calls like every 10 -15min if it was for her to heat her food., and to see that she had eaten it.
So all factors come into play, loss of vision, perception, comprehension, and memory.

My Mom had cataract surgery. When she complained about her glasses needing changing, I took her to the doctor. He said her eyes will never change nor will her glasses. It has to do with the Dementia. She has lost her vision on the sides and depth perception.