Complex Visual Hallucinations in the Visually Impaired

The phenomenon of a phantom limb is a common experience after a limb has been amputated or its sensory roots have been destroyed. A complete break of the spinal cord also often leads to a phantom body below the level of the break. Furthermore, a phantom of the breast, the penis, or of other innervated body parts is reported after surgical removal of the structure. A substantial number of children who are born without a limb feel a phantom of the missing part, suggesting that the neural network, or 'neuromatrix', that subserves body sensation has a genetically determined substrate that is modified by sensory experience.

Age-related macular degeneration (AMD), the leading cause of irreversible blindness and low vision among the elderly, has not been well studied with regard to its impact on daily life. This study was designed to demonstrate the impact of AMD on quality of life, emotional distress, and functional level. The study sample consisted of 86 elderly adults (average age, 79 years) with AMD who were legally blind in at least 1 eye. Participants completed a battery of measures that included the Quality of Well-being Scale, the Instrumental Activities of Daily Living index, self-rated general health status, and the Profile of Mood States. Persons with AMD experienced significant reductions in key aspects of daily life. Their ratings for quality of life (average Quality of Well-being Scale score=0.581) and emotional distress (average Profile of Mood States total score=65.36) were significantly worse than those for similarly aged community adults and were comparable with those reported by people with chronic illnesses (eg, arthritis, chronic obstructive pulmonary disease, acquired immunodeficiency syndrome, and bone marrow transplants). Patients with AMD were also more likely than a national sample of elderly individuals to need help with daily activities. Visual acuity was related to ability to carry out daily activities (Instrumental Activities of Daily Living, r=0.28, P=.008). Quality of life ratings were significantly related to the ability to carry out daily activities (r=-0.38, P=.001), self-rated general health status (r=-0.21, P=.05), and emotional distress (Profile of Mood States total score, r=-0.25, P=.02). Individuals with a shorter period of perceived vision loss were more likely to report high levels of emotional distress (r=-0.24, P=.03) than those with a longer period of perceived vision loss. Further, those who were blind in 1 eye were even more significantly distressed than those who were blind in both eyes. Elderly persons with AMD causing legal blindness in 1 or both eyes have significant emotional distress and profoundly reduced quality of life and need help with key daily activities.

Complex visual hallucinations may affect some normal individuals on going to sleep and are also seen in pathological states, often in association with a sleep disturbance. The content of these hallucinations is striking and relatively stereotyped, often involving animals and human figures in bright colours and dramatic settings. Conditions causing these hallucinations include narcolepsy-cataplexy syndrome, peduncular hallucinosis, treated idiopathic Parkinson's disease, Lewy body dementia without treatment, migraine coma, Charles Bonnet syndrome (visual hallucinations of the blind), schizophrenia, hallucinogen-induced states and epilepsy. We describe cases of hallucinosis due to several of these causes and expand on previous hypotheses to suggest three mechanisms underlying complex visual hallucinations. (i) Epileptic hallucinations are probably due to a direct irritative process acting on cortical centres integrating complex visual information. (ii) Visual pathway lesions cause defective visual input and may result in hallucinations from defective visual processing or an abnormal cortical release phenomenon. (iii) Brainstem lesions appear to affect ascending cholinergic and serotonergic pathways, and may also be implicated in Parkinson's disease. These brainstem abnormalities are often associated with disturbances of sleep. We discuss how these lesions, outside the primary visual system, may cause defective modulation of thalamocortical relationships leading to a release phenomenon. We suggest that perturbation of a distributed matrix may explain the production of similar, complex mental phenomena by relatively blunt insults at disparate sites.