Bioelectrical function and structural assessment of the retina in patients with early stages of Parkinson's disease (PD).

Barbara Nowacka,Andrzej Potemkowski,Krystyna Honczarenko,Wojciech Lubiński,Krzysztof Safranow

doi:10.1007/s10633-015-9503-0

Abstract

Purpose To determine bioelectrical function and structural changes of the retina in patients with early stages of Parkinson’s disease (PD).Materials and methodsThirty-eight eyes of 20 patients with early idiopathic PD and 38 eyes of 20 healthy age- and sex-matched controls were ophthalmologically examined, including assessment of distance best-corrected visual acuity (DBCVA), slit lamp examination of the anterior and posterior segment of the eye, evaluation of the eye structures: paramacular retinal thickness (RT) and retinal nerve fiber layer (RNFL) thickness with the aid of OCT, and the bioelectrical function by full-field electroretinogram (ERG). Additionally, PD patients were interviewed as to the presence of dopamine-dependent visual functions abnormalities.ResultsIn patients with early PD, statistically significant changes in comparison with the control group were observed in ERG. They contained a reduction in mean amplitudes of the scotopic a-wave (rod–cone response), the scotopic oscillatory potentials (OPs)—OP2 and OP3, the photopic b-wave, and a reduction in the overall index (OP1 + OP2 + OP3) and a prolongation of mean peak times of the scotopic OP1, OP2, OP3, OP4 (p < 0.05). A questionnaire concerning abnormalities of dopamine-dependent visual functions revealed that PD patients with abnormal peak times of OP1, OP2, and OP3 reported non-specific visual disturbances more frequently in comparison with PD patients with normal peak times of OPs. Other analyzed parameters of ERG, DBCVA, RT, and RNFL did not significantly differ between patients with PD and the control group.ConclusionIn patients with early PD, bioelectrical dysfunction of the retina was observed in the ERG test, probably as a result of dopamine deficiency in the retina. The results of our study indicate that ERG may also be a useful tool for understanding the reason for non-specific visual disturbances occurring in PD patients.

Highlights

Parkinson’s disease (PD) is the neurodegenerative disorder characterized by a deficiency of the neurotransmitter—dopamine in the central and peripheral nervous system, including visual pathways
A questionnaire concerning abnormalities of dopamine-dependent visual functions revealed that PD patients with abnormal peak times of OP1, OP2, and OP3 reported non-specific visual disturbances more frequently in comparison with PD patients with normal peak times of oscillatory potentials (OPs)
In patients with early PD, bioelectrical dysfunction of the retina was observed in the ERG test, probably as a result of dopamine deficiency in the retina

Summary

Introduction

Parkinson’s disease (PD) is the neurodegenerative disorder characterized by a deficiency of the neurotransmitter—dopamine in the central and peripheral nervous system, including visual pathways. Dopamine is contained in an A18 subtype of amacrine cells of the retinal inner plexiform layer [1] Despite of their low density, their widespread dendritic organization and long fine axons ensure overlap with neighboring amacrine cells and bipolar cells and direct influence through synapses [2]. The functional changes may appear even with the normal morphology of the retina and the optic nerve, probably as a result of diminished dopaminergic activity in the visual system. These changes can be detected with the aid of electrophysiological examinations. Electrophysiological evidence of visual pathology in early PD has been related to delayed light peak in the electrooculogram (EOG) [7], amplitude reductions in the pattern electroretinogram (PERG) [17], and delays in visually evoked potentials (PVEP) [17]

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