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While visual hallucinations can be a symptom of mental illness, there are also a number of nonpsychiatric causes of "seeing things."
A common type of visual hallucination occurs after a stroke or other type of brain injury.
If the temporal lobe (the part of the brain that controls memory) is injured, people may experience visual hallucinations along with the sensation of a strange odor.
If there is an injury to the occipital lobe (the part of the brain that controls vision), there may be visual hallucinations without any odor sensations.
The exact cause of these types of hallucinations is unknown.
Vision loss from an eye injury or an eye disease, such as macular degeneration, also may sometimes lead to hallucinations -- a situation called Charles Bonnet syndrome.
In this syndrome, patients see visual hallucinations in areas of their visual field in which they are missing vision.
The hallucinations may be of faces or objects, as well as of abstract images such as light patterns.
Because these hallucinations occur in areas of missing vision, one way to make the hallucinations vanish is for patients to "redirect" their gaze to parts of the visual field where they can see.
Your mother should certainly have a neurologic workup.
Although visual hallucinations can occur in the absence of neurologic problems, there is no way to know whether she may have suffered small strokes without an imaging study (MRI).
You may also want to consult directly with your mother's eye doctor and neurologist to assist in her care.
Best Wishes to you and your mother,