Assessment of Three-dimensional Vision Alteration in Parkinson Disease
Condition: Parkinson Disease
MeSH terms: Parkinson Disease
Study type: Interventional

Summary: 
      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.
    

Detailed description: 
      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.
    

Intervention name(s): Psychophysical measurements of 3D perception
Intervention type(s): Other
Intervention description(s): 3D psychophysical performances using a categorization tasks and their underlying mechanisms measured with visual evoked potentials will be assessed in a randomized and comparative study. The order of psychophysical and visual evoked potentials experiments will be randomized between the L Dopa ON and OFF conditions. The randomization will be done by the clinical investigational center. The comparisons will be made between parkinsonian patient and control subjects, and between parkinsonian patients in L Dopa ON and OFF conditions.
Allocation: Randomized
Intervention model: Parallel Assignment
Masking: None (Open Label)
Primary purpose: Basic Science
Keywords: three-dimensional vision; Parkinson