Changes in Pattern Electroretinograms to Equiluminant Red-Green and Blue-Yellow Gratings in Patients with Early Parkinson’s Disease

Abstract

In Parkinson's disease (PD), the luminance pattern electroretinogram (PERG) is reported to be abnormal, indicating dysfunction of retinal ganglion cells (RGCs). To determine the vulnerability of different subpopulations of RGCs in PD patients, the authors recorded the PERG to stimuli of chromatic (red-green [R-G] and blue-yellow [B-Y]) and achromatic (yellow-black [Y-Bk]) contrast, known to emphasize the contribution of parvocellular, koniocellular, and magnocellular RGCs, respectively. Subjects were early PD patients (n = 12; mean age, 60.1 +/- 8.3 years; range, 46 to 74 years) not undergoing treatment with levodopa and age-sex-matched controls (n = 12). Pattern electroretinograms were recorded monocularly in response to equiluminant R-G, B-Y, and Y-Bk horizontal gratings of 0.3 c/deg and 90% contrast, reversed at 1Hz, and presented at a viewing distance of 24 cm (59.2 x 59 degree field). In PD patients, the PERG amplitude was significantly reduced (by 40 to 50% on average) for both chromatic and luminance stimuli. Pattern electroretinogram latency was significantly delayed (by about 15 ms) for B-Y stimuli only. Data indicate that, in addition to achromatic PERGs, chromatic PERGs are altered in PD before levodopa therapy. Overall, chromatic PERGs to B-Y equiluminant stimuli exhibited the largest changes. Data are consistent with previous findings in PD, showing that visual evoked potentials (VEP) to B-Y chromatic stimuli are more delayed than VEPs to R-G and achromatic stimuli. The results suggest that the koniocellular subpopulation of RGCs may be particularly vulnerable in early stages of Parkinson's disease.

Chromatic pattern-reversal electroretinograms (ChPERGs) are spared in multiple system atrophy compared with Parkinson’s disease

“…PERG abnormalities in IPD have been related to dopaminergic deficiency [33][34][35][36], as they are found in cases of neuroleptic-induced Parkinsonism and can be corrected by l-dopa administration [1,37]. A retinal dopaminergic component for visual dysfunction in IPD has been proposed by several authors [3,8,34,38]. Indeed, the retina contains both dopaminergic neurons [33] and dopaminergic receptors (D1 and D2) [3,5,39].…”

“…Only luminance PERGs have been tested in IPD and MSA and they were less impaired in the latter [43]. As far as concerns ChPERG, the visual deficits of the blue cone pathway in IPD are likely to be dopamine [8]. In the retina, dopamine is localised in the amacrine and interplexiform cells, playing a role in modulating the centre-surround organisation of the receptive field of retinal ganglion cells [44,45].…”

“…The equiluminance was established psychophysically for every subject with a variant of the method of heterochromatic flicker photometry [24]. More details can be found elsewhere [8,22].…”

“…1). PERGs showed a typical positive-negative waveform (P1-N1) [8]; latencies and amplitudes of different waves were measured using the cursor with the digital readout on the monitor: amplitudes from peak to peak, latencies at P1 peak. Sweep duration was 350 ms.…”

“…Impairment of achromatic as well as chromatic vision in idiopathic Parkinson's disease (IPD) has been extensively proven in recent years using clinical, psychophysiological and electrophysiological methods (electroretinograms, ERGs, and visual evoked potentials, VEPs) and attributed to dopaminergic deficiency at the retina level [1][2][3][4][5][6][7][8].…”