Dopaminergic Retinal Cell Loss and Visual Dysfunction in Parkinson Disease

Area of Science:

• Neuroscience
• Ophthalmology
• Pathology

Background:

• The retina's role in Parkinson disease (PD) pathology is increasingly recognized.
• Dopaminergic cells in the retina are crucial for visual processing.

Purpose of the Study:

• To investigate the state of dopaminergic amacrine cells and their postsynaptic neurons in the retina of PD patients.
• To analyze the impact of PD on retinal cell morphology, number, and synaptic connections.

Main Methods:

• Immunohistochemistry and confocal microscopy were used on human donor eyes (control and PD).
• Evaluated morphology, cell counts, and synaptic contacts of dopaminergic amacrine cells, AII amacrine cells, and melanopsin-containing retinal ganglion cells.

Main Results:

• PD eyes showed reduced dopaminergic amacrine cell numbers (26-58%) across retinal regions.
• Synaptic contacts with AII amacrine cells decreased by 60% and with melanopsin cells by 35%.
• AII amacrine cells exhibited mitochondrial loss and decreased connexin 36, indicating functional impairment despite unchanged numbers.

Conclusions:

• Retinal dopaminergic system impairment and AII cell alterations may explain reduced contrast sensitivity in PD.
• Dopamine reduction and synaptic loss contribute to melanopsin cell loss and circadian rhythm disturbances in PD.
• The retina mirrors brain neurodegeneration, indicating significant involvement in PD pathology.