Assessment of Three-dimensional Vision Alteration in Parkinson Disease

Overview

Parkinson's disease is characterized by motor deficits, improved by dopaminergic intakes. Besides motor symptoms, visual troubles are observed in patients with Parkinson's disease, in particular spatial orientation problems including 3D vision. However, although these visual disturbances are commonly reported by the patients and their family in our clinical experience, they have not been the subject of specific clinical studies yet. Parkinsonian patients report deficits in 3D vision leading to a loss of visuomotor ability, locomotor functions and to falls. Despite these frequent complaints, little is known about 3D vision in Parkinson's disease. The investigators want in this project to precisely estimate 3D deficits in parkinsonian patients by assessing their psychophysical performances in 3D vision tasks to compare to age matched control subjects' performances.

This is a monocentric and prospective study that will compare Parkinsonian patients versus healthy subjects on the execution of psychophysical tests and Visual Evoked Potentials without and with L Dopa. The comparison will focus on one hand between PD patients and control subjects (matched by age and sex to parkinsonian patients) and on the other hand between parkinsonian patients in ON and OFF drug conditions. Psychophysical measurements of 3D perception will be performed during this study. This will be done by asking the subjects to indicate with a joystick whether they perceived the stimulus presented on the screen placed in front of them like being 2D or 3D. Two "depth conditions" will be tested; 2D for flat stimuli and 3D for in depth stimuli. Two "3D-cues" conditions will be tested: binocular cues (retinal disparity) and monocular cues (perspective). Their performances will be assessed in both L Dopa ON and OFF conditions randomly determined. While subjects will be performing the psychophysical tasks, we will record the visual potentials evoked by the presentation of the 2D/3D visual stimuli. Visual Evoked Potentials are obtained by extracting from the EEG the electrical signals temporally locked to the visual stimulations. 3D perception is at the intersection of pure visual perception and navigation; indeed, any movement in a familiar or unfamiliar environment requires an adequate balance between the reality of the three-dimensional environing space and its mental representation. So one of the major roles of the visual system is to convert the two-dimensional retinal images into 3 dimensions. With both binocular (retinal disparity, eye vergence) and monocular (perspective, shading ...) cues, the 3D vision can estimate (1) the distance between objects (2) distance between an object and itself, (3) relief or depth of an object. Altering that perception affects the postural and locomotor functions and thus must worsen motor disorders. So far, no systematic studies have been conducted in parkinsonian patients to quantify their 3D perception. Because of the interaction between 3D perception and motor outcomes, we want, in this project, to estimate the 3D visual deficits, to understand the underlying altered processes, to test the effect of L Dopa on these deficits and to specify the relationship between 3D visual and motor deficits. 3D psychophysical performances using a categorization task and their underlying neuronal mechanisms measured with VEP will be assessed in both Parkinsonian patients and control subjects in a randomized and comparative study. Parkinsonian patients will be hospitalized for less than 48 hours. Patients randomized in order OFF-ON L Dopa condition will arrive at 8 am. They will perform the first part of the experiment in OFF condition. Later they will receive 150% of their usual treatment dose, perform the experiment and leave the hospital. Patients randomized in order ON-OFF will arrive at 8 am to receive 150% of their usual treatment dose and perform the experiment. The following day, they will perform the experiment weaned from any dopaminergic therapy since midnight in OFF condition. They will leave the hospital after receiving their usual treatment dose.