Retinal Abnormalities as Biomarker of Disease Progression and Early Diagnosis of Parkinson Disease

The retina is actually brain tissue and is considered part of the central nervous system (CNS). It is the only part of the CNS that can be visualized directly and non-invasively. There is already a body of evidence that retinal neurons accumulate alpha-synuclein and degenerate in Parkinson disease (PD). Whether retinal imaging could be useful as an objective biomarker to track disease progression and response to disease-modifying treatments in patients with PD is not known. While there are a variety of imaging techniques available (e.g., PET, SPECT, MRI), none of them has emerged as a fully reliable method to accurately measure clinical progression in PD. The structure of the retina can be studied easily in vivo using spectral domain high definition optical coherence tomography (OCT), a non-invasive imaging technique with a resolution of \~1 microns (0.001 mm). OCT quantifies the thickness of the different retinal layers. The primary aim of this proposal is to determine whether OCT is a reliable clinical measure that can objectively measure clinical progression in PD. Our group has shown recently that OCT can be used as a means to measure progressive neuronal loss in the retina in patients with a synucleinopathy closely related to PD (multiple system atrophy, MSA). In MSA, retinal degeneration was closely associated with disease severity and progressively worsened overtime in a predictable fashion, sufficient for biostatistical modeling. We now want to find out if this is also true in PD. There is a panel of non-motor clinical features that increase the risk of developing PD. We propose to measure retinal nerve fiber density in these patients considering them as "pre-motor" PD and follow their clinical evolution overtime. If OCT proves useful as a means to identify pre-motor PD, such a result would present an important therapeutic window to intervene with disease modifying drugs and to prevent the development of CNS deficits. We plan to determine whether retinal morphology can be correlated with visual function using complementary measures of visual electrophysiology techniques, including pattern electroretinogram (PERG) and photopic negative response (PhNR). These techniques have been used in patients with PD and other synucleinopathies, and do map closely to retinal function abnormalities. But, there is little data describing how these functional measure of the retina progression over time in PD. We hypothesize that patients with PD have specific patterns of damage in retinal structure and function, that this pattern can be identified in the premotor phase, We believe that OCT can be used as an objective biomarker of premotor diagnosis and disease progression. INNOVATION: The structure of the retina presents an ideal opportunity to image the CNS overtime with OCT. As a widely available clinical technique that correlates closely with functional measures of visual electrophysiology, OCT is being increasingly used in multiple sclerosis and other neurodegenerative disorders. If successful, this work may provide a significant tool for the diagnosis of PD in the pre-motor phase and could be used as a clinical outcome measure in disease-modifying trials. To achieve these objectives, we will take advantage of the infrastructure used in the ongoing NIH-funded Natural History of Autonomic Disorders study (ClnicalTrials.gov: NCT01799915), which prospectively follows patients with synucleinopathies with standardized neurological measures overtime. The proposal will provide measures of retinal structure in conjunction with measures of disease severity in a group of patients with well-defined PD. By measuring retinal structure in a group of patients considered high risk for developing PD (namely REM sleep behavior disorder -RBD, and isolated autonomic failure) we will determine the usefulness of OCT as a mean to identify PD in the premotor phase.