Retinal nerve fiber layer thickness and visual hallucinations in Parkinson's Disease

Abstract

Defective visual information processing from both central and peripheral pathways is one of the suggested mechanisms of visual hallucination in Parkinson's disease (PD). To investigate the role of retinal thinning for visual hallucination in PD, we conducted a case-control study using spectral domain optical coherence tomography. We examined a representative sample of 61 patients with PD and 30 healthy controls who had no history of ophthalmic diseases. General ophthalmologic examinations and optical coherence tomography scans were performed in each participant. Total macular thickness and the thickness of each retinal layer on horizontal scans through the fovea were compared between the groups. In a comparison between patients with PD and healthy controls, there was significant parafoveal inner nuclear layer thinning, whereas other retinal layers, including the retinal nerve fiber layer, as well as total macular thicknesses were not different. In terms of visual hallucinations among the PD subgroups, only retinal nerve fiber layer thickness differed significantly, whereas total macular thickness and the thickness of other retinal layers did not differ. The retinal nerve fiber layer was thinnest in the group that had hallucinations without dementia, followed by the group that had hallucinations with dementia, and the group that had no hallucinations and no dementia. General ophthalmologic examinations did not reveal any significant correlation with hallucinations. There were no significant correlations between retinal thicknesses and duration or severity of PD and medication dosages. The results indicate that retinal nerve fiber layer thinning may be related to visual hallucination in nondemented patients with PD. Replication studies as well as further studies to elucidate the mechanism of thinning are warranted.

Imagine that: elevated sensory strength of mental imagery in individuals with Parkinson's disease and visual hallucinations

“…However, hallucinations in PD are often of complex objects (such as faces or people), suggesting that these perceptual abnormalities only occur once neural activity in the primary visual system interacts with the ventral visual stream in the temporal lobe, a known site of Lewy body pathology in PD patients with hallucinations [15,26]. In addition, a number of recent studies have highlighted pathological impairments in the visual system of individuals with hallucinations, both in the retina [27] and dorsal visual stream [21,22], suggesting that hallucinations are due to a combination of impaired visual input with concomitant exogenous attentional dysfunction [3,28]. This accords with recent investigations into pareidolia-visual misperceptions closely related to hallucinations [29]-which are similarly mediated by topdown attentional control mechanisms [30,31].…”

Characterization of retinal architecture in Parkinson's disease

“…Within the past few years, there has been a significant focus on intraretinal segmentation in OCT studies in PD [17,[23][24][25]. The primary findings of these studies are summarized in Table 2.…”

Retinal Microvascular Impairment in the Early Stages of Parkinson's Disease

“…4,[15][16][17] Comparatively, the study of vessel changes in the retina in PD has received less attention due to the lack of suitable modality to image the microvascular network in vivo. In recent years, OCT angiography (OCT-A) was extended based on OCT technology, which can be used to characterize the three-dimensional (3D) vasculature in various retinal layers, providing quantitative assessment of the microvascular and morphological structure in the retina.…”