Complex Visual Hallucinations and

Macular Degeneration

by Erik A. Steen

Located in the center of the retina, the sensitive macula provides us with sight in the center of our field of vision. When we look directly at something, the macula allows us to see the fine details. This sharp, straight-ahead vision is necessary for driving, reading, recognizing faces, and doing close work, such as sewing. Macular degeneration is the impairment of this central macular area. Age-related macular degeneration (AMD) is the most common cause of vision loss in the Western world in the over 50 age group. It most commonly affects those of northern European descent and is uncommon in African-Americans and Hispanics. The prevalence increases with age. It affects about 15% of the population by age 55, and over 30% are affected by age 75 (Miller, 1992).

In macular degeneration a layer beneath the retina, called the retinal pigment epithelium (RPE), gradually wears out from its lifelong duties of disposing of retinal waste products. Eventually the capacity of the RPE layer to handle these metabolic products is overwhelmed and the RPE begins to degenerate (Miller, 1992). Other deep layers involved in development of macular degeneration are Bruch's membrane and the choroid layer. Additional factors that may hasten loss of the RPE layer, and the resulting degeneration of the central retina (macula) include hereditary factors, ultraviolet rays from sunlight, and blue iris color (more UV rays reach the retina in blue-eyed patients, probably because of the lower pigment density in the eye).

There are basically two forms of macular degeneration. So-called dry (or atrophic) macular degeneration, which accounts for 90% of cases, is caused by the aging and thinning of the tissues of the macula (Miller, 1992). This type is characterized by tiny yellowish deposits under the macular part of the retina. These deposits are known as drusen and may increase in size and number over time. Areas of loss of retinal and RPE layers in the macula may gradually appear. Small clumps of brown pigment from the degenerating RPE layer also are commonly seen.

The other major form of this disease is wet (or exudative macular degeneration) which is a much greater threat to vision loss even though it accounts for only 10% of cases. This type can be associated with a more sudden loss of vision due to leakage or bleeding under the macula from abnormal vessels, called the choriocapillaris, arising from one of the deeper layers. Eventually these areas of bleeding or fluid accumulation can develop into a dense mass of scar tissue beneath the retina, resulting in permanent loss of central vision (Foerster, 1976).

For a small percentage of people diagnosed with macular degeneration the loss of central vision is the least of their problems.The occurrence of complex visual hallucinations in people with age-related macular degeneration is not uncommon. These visual hallucinations in the elderly are sometimes known as the Charles Bonnet syndrome (CBS), named after the Swiss philosopher who described the phenomenon in his grandfather, Charles Lullin, in 1769 (Berrios & Brook, 1982). Lullin underwent bilateral cataract extraction followed, at age 89, by an episode of vividly formed visual hallucinations in the absence of any cognitive impairment. Lullin retained insight into the unreality of the experiences. Morsier first applied Bonnet's name to the syndrome but discounted the role of ocular disease, instead postulating pathology involving the processing of visual stimuli in the central nervous system. More recently, the term has been applied to any elderly patient with visual hallucinations. Various explanations have been proposed for visual hallucinations in partial blindness. Psychological explanations focus on regression and emergence of the primary process in conditions of reduced sensory input (Rosenbaum & Freedman, 1987). Physiological explanations have also been proposed. Lack of the usual afferent impulses due to ocular pathology, post surgical eye patching, or deprivation of visual sensory stimulation may unmask spontaneous neuronal activity at any of the various levels of processing of visual stimuli (Rosenbaum & Freedman, 1987). These are sometimes referred to as release hallucinations.

Charles Bonnet hallucinations occur in elderly people with severe visual sensory deprivation. This disease is frequently overlooked or misdiagnosed by both ophthalmologists and psychiatrist. CBS patients experience these complex visual hallucinations during clear consciousness. That is, psychosis, substance abuse, sleep disorders, focal neurological lesions and acute eye disease are absent. CBS subjects have reduced vision due to peripheral or central eye disease, i.e. macular degeneration. Individual hallucinations can last from a few seconds to most of the day. Episodes can occur for periods ranging from days to years, with hallucinations changing in both frequency and complexity during this time. The hallucinations may be triggered or stopped by many factors that operate via a general arousal mechanism (Casey & Wandzilak, 1988).

CBS patients most often report people, animals, buildings and scenery. These images may appear static, dynamic or animated. Subjects may react positively or negatively to their visual hallucinations. Additional common characteristics include no personal meaning for the content of the hallucinations and hallucinations vanishing when patients close their eyes. Also, most CBS subjects suffer from social isolation. Several theories may explain CBS. The most popular theory builds on sensory deprivation and emphasizes visual system activity following sensory loss producing nerve impulses and visual experiences (Lalla & Primeau, 1993). Reduced visual input cannot be the only cause of CBS because not all visually disabled people have visual hallucinations, and CBS has been described in patients with normal vision.

Previous studies link cognitive deficits with visual hallucinations. Cognitive deficits in Parkinson's disorder patients have also been associated with risk of hallucinations. A study of patients with Charles Bonnet Syndrome revealed that two of six subsequently developed dementia, which raises the question of whether visual hallucinations in patients with age-related macular degeneration may be a risk factor for or, more likely, an early symptom of dementia (Lalla & Primeau, 1993). A follow-up study of these patients may answer this question. The nearly significant association between older age and hallucinations could also indicate that greater age related cortical atrophy is a risk factor, but no there is no data to support or refute this possibility (James, 1993). The work of Foerster (1976), who produced complex visual hallucinations by stimulating the visual association cortex, makes visual association cortex area 19 a possible candidate for the brain region "releasing" visual hallucinations. Interestingly, an abnormally high number of neurofibrillary tangles are found in the visual association cortex of patients with Alzheimer's disease, a disease in which 10% of patients have visual hallucinations, with relative sparing of the primary visual cortex (Holroyd, et al. 1992). An examination of phenomena in other visual disorders and over a broader age range is now underway. These new studies may help clarify the importance of age as a risk factor. It will also help clarify whether this phenomenon is present in visual disorders with different pathologies and will further define other factors found in association with macular degeneration with hallucinations. Future studies of visual disorders in young patients, and of brain structure and function with magnetic resonance imaging, single-photon emission computed tomography, and autopsy to examine the role of abnormal neuroanatomy and neurophysiology would be of value to study this phenomenon also.

References

Berrios, G.E. & Brook, P. (1982). The Charles Bonnet syndrome and the problem of visual perceptual disorders in the elderly. Age and Aging, 11, 17-23.

Casey, D.A. & Wandzilak, T. (1988). Senile macular degeneration and psychosis. Journal of Geriatric Psychiatry and Neurology, 1, 108-110.

Foerster, R.E. (1976). Hallucinations within the brain. Journal of Neuropsychiarty, 35, 677-706.

Halroyd, S. Rabins, P.V. & Finklestein, D. (1992). Visual hallucinations in patients with macular degeneration. American Journal of Psychiatry, 149:22, 1701-1706.

James, A.G. (1993). Hearing and premorbid personality in paranoid states. Journal of Geriatric Psychiatry and Neurology, 12, 66-72.

Lalla, D. & Primeau, F. (1993). Complex visual hallucinations in macular degeneration. Canadian Journal of Psychiatry, 38, 584-587.

Miller, R.H. (1992). Macular degeneration: physiological causes. Neurology, 40, 444-449.

Rosenbaum, F. & Freedman, M. (1987). Visual hallucinations in sane people: Charles Bonnet syndrome. Journal of Geriatric Psychiatry and Neurology, 35, 66-68.