Can dementia cause hallucinations or visual disturbances?

It can happen: The most common type of dementia is alzheimer's -- patients in later stages can have auditory/visual hallucinations. These may predict a more rapid decline of cognitive function. In lewy-body dementia (2nd most common type), 80% of patients have visual hallucinations. Patients with new onset of hallucinations need urgent medical evaluation to find and treat reversible causes of delirium.

Not exactly: Hallucinations or visual disturbances aren't symptoms of dementia, per se. However, patients with dementia may experience hallucinations or delusions if a delirium or other cause of these symptoms is superimposed on the dementia. Delirium develops over a short period of time (usually hours to days) and tends to fluctuate throughout the day. Patients with delirium often respond well to treatment.