Saccades: A window to the brain in Parkinson’s Disease
Saccades are a high velocity eye movement that function to move the fovea to a new visual target. The complex processing of a saccade involves many cortical and subcortical brain regions. The brain regions involved in a saccade will differ depending on whether the shift in gaze is voluntary or driven by a visual stimulus. The complex neuroanatomy of saccades leads to saccadic dysfunction in a number of neurological disorders, such as Parkinson ’s disease (PD). PD patients experience hypometric saccades with increased latency, often requiring the use of multistep saccades to reach a visual target. They also have an increased proportion of involuntary express saccades. These pathological consequences can be studied by understanding the brain areas involved in the generation of a saccades as well as the areas that are affected in PD. In this way, saccadic eye movements can be viewed as a window into the brain, allowing their use to understand what structures are damaged simply by looking at an eye movement. Saccadometry, the study of saccades, can be used as a clinical tool in the PD population in the differential diagnosis and staging of PD, as well as evaluating the effects of treatments such as L-dopa or deep brain stimulation of the subthalamic nucleus on the disease. It can also allow us to understand where these treatments are working, by how they change saccades.