Objectives. A review of the literature on unreal visual perceptions (visual hallucinations and parahallucinations - VHP).
Review. Unreal visual perceptions are qualified as hallucinations irrespective of the amount of accompanying insight. Many states are reported in the course of which hallucinations may occur. First of all, there is a variety of brain diseases, in particular vascular and degenerative conditions, besides, eye diseases, psychiatric disorders, and adverse side effects of medicaments. Much attention is still paid to the Charles Bonnet syndrome. It is difficult to estimate the real prevalence of VHP, because patients are reluctant to reveal such experiences. Impaired vision and old age are considered to be the main risk factors for VHP. Content of VHP is not specific to any definite disorder. Treatment of VHP is regarded as difficult.
Conclusion. The span of VHP prevalence indices is considerable. No single riskfactor is either necessary or sufficient for the VHP onset. There are no qualitative differences in the VHP clinical picture related to the type of concurrent disorders. If VHP are correctly diagnosed, the treatment outcome is good. An analysis of collected VHP cases will be presented in the second part of this paper.