Content and associated signs/symptoms. The visual hallucinations of patients with Charles Bonnet syndrome appear almost exclusively in the defective visual field. Images tend to be complex, colored, with moving parts, and appear in front of the patient. The hallucinations are usually of familiar or normal-appearing people or mundane objects, and as such, the patient often does not realize the hallucinated entity is not real. In patients without comorbid psychiatric disease, visual hallucinations are not accompanied by any other types of hallucinations. The most commonly hallucinated entities are people, followed by simple visual hallucinations of geometric patterns, and then by faces (natural or cartoon-like) and inanimate objects. Hallucinations most commonly occur daily or weekly, and upon waking. These hallucinations most often last several minutes, though they can last just a few seconds or for hours. Hallucinations are usually emotionally neutral, but most patients report feeling confused by their appearance and having a fear of underlying psychiatric disease. They often gain insight to the unreal nature of the hallucinations after counseling.48
Visual hallucinations at the sleep/wake interface
Hypnagogic and hypnopompic hallucinations are fleeting perceptual experiences that occur while an individual is falling asleep or waking, respectively.49 Because by definition visual hallucinations occur while the individual is fully awake, categorizing hallucination-like experiences such as hypnagogia and hypnopompia is difficult, especially since these are similar to other states in which alterations in perception are expected (namely a dream state). They are commonly associated with sleep disorders such as narcolepsy, cataplexy, and sleep paralysis.50,51 In a study of 13,057 individuals in the general population, Ohayon et al4 found the overall prevalence of hypnagogic or hypnopompic hallucinations was 24.8% (5.3% visual) and 6.6% (1.5% visual), respectively. Approximately one-third of participants reported having experienced ≥1 hallucinatory experience in their lifetime, regardless of being asleep or awake.4 There was a higher prevalence of hypnagogic/hypnopompic experiences among those who also reported daytime hallucinations or other psychotic features.
Content and associated signs/symptoms. Unfortunately, because of the frequent co-occurrence of sleep disorders and psychiatric conditions, as well as the general paucity of research, it is difficult to characterize the visual phenomenology of hypnagogic/hypnopompic hallucinations. Some evidence suggests the nature of the perception of the objects hallucinated is substantially impacted by the presence of preexisting psychotic symptoms. Insight into the reality of these hallucinations also depends upon the presence of comorbid psychiatric disease. Hypnagogic/hypnopompic hallucinations are often described as complex, colorful, vivid, and dream-like, as if the patient was in a “half sleep” state.52 They are usually described as highly detailed events involving people and/or animals, though they may be grotesque in nature. Perceived entities are often described as undergoing a transformation or being mobile in their environment. Rarely do these perceptions invoke emotion or change the patient’s beliefs. Hypnagogia/hypnopompia also often have an auditory or haptic component to them. Visual phenomena can either appear to take place within an alternative background environment or appear superimposed on the patient’s actual physical environment.
How to determine the cause
In many of the studies cited in this review, the participants had a considerable amount of psychiatric comorbidity, which makes it difficult to discriminate between pure neurologic and pure psychiatric causes of hallucinations. Though the visual content of the hallucinations (people, objects, shapes, lights) can help clinicians broadly differentiate causes, many other characteristics of both the hallucinations and the patient can help determine the cause (Table3,4,12-39,41-52). The most useful characteristics for discerning the etiology of an individual’s visual hallucinations are the patient’s age, the visual field in which the hallucination occurs, and the complexity/simplicity of the hallucination.
Patient age. Hallucinations associated with primary psychosis decrease with age. The average age of onset of migraine with aura is 21. Occipital lobe seizures occur in early childhood to age 40, but most commonly occur in the second decade.32,36 No trend in age can be reliably determined in individuals who experience hypnagogia/hypnopompia. In contrast, other potential causes of visual hallucinations, such as delirium, neurodegenerative disease, eye disease, and peduncular hallucinosis, are more commonly associated with advanced age.
Continue to: The visual field(s)