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Although there were no universally approved diagnostic criteria for this syndrome, psychosis, impaired sensorium, dementia, intoxication, metabolic derangement and focal neurological illness must first be excluded[6]. The following diagnostic criteria[7] are accepted by most authorities: the presence of formed, complex, persistent or repetitive, stereotypical visual hallucinations; and full or partial retention of insight into the unreal nature of the hallucinations; and absence of hallucinations in other sensory modalities; and absence of primary or secondary delusions.
Patients with this syndrome often described varied visual hallucinations of figures, human or animals which present in variable sizes. These complex hallucinations are always outside the body and may last from a few seconds to most of the day. It was observed that these hallucinations usually do not bear any personal meaning and the patients can voluntarily make the image disappear by closing their eyes[2,3].
The pathogenesis is unclear although sensory deprivation and the reaction of the visual cortex to the sudden or progressive lack of visual stimulation which results in release phenomenon had been implicated (deafferentation hypothesis)[810]. Other authors further postulated that the dynamic decrease in visual acuity bears a greater impact than in chronic condition of low visual acuity in the development of Charles Bonnet syndrome[11].
The course, prognosis and treatment vary with the nature of the visual dysfunction. Some patients find the removal of underlying cause of visual impairment such as cataract extraction leading to improvement while other patients find the relief when the eye disease progresses to total blindness[2]. Treatment with antipsychotic and anticonvulsant was mostly unsatisfactory[6,12]. Various nonpharmacological interventions had been recommended such as reducing social isolation, engaging in personal hobbies and improvement of environmental condition especially withlighting at home are beneficial[13].
Hence, discussion of these phenomena with the patient is vital as assurance of their harmless nature will ease their anxiety and concern. At present, the best form of treatment appears to be reassurance, empathy and counseling about the condition. Moreover, the awareness of this syndrome among medical personnel[3,14] and ophthalmologists is vital as most visually impaired patients would often present to the ophthalmic clinic first.
In conclusion, with regard to such a group of patients especially elderly patients that possess the insight into the unreality of what they are seeing with a deteriorating vision, ophthalmologists should therefore raise the suspicion of possible Charles Bonnet syndrome. Accurate diagnosis is critical as incorrect diagnosis could lead to sufferers being referred to inpatient psychiatric care, which may be very distressing and is unlikely to reduce or eliminate the occurrence of hallucinations.
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