Visual symptoms are relatively common in
Parkinson's disease (PD) and optical coherence tomography has indicated possible
retinal thinning. Accumulation of aggregated α-
synuclein is thought to be a central pathogenic event in the PD brain but there have not as yet been reports of
retinal synucleinopathy.
Retinal wholemounts were prepared from subjects with a primary clinicopathological diagnosis of PD (N=9),
dementia with Lewy bodies (DLB; N=3),
Alzheimer's disease (N=
3), progressive supranuclear palsy (N=2) as well as elderly normal control subjects (N=4). These were immunohistochemically stained with an antibody against α-
synuclein phosphorylated at
serine 129, which is a specific molecular marker of
synucleinopathy. Phosphorylated α-
synuclein-immunoreactive (p-syn IR) nerve fibers were present in 7/9 PD subjects and in 1/3 DLB subjects; these were sparsely distributed and superficially located near or at the inner
retinal surface. The fibers were either long and straight or branching, often with multiple en-passant varicosities along their length. The straight fibers most often had an orientation that was radial with respect to the optic disk. Together, these features are suggestive of either retinopetal/centrifugal fibers or of
ganglion cell axons. In one PD subject there were sparse p-syn IR neuronal cell bodies with dendritic morphology suggestive of G19 retinal ganglion cells or intrinsically photosensitive
ganglion cells. There were no stained nerve fibers or other specific staining in any of the non-PD or non-DLB subjects. It is possible that at least some of the observed visual function impairments in PD subjects might be due to α-
synucleinopathy.