Extraordinary Claims Require Extraordinary Evidence: Centrally Mediated Preservation of Binocular Visual Field in Glaucoma is Unlikely

yesWe have read with interest the recent article by Sponsel et al.1 There is much evidence that glaucomatous damage occurs at the optic nerve head,2 and therefore we were surprised by the authors' conjecture that there may be a central mechanism that preserves the binocular visual field in advanced glaucoma

Visual Loss and Visual Hallucinations in Patients with Age-Related Macular Degeneration (Charles Bonnet Syndrome)

PURPOSE. The condition in which visual hallucinations (VHs) are solely associated with a visual impairment is termed Charles Bonnet Syndrome (CBS). The study was undertaken to investigate whether the extent of visual acuity (VA) loss and central visual field loss predisposes a patient with age-related macular degeneration (AMD) to develop a CBS VH and, in addition, whether the progression in loss is mirrored in the complexity of the VHs reported. VH phenomenology and CBS prevalence were also examined. METHODS. Sixty-six patients (age range, 63-96 years, mean Ϯ SD 81.2 Ϯ 7.1 years) with bilateral AMD were questioned as to whether they had experienced any hallucinatory episodes exclusive to vision. The four-point primary inclusion criterion ensured that all patients had bilateral AMD, a bilateral central scotoma, best monocular VA poorer than or equal to 0.6 logMAR (logarithm of the minimum angle of resolution) and intact cognition (using the Mini Mental State Examination for the Blind and the Telephone Interview for Cognitive Status). The patients who did not report VH were classified into the non-VH group, with the remainder in the VH group. An extended Institute of Psychiatry Structural Interview characterized the phenomenology of the VH. A secondary inclusion criterion subdivided the VH group into the apparent CBS group, in which personal medical history may have contributed to VH generation, and the manifest CBS group, where VHs were solely as a result of the visual loss. RESULTS. Fifty-three patients met the primary inclusion criterion: 32 were classified into the non-VH group and 21 into the VH group. The VH group were slightly younger (median difference, 4 years, P ϭ 0.03) and appeared to have a lower VA (median difference, 0.20 logMAR, P ϭ 0.08) and a more extensive visual field loss (P ϭ 0.06) than did the non-VH group. However, when these variables were evaluated simultaneously by logistic regression, only age emerged as a statistically significant predictor of VH (odds ratio 0.88, 95% confidence interval [CI] 0.8 -0.99, P ϭ 0.03). The prevalence of apparent CBS and manifest CBS in the AMD population was found to be 25% and 15%, respectively. With no clinical and phenomenological differences between the two CBS groups, the secondary inclusion criterion was withdrawn, the VH group was renamed the CBS group, and a prevalence of 40% was recalculated. Of the 82 visual phenomena experienced by the CBS group, 21 were classified as simple VHs and 39 as complex VHs, with the remainder classified as either entopic phenomena or visual inference. Patients who experienced both simple and complex VHs appeared to have a greater visual field loss (P ϭ 0.06) compared with those patients who reported either solely simple or solely complex VHs. CONCLUSIONS. The extent of visual loss did not appear to be a predictor for the likelihood of a patient with AMD experiencing a CBS VH, nor was the progression of loss reflected in the complexity of the VHs reported. 1,2 can occur in any sensory modality, and are most often generated through neurologic disease, psychopathology, and the use of drugs. 2-6 When visual hallucinations (VHs) follow marked visual acuity (VA) loss, in the absence of cognitive impairment, the condition is termed Charles Bonnet Syndrome (CBS), To ensure that there was little likelihood that factors such as cognitive impairment would contribute to the perception of the VH we applied a four-point primary inclusion criterion to the group of patients with AMD. A secondary two-point criterion subdivided the VH group into two groups: an apparent CBS group, in which concurrent medication and/or a diagnosed medical condition could have contributed to the generation of the VHs, and a manifest CBS group, in which there were no obvious causes for the VHs other than the marked visual impairment. Our findings suggest that the VH experienced by the apparent CBS group could not be differentiated from those described by the manifest CBS group. Furthermore, the extent of visual loss did not predict which patients would visually hallucinate, nor did it determine the complexity of the VHs reported. MATERIALS AND METHODS Study Inclusion Criteria An initial group of 66 consecutive fluent-English-speaking patients with AMD were recruited from the Manchester Roya