SIR: We appreciate Dr. Terao's letter regarding our paper. Dr. Terao is of course correct that low visual acuity is associated with visual hallucinations in AD patients. We discussed this in the introduction to our paper, referring to our own work, and it has been confirmed by others, including Chapman et al. as noted by Dr. Terao. The visual acuities of the subjects were within ±10/20 in the "best eye" and thus were quite comparable between groups, and this should have been included in the paper. Dr. Terao notes the Charles Bonnet syndrome as one in which "psychologically normal old people can suffer from visual hallucinations." "Charles Bonnet syndrome" is just a descriptive term and not a diagnosis or an explanation. Research into the causes of this syndrome in fact show that eye disease and, quite possibly, early dementia are associated factors.2—4 Dr. Terao may be interested in the literature describing visual hallucinations in a variety of eye diseases.4—7
Dr. Terao notes that if our Alzheimer's patients actually included patients who had dementia with Lewy bodies, "DLB rather than occipital atrophy might have been associated with visual hallucinations." First, our patients met strict research criteria for AD.8,9 Definitive diagnosis can be made only at autopsy. Our patients did not demonstrate parkinsonism or fluctuation, making it unlikely they had DLB.9 Actually, given the high prevalence of visual hallucinations in DLB, we would hypothesize that decreased visual acuity and occipital atrophy may be associated factors of visual hallucinations in DLB.
We thank Dr. Terao for his interest in this relatively unexplored topic.