It has been reported since the early part of the 20th century that people with Visual Impairments often see things that are not there. These are not the hallucinations of mental illness but seem to arise because the visual centres of the brain dislike the disjointed, fuzzy blank areas that exist in the visual field of partial sighted or visually impaired people.The Mind wants to see shapes/images it can recognise and process so it projects (or possibly recalls) images onto the real world.
CBS hallucinations do not last long, usually a shake of the head or turning a light on or off will dispel them. So long as the person seeing the hallucination knows they are not real then they should be reassured that this is not the onset of some type of dementia.
The following poem, which was apparently written about a ghost epitomises to me what it must be like to have a CBS hallucinations:
Yesterday, upon the stair
I met a man who wasn’t there
He wasn’t there again today
I wish, I wish he’d go away..read what's missing
Medical science has no proven treatments for CBS, but keeping the mind active and socialising as much as possible do seem to help the sufferer keep control of the hallucinations. However If they are causing severe distress then there are some medications that your GP might consider trying.