Visual hallucinations in blindness

Douglas J Lanska MD FAAN MS MSPH (Dr. Lanska of the Great Lakes VA Healthcare System and the University of Wisconsin School of Medicine and Public Health has no relevant financial relationships to disclose.)
Originally released April 20, 2013; last updated February 7, 2017; expires February 7, 2020

This article includes discussion of visual hallucinations in blindness, Charles Bonnet syndrome, Bonnet syndrome, Bonnet hallucinations, and Charles Bonnet plus syndrome. The foregoing terms may include synonyms, similar disorders, variations in usage, and abbreviations.

Overview

In this article, the author explains the clinical presentation, pathophysiology, diagnostic workup, and management of visual hallucinations in blindness. Bonnet syndrome (sometimes referred to as Charles Bonnet syndrome) is now most commonly considered to refer to visual hallucinations in visually impaired individuals with full alertness, unimpaired cognition, and no psychosis. Although Bonnet syndrome is most commonly identified in patients with bilaterally decreased central visual acuity, similar phenomena also occur in patients with retrochiasmal visual field defects. Bonnet hallucinations are thought to result from a "release" mechanism associated with modality-specific sensory deprivation, ie, "phantom vision" akin to phantom limbs in patients with loss of somatosensory input after an amputation. Although there is no definitive treatment available for Bonnet syndrome, various ophthalmologic interventions, behavioral strategies, and pharmacologic agents have been used to try to reduce or relieve symptoms.

Key points

 

• Bonnet syndrome (sometimes referred to as Charles Bonnet syndrome) is now most commonly considered to refer to visual hallucinations in visually impaired individuals with full alertness, unimpaired cognition, and no psychosis.

 

• These hallucinations can include simple or complex hallucinations, including geometric shapes, animals ("zoopsias"), human figures, buildings, or landscape scenes.

 

• Bonnet hallucinations are usually well-defined and clear, often elaborate, visual hallucinations restricted to a single modality, ie, visual hallucinations only without associated olfactory, gustatory, auditory, or tactile hallucinations.

 

• Patients generally have full or partial retention of insight, without delusions or psychosis, and without associated intoxication or withdrawal.

 

• Bonnet syndrome frequently goes unrecognized in clinical practice due to lack of awareness among providers and to patients' reluctance to report hallucinatory experiences. Many elderly patients with such hallucinations are concerned that these indicate mental illness or the incipient development of dementia.

 

• Although Bonnet syndrome is most commonly identified in patients with bilaterally decreased central visual acuity, similar phenomena also occur in patients with retrochiasmal visual field defects.

 

• Bonnet hallucinations are thought to result from a "release" mechanism associated with modality-specific sensory deprivation, ie, "phantom vision" akin to phantom limbs in patients with loss of somatosensory input after an amputation.

 

• Although there is no definitive treatment available for Bonnet syndrome, various ophthalmologic interventions, behavioral strategies, and pharmacologic agents have been used to try to reduce or relieve symptoms.

Historical note and terminology

In the late 18th century, Charles Bonnet reported visual hallucinations in elderly persons who were cognitively normal (ie, in Bonnet's 89-year-old grandfather Charles Lullin and, later, in Bonnet himself) (Bonnet 1769; Berrios and Brook 1982; Esperjesi and Akbarali 2004; Jacob et al 2004; Hedges 2007).

Image: Charles Bonnet (1720-1793)
In 1936, de Morsier eponymously recognized Bonnet's report and designated Bonnet syndrome as a syndrome of visual hallucinations in elderly persons with ocular lesions and intact cognition (de Morsier 1936; ffytche and Howard 1999). Three decades later, de Morsier tried to remove ocular disease from the syndromic definition and considered Bonnet hallucinations as visual hallucinations occurring among the elderly with intact cognition, regardless of etiology (de Morsier 1967).

Bonnet syndrome (sometimes referred to as Charles Bonnet syndrome) is now most commonly considered to refer to visual hallucinations in visually impaired individuals with full alertness, unimpaired cognition, and no psychosis (and this is the operational definition used for this article) (Gold and Rabins 1989; Schultz and Melzack 1993; Teunisse et al 1994; Teunisse et al 1995; Schultz et al 1996; Batra et al 1997; Manford and Andermann 1998; Nadarajah 1998; ffytche and Howard 1999; Chen et al 2001; Menon et al 2003; Esperjesi and Akbarali 2004; Jacob et al 2004; Wilkinson 2004; Choi et al 2005; Pang 2016). Other definitions are also employed, however, which leads to confusion and confounds clarification of the pathophysiology of the disorder (Plummer et al 2007): indeed, because of the varying definitions, a number of authors have argued that the eponym is no longer useful [eg, (Rao 1997; Burke 2002)]. For example, some authors accept as Bonnet hallucinations cases with unformed visual hallucinations (photopsias) (Burke 2002; Wilkinson 2004; Abbott et al 2007; Khan et al 2008), cases with dementia or other cognitive impairment (Ukai et al 2004), or cases with epileptic visual hallucinations (Ossola et al 2010; Brown-Vargas and Cienki 2012), whereas others restrict cases to elderly patients, to patients with complex formed visual hallucinations, or to cases with prechiasmal visual impairment (Cole 1992; ffytche and Howard 1999; Tomsak et al 2003).

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