He’s been making new ‘friends’

Symptoms
There are no specific diagnostic criteria for Charles Bonnet syndrome (Table 2). However, the following are generally accepted for diagnosis⁹:
   • grossly intact cognition, although mild cognitive impairment may be present in some cases¹⁰
    • underlying visual disorder, usually acquired, such as glaucoma, age-related macular degeneration, diabetic retinopathy, central retinal artery occlusion, and optic neuritis^3,4,11
   • no hallucinations or perceptive difficul­ties in other sensory modalities
   • generally intact insight
   • absence of delusions
   • absence of other neurologic, psychiat­ric, toxic, or metabolic conditions; medical causes of delirium must be ruled out.

Hallucinations might not be disturb­ing to the patient. Hallucinations could be simple (light flashes, lines, or geomet­ric shapes) or complex (faces, figures, or scenes),¹² and perceived as in color or in black and white. Hallucinations mostly are pleasant and rarely have any emotional impact or meaning. Although hallucina­tions are almost exclusively visual, they can be accompanied by noise or auditory hallucinations.^13,14

Other characteristics of Charles Bonnet syndrome include:  
   • typical age of onset is approximately 72 years (range, 70 to 92 years)  
   • no sex distinction has been identified  
   • episodes can last from a few seconds to few hours; the syndrome may last a few days or a few years⁵     
   • it is not uncommon for episodes to occur in clusters, followed by symptom-free intervals and recurrences  
   • symptoms tend to fade away as patients progress to complete loss of sight.¹⁵

The course of Charles Bonnet syndrome is uncertain and unpredictable and the epi­sodic nature can be frustrating for both patient and clinician. The syndrome could be misdiagnosed as a psychiatric condition.

Pathophysiology
The precise mechanism behind simple or complex vivid hallucinations in persons with Charles Bonnet syndrome is unclear. Several theories have been proposed.

Release theory proposes a loss of input to the primary visual areas, which decreases cortical inhibition and further causes disin­hibition of visual association areas, thereby “releasing” visual hallucinations.¹⁶ Research suggests that this might be an attempt by surviving neurons to recover vision. Loss of input somehow causes surviving neurons to adapt by increased sensitivity to residual visual stimuli.

Deafferentation theory. This relatively new theory proposes deafferentation of the visual sensory pathway, which, in turn, causes disinhibition of neurons in the visual cortical regions, thereby caus­ing them to fire spontaneously. This could cause a sensation analogous to phantom limb pain, which would be called “phan­tom vision presence of brain activity in the absence of an actual visual input.” Further, biochemical and molecular changes have been proposed to explain the deafferenta­tion theory.¹⁷

Neurobiological evidence. Limited data are available for a neurobiological basis to visual hallucinations in Charles Bonnet syndrome. A few studies have used func­tional MRI and single-photon emission CT and reported possible association of visual hallucinations to specific visual areas.^18,19

Risk factors
Social or physical isolation, loneliness, low extraversion, and shyness are risk factors for Charles Bonnet syndrome in visually impaired people.²⁰ Sensory deprivation and low level of arousal favor the occur­rence of hallucinations.⁵ Rate of vision loss—not the nature of pathology or sever­ity of visual impairment—has been sug­gested to increase the risk of developing Charles Bonnet syndrome.²¹

What are the treatment options for Charles Bonnet syndrome?
   a) begin an antipsychotic
   b) do nothing; there is no cure
   c) educate the patient about the nature of the hallucinations
   d) refer the patient to an ophthalmologist for evaluation of vision loss

Treatment
There are several modalities to manage visual hallucinations in a patient with Charles Bonnet syndrome (Table 3). After ruling out medical and other psychiat­ric causes of visual hallucinations, treat­ment might not be indicated if the patient is not disturbed by the hallucinations. In most cases, reassurance and educating the patient and family about the benign nature of the visual hallucinations is all that is needed.

For patients who are disturbed by these visions or for whom there is a treatable cause, treatment could include cataract removal, medical therapy to reduce intra­ocular pressure in glaucoma, treatment of diabetic retinopathy, or laser photoco­agulation. These treatments are associ­ated with a reduction in hallucinations.²²

In some cases, hallucinations disappear as visual acuity deteriorates. Psychotropics have been used to treat Charles Bonnet syndrome, including:
   • antipsychotics, including haloperi­dol, risperidone, and olanzapine
   • anticonvulsants, including valproic acid, gabapentin, and carbamazepine
   • antidepressants, including mirtazap­ine and venlafaxine.^23-30

Some experts recommend a conserva­tive approach, which might be justified because some cases of Charles Bonnet syndrome are episodic and remit sponta­neously.³¹ Again, however, consider phar­macotherapy if a patient is disturbed by hallucinations or if hallucinations impair overall functioning.