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  • Updated 10.21.2020
  • Released 04.20.2013
  • Expires For CME 10.21.2023

Visual hallucinations in blindness

Introduction

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) most commonly refers 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) (10; 08; Esperjesi and Akbarali 2004; 53; 44).

Charles Bonnet (1720-1793)
Engraving by Danish printmaker Johan Frederik Clemens (1749-1831) from a 1777 painting by Danish painter Jens Juel (1745-1802).

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 (25; 32). 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 (26).

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) (37; 99; 117; 116; 100; 07; 69; 75; 32; 18; 72; Esperjesi and Akbarali 2004; 53; 125; 19; 81). Other definitions are also employed, however, which leads to confusion and confounds clarification of the pathophysiology of the disorder (85; 39): indeed, because of the varying definitions, a number of authors have argued that the eponym is no longer useful [eg, (89; 15)]. For example, some authors accept as Bonnet hallucinations cases with unformed visual hallucinations (photopsias) (15; 125; 01; 59), cases with dementia or other cognitive impairment (120), or cases with epileptic visual hallucinations (80; 13), whereas others restrict cases to elderly patients, to patients with complex formed visual hallucinations, or to cases with prechiasmal visual impairment (21; 32; 118).

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